Paper - Comparative studies on the growth of the cerebral cortex 4 (1918)

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Sugita N. Comparative studies on the growth of the cerebral cortex. IV. On the thickness of the cerebral cortex of the Norway rat (Mus norvegicus) and a comparison of the same with the cortical thickness in the albino rat. (1918) J Comp. Neurol. 29: 11-.

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This 1917 fourth in a series of historic papers by Sugita on the development of the cortex in the rat. More by this author: Sugita N. Comparative studies on the growth of the cerebral cortex. I. On the changes in the size and shape of the cerebrum during the postnatal growth of the brain. Albino rat. (1917) J Comp. Neurol. 28: 495-. Sugita N. Comparative studies on the growth of the cerebral cortex. II. On the increases in the thickness of the cerebral cortex during the postnatal growth of the brain. Albino rat. (1917) J Comp. Neurol. 28: 511-. Sugita N. Comparative studies on the growth of the cerebral cortex. III. On the size and shape of the cerebrum in the Norway rat (Mus norvegicus) and a comparison of these with the corresponding characters in the albino rat. (1918) J Comp. Neurol. 29: 1-. Sugita N. Comparative studies on the growth of the cerebral cortex. IV. On the thickness of the cerebral cortex of the Norway rat (Mus norvegicus) and a comparison of the same with the cortical thickness in the albino rat. (1918) J Comp. Neurol. 29: 11-. Sugita N. Comparative studies on the growth of the cerebral cortex. V. Part I. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal sections of the albino rat brain, together with the changes in these characters according to the growth of the brain. V. Part II. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal sections of the brain of the Norway rat (Mus norvegicus), compared with the c responding data for the albino rat. (1918) J Comp. Neurol. 29: 61-117. Sugita N. Comparative studies on the growth of the cerebral cortex. VI. Part I. On the increase in size and on the developmental changes of some nerve cells in the cerebral cortex of the albino rat during the growth of the brain. VI. Part II. On the increase in size of some nerve cells in the cerebral cortex of the Norway rat (Mus norvegicus), compared with the corresponding changes in the albino rat. (1918) J Comp. Neurol. 29: 119-. Sugita N. Comparative studies on the growth of the cerebral cortex. VII. On the influence of starvation at an early age upon the development of the cerebral cortex. Albino rat. (1918) J Comp. Neurol. 29: 177-. Sugita N. Comparative studies on the growth of the cerebral cortex. VIII. General review of data for the thickness of the cerebral cortex and the size of the cortical cells in several mammals, together with some postnatal growth changes in these structures. (1918) J Comp. Neurol. 29: 241-. Modern Notes: cortex | rat Neural Links: ectoderm | neural | neural crest | ventricular | sensory | Stage 22 | gliogenesis | neural fetal | Medicine Lecture - Neural | Lecture - Ectoderm | Lecture - Neural Crest | Lab - Early Neural | neural abnormalities | folic acid | iodine deficiency | Fetal Alcohol Syndrome | neural postnatal | neural examination | Histology | Historic Neural | Category:Neural

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Comparative Studies on the Growth of the Cerebral Cortex

IV. On the Thickness of the Cerebral Cortex of the Norway Rat (Mus Norvegicus) and a Comparison of the Same with the Cortical Thickness in the Albino Rat

Prof. Naoki Sugita (1887-1949)

Naoki Sugita

From the Wistar Institute of Anatomy and Biology

Ten Charts

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Contents 1 Comparative Studies on the Growth of the Cerebral Cortex 1.1 IV. On the Thickness of the Cerebral Cortex of the Norway Rat (Mus Norvegicus) and a Comparison of the Same with the Cortical Thickness in the Albino Rat 1.2 I. Introduction 1.2.1 Table 1 1.2.2 Table 2 Comparative Studies on the Growth of the Cerebral Cortex[edit] IV. On the Thickness of the Cerebral Cortex of the Norway Rat (Mus Norvegicus) and a Comparison of the Same with the Cortical Thickness in the Albino Rat[edit] Prof. Naoki Sugita (1887-1949) Prof. Naoki Sugita (1887-1949) Naoki Sugita

From the Wistar Institute of Anatomy and Biology

Ten Charts

I. Introduction[edit] In my second study in this series (Sugita, '17a), I described in detail the postnatal growth of the cortex in thickness in the brain of the albino rat. With the same purpose and by the same technique, I have examined also the growth of the cerebral cortex of the Norway rat, the wild form from which the albino rat has been derived. Donaldson and Hatai ('11) have been interested in a comparison of the wild Norway with the albino rats in respect of their body measurements and the size of the central nervous system. They have concluded that on account of domestication the albino rat grows less well than the wild Norway rat, from which it has been derived, and especially that the relative weight of the brain of the adult albino rat is about 16 per cent less than that of the Norway rat of like body weight. It has been assumed as probable that the greater weight of the brain in the Norway rat is due to an enlargement of the constituent neurons rather than to an increase in their number. The percentage of water appears to be nearly the same in the central nervous system of both forms during the period of active growth, but after this period it remains slightly higher in the Norway rat. From these differences between the two forms as regards the weight and the water content of their brains, it is also inferred that there will be some structural

1]

12 NAOKI SUGITA

differences in the cerebral cortex. Consequently, it became desirable for me to compare in these two forms, one wild and aggressive and -the other gentle and domesticated, the course of the growth of the cerebral cortex.

Using my previous studies on the Albino (Sugita, '17a) and on the form of the Norway brain (Sugita, '18) as a point of de-. parture, I will present in this paper the data on the cortical thickness of the Norway rat and will compare these with the data for the Albino. In this comparison of the brains of the two forms, the data, other than those on cortical thickness, are all quoted from Donaldson and Hatai ('11, '15).

II. MATERIAL

The Noxway rats used in this study, were all supplied through the courtesy of The Wistar Institute and were trapped alive in Philadelphia and its vicinity, between April and November, 1916. There were 36 males and 18 females, representing every stage of growth between 17 and 394 grams in body weight. In the preparation of the material and the arrangement of the data, the same methods as those described in my former study on the Albino (Sugita, '17a) were followed. For the discrimination of a Ncfway group from an albino group of the same tabular number, the Norway records carry the capital letter N before their group number.

The following tables, tables 1 and 2, give the sex, body and tail lengths, and body and brain weights of the Norway rats used in this study, grouped according to their brain weights and averaged for each group. Table 1 contains the material used for the sagittal and frontal sections and table 2 that for the horizontal sections.

Comparing the body measurements of this series with those given in table 85 in The Rat" (Donaldson, '15), it is found that the average values for my material by groups correspond fairly well with the table values.

The increase in the body measurements of the Norway rat according to age is imperfectly known, so that we can not infer the age from the body measurements with any exactness.

Table 1[edit] TABLE 1

Showing the sex, body weight and length, tail length and brain weight of the Norway rats used in this study (sagittal and frontal sections) accompanied by the averages for each brain weight group

NO.

LITTER NO.

SEX

BODY WEIGHT

BODY LENGTH

TAIL LENGTH

BRAIN WEIGHT

grams

mm.

7)1 m.

grams

NXI b

(1)

m

19.8

84

41

1.155

a

(1)

m

20.8

86

44

1.160

i

(2)

m

17.8

85

65

1.175

19.5

85

50

1.164

NXII

N XIII a

(3)

m

35.3

110

66

1.369

35.3

110

86

1.369

NXIVb

(4)

m

33.1

104

84

1.407

g

(3)

m

37.5

112

88

1.429

a

(4)

m

33.8

113

94

1.431

i

(3)

m

36.3

107

86

1.431

e

(5)

m

43.6

124

108

1.437

k

(3)

f

36.1

112

87

1.445

36.7

112

91

1.430

NXVc

m

42.6

122

102

1.517

e

m

66.7

135

114

1.557

54.7

129

108

1.537

NXVI a

m

74.8

137

1.619

g

m

54.8

130

107

1.632

e

m

56.3

128

105

1.636

62.0

132

106

1 .'629

N XVII e

f

81.0

152

120

1.710

g

m

57.0

137

113

1.721

a

f

118.5

172

136

1.738

c

f

104.0

164

132

1.788

90.1

156

125

1.739

N XVIII c

f

136.9

157

147

1.825

a

m

128.1

177

142

1.833

132.5

167

145

1.829

NXIX b

m

160.7

177

158

1.962

a

f

251.0

210

174

1.981

205.9

194

166

1.972

14

TABLE I — Coitinnol

NO.

LITTER NO.

SEX

BODY WEIGHT

BODY LENGTH

TAIL LENGTH

BRAIN WEIGHT

grams

mm.

mm.

grams

NXX c

f

254.0

215

180

2.015

a

(1)

f

253.1

213

2.089

253.6

2H

180

2.052

NXXI g

m

331.0

215

195

2.156

d m

231.8

215

174

2.187

281.4

215

185

2.172

NXXII

N XXIII a

m

394.0

256

202

2.345

3H.0

256

202

2.345

Table 2[edit] TABLE 2

Showing the sex, body tveight and length, tail length and brain weight of the Norway rats used in this study (horizontal sections) accompanied by the averages for each brain weight group

NO.

LITTER NO.

SEX

BODY WEIGHT

BODY LENGTH

T.\IL LENGTH

BRAIN WEIGHT

grams

mm.

mm.

grams

NXI d

(1)

m

20.0

85

42

1.133

h

(2)

m

17.0

83

64

1.160

c

(1)

m

20.7

87

41

1.199

19.2

85

49

1.164

NXII

N XIII b

(3)

m

35.7

lOS

87

1.343

35.7

108

87

1.343

N XIV c

(4)

m

31.7

103

83

1.407

h

(3)

m

38.7

111

87

1.428

J

(3)

m

38.4

115

88

1.443

f

(5)

f

43.8

126

102

1.475

d

(4)

m

34.7

108

87

1.481

37.1

113

89

1.447

NXV b

m

48.5

121

100

1.511

d

m

54.1

122

101

1.529

51.3

122

101

/ 520

TABLE 2— Contmued

NO.

LITTER NO.

SEX

BODY WEIGHT

BODY LENGTH

TAIL LENGTH

BRAIN WEIGHT

grams

mm.

mm.

grams

NXVIf

f

56.7

129

109

1.613

h

f

73.9

148

132

1.666

d

f

66.7

138

112

1.674

b

m

98.3

156

141

1.699

73.9

H3

m

1.663

N XVII f

m

71.8

140

112

1.717

b

m

95.4

155

130

1.718

d

m

125.0

180

150

1.773

h

f

97.7

152

139

1.779

97.5

157

133

1.747

N XVIII b

f

128.5

168

153

1.815

d

f

134.0

163

148

1.870

131.3

166

151

1.843

NXIXc

m

167.6

175

160

1.953

167.6

175

160

1.953

NXXe

f

321.8

230

188

2.008

b

(4)

f

227.0

206

178

2.028

27 4.

218

183

2.018

NXXIf

m

339.4

244

190

2.150

i

f

282.3

216

195

2.162

310.9

230

193

2.156

NXXII

N XXIII a

m

394.0

256

202

2.345

394.0

256

202

2.345

But, according to the authors cited above, the marked difference between the two forms in body size does not appear during the period of rapid growth, but later, so that at maturity the Norway rat has a body weight 25 to 40 per cent above that of the Albino rat of hke age. For the same age however, the percentages of water in the central nervous system is just a trifle higher in the case of the Norway. Relative to the body weight, the Norway rat at maturity has a heavier brain than the albino rat, the difference being about 16 per cent in favor of the Norway.

On the basis of these rough data, the approximate age of the individuals in tables 1 and 2 can be inferred.

To my regret, I did not obtain material under 17 grams in body weight. I could, therefore, not make a complete study of the postnatal growth of the cerebral cortex of the Norway rat from birth on and must in consequence be content to present in this paper the data beginning with material probably from 10 to 12 days old. It may, however, be noted here, that, among the rats trapped, the following were evidently members of the same litter and still following the mother.

(1) NXIa, NXIb, NXIc, N XI d, with their mother N XX a, and three other young which were used for another purpose.

(2) N XI i, N XI h, and four others.

(3) N XIII a, N XIII b, N XIV g, N XIV h, N XIV i, NXIVj,NXIVk.

(4) N XIV e, N XIV f, and two others.

(5) NXIVa, NXIVb, NXIV.c, N XIV d and two others, with their mother N XX b.

This suggests that the Norway rats whose brain weighs less than 1.5 grams or whose body weighs less than about 40 grams are not yet independent of their mothers.

III. TECHNIQUE

For the technique of fixation and imbedding and the making and staining of the sections, the same procedures which have been already described (Sugita, '17 a) were followed. Thirteen different localities were measured on sections in three planes corresponding to those used in the former study of the Albino cortex (cf. figs. 2, 4 and 6 in the paper cited).

As to the cortical cell-lamination of the Norway rat, two sets of figures with explanations were given in the former paper (Sugita, '17 a) reproduced from Lewis (^1881) and Fortuyn ('14) and to those I would like to call attention on this occasion. There does not appear to be any important difference between the Norway and the albino rats in the cell-lamination of the cerebral cortex.

IV. OBSERVED DATA GIVEN IN TABLE AND CHART

As in the case of the albino rat, the measurement of the cortical thickness of the Norway brain was made at the localities I-XIII by the direct measurement of the sections as prepared and was then recorded without correction. The results thus obtained are condensed in table 3.

Table 3 shows for each brain weight group the average thickness of the cerebral cortex of the Norway rat as directly observed in each of the three sections and the general average obtained by averaging the thicknesses of the sagittal, frontal and horizontal sections. The average brain weight corresponding to the average thickness of the cortex is obtained by doubling the weight of the brain, from which the sagittal and frontal sections were taken, adding the weight of the brain from which the horizontal sections were taken, and dividing the sum by three.

Chart 1 is based on table 3 and shows the increase in the general average thickness of the cerebral cortex of the Norway rat,

TABLE 3

Showin.g the general average thickness of the cerebral cortex of the Norway rat according to brain xveight groups, also the average thickness in the sagittal, frontal and horizontal sections. Observations on slide, without correction

BR.«N

SAGITT.VL SECTION

FRONTAL SECTION

HORIZONTAL SECTION

GENERAL AVERAGE

WEIGHT

GROUP

Number

Brain

Thick

Thick

Number

Brain

Thick

Brain

Thick

of cases

weight

ness

ness

of cases

weight

ness

weight

ness

grams

mm.

mm.

grams

m m .

grams

mm.

NXI

3

1.164

1.34

1.43

3

1.164

1.44

1.164

1.40

NXII

NXIII

1

1.369

1.35

1.50

1

1.343

1.50

1.360

1.45

NXIV

6

1.430

1.43

1.48

5

1.447

1.54

1.436

1.48

NXV

2

1.537

1.40

1.50

2

1.520

1.58

1.532

1.49

N XVI

3

1.629

1.41

1.54

4

1.663

1.63

1.640

1.53

NXVII

4

1.739

1.51

1.56

4

1.747

1.59

1.742

1.55

N XVIII

2

1.829

1.51

1.64

2

1.843

1.63

1.834

1.59

NXIX

2

1.972

1,56

1.5S

1

1.953

1.68

1.965

1.61

NXX

2

2.052

1.49

1.48

2

2.018

1.58

2.041

1.52

NXXI

2

2.172

1.53

1.53

2

2.156

1.75

2.166

1.60

NXXII

N XXIII

1

2.345

1.60

1

2.345

1.73

2.345

1.67

THE JOURNAL OF COMPARATIVE NEUROLOGV, VOL. 29, NO. 1

18

NAOKI SUGITA

as directly observed, and without correction and also the average values for the sagittal, frontal and horizontal sections, according to the increase of the brain weight.

V. CORRECTED DATA PRESENTED IN TABLES AND CHARTS

Using the detailed observed values which were all carefully tabulated, although they have not been published, a series of

iO 11 12 J3 14 15 16 IT 18 19 ^0 2t 22 23 J-'

Chart 1 Giving the average thickness of the cortex on slide (not corrected)' in the sagittal, frontal and horizontal sections and the general average thickness

on brain weight group in the Norway rat. Based on table 3. S Average

thickness of the cortex in sagittal section. Measured on slide. F Average

thickness of the cortex in frontal section. Measured on slide. H Average

thickness of the cortex in horizontal section. Measured on slide. • "A General average thickness of the cortex of three kinds of sections. Measured on slide.

correction-coefficients, obtained in exactly the same manner as for the albino rat, were found and applied to the observations on the Norway cortex. The corrected values are those entered in tables 4, 5 and 6. The tables also contain in each case the measurements from which the correction-coefficient was obtained and for each brain weight group the average value of the correction-coefficient for that group.

Table 7 shows the corrected values for the average thickness of the cortex, obtained in the same way as were the uncorrected

GROWTH OF THE CEREBRAL CORTEX

19

TABLE 4 Showing the corrected values of the cortical thickness in the sagittal section for each individual and for each brain weight group. The data for the correction-coefficients are indicated separately for each brain and the coefficient is given loilh the average for each group

CORRECTION

THICKNESS OF

THE CORTEX

BRAIN

COEFFICIENT

(SAGITTAL

section)

BRAIN WEIGHT

GROUP

WEIGHT

Diam.

L. F

on fresh

brain

Diam.

L. F

on slide

Loc. I

Loc. II

Log. Ill

Loc. IV

Loc. V

Avera«e

grams

myn.

m TO .

m m .

TO TO.

mm.

mm.

mm.

mm.

NXIb

1.155

11.75

10.40

2.18

1.73

1.44

1.21

1.05

1.52

a

1.160

12.10

10.15

2.40

1.83

1.63

1.32

1.07

1.65

i

1.175

12.55

9.80

2.61

1.83

1.61

1.26

1.04

1.67

i.m

1.

20

2.40

1.80

1.56

1.26

1.05

1.61

NXII

N XIII a

1.369

12.95

10.10

2.47.

1.87

1.72

1.33

1.27

1.73

1.369

1.

28

2.47

1.87

1.72

1.33

1.27

1.73

NXIVb

1.407

13.45

10.50

2.76

2.04

1.73

1.59

1.36

1.90

g

1.429

13.05

10.10

2.56

1.82

1.72

1.40

1.32

1.76

a

1.431

13.15

10.40

2.64

2.01

1.82

1.56

1.34

1.87

i

1.431

13.05

10.25

2.56

1.90

1.71

1.48

1.31

1.79

e

1.437

12.80

10.05

2.47

1.87

1.73

1.40

1.24

1.74

k

1.445

13.35

10.30

2.83

2.03

1.78

1.64

1.38

1.93

14^0

1.

28

2.64

1.95

1.75

1.51

1.33

1.84

NXVc

1.517

12.70

10.10

2.56

1.92

1.72

1.38

1.20

1.76

e

1.557

13.75

10.25

2.83

1.93

1.72

1.49

1.44

1.88

1.537

1.

30

2.70

1.93

1.72

1.44

1.32

1.82

NXVIa

1.619

13.50

10.25

2.68

2.04

1.77

1.46

1.34

1.86

g

1.632

13.45

10.00

2.86

2.17

1.84

1.53

1.21

1.92

e

1.636

13.55

10.10

2.73

1.98

1.77

1.49

1.31

1.86

1.629

1.

33

2.76

2.06

1.79

1.49

1.29

1.88

N XVII e

1.710

13.70

10.50

2.84

2.09

1.95

1.55

1.42

1.97

g

1.721

13.40

10.35

2.78

2.13

1.98

1.63

1.38

1.98

a

1.738

13.60

10.70

2.72

2.00

1.76

1.40

1.21

1.82

c

1.788

14.20

11.20

2.93

2.15

1.92

1.65

1.33

2.00

1.739

1.

29

2.82

2.09

1.90

1.56

1.34

1.94

N XVIII c

1.825

14.30

10.85

2.91

2.07

1.88

1.49

1.28

1.93

a

1.833

14.20

11.50

2.89

2.06

1.69

1.51

1.48

1.93

1.829

1.27

2.90,

2.07

1.79

1.50

1.38

1.93

20

NAOKI SUGITA

TABLE 4— Continued

CORRECTIONCOEFFICIENT

thickness op the cortex (sagittal section)

GROUP

WEIGHT

Diam.

L.F

on fresh

brain

Diam.

L.F

on slide

Loc. I

Loc. II

JLoc. Ill

Loc. IV

Loc. V

Average

grams

mm.

v\ m .

mm.

mm.

vim.

mrn.

mm.

mm.

N XIX b

1.962

14.70

11.50

2.98

2.12

1.97

1.54

1.46

2.01

a

1.981

14.40

11.50

2.83

2.08

1.75

1.54

1.44

1.93

1.972

1.

26

2.91

2.10

1.86

1.54

i.45

1.97

NXXc

2.015

14.55

11.50

2.86

2.00

1.81

1.55

1.43

1.93

a

2.089

14.95

12.00

2.75

1.93

1.67

1.34

1.30

1.80

2.052

1.

25

2.81

1.97

i.74

1.45

i.ST'

1.87

NXXIg

2.156

15.15

11.90

3.01

2.15

1.82

1.58

1.40

1.99

d

2.187

15.30

11.50

2.94

2.09

1.85

1.60

1.41

1.98

2.172

1.

30

2.98

^..?^

1.84

1.59

/.4i

^.SS

NXXII

N XXIII a

2.345

14.50

12.50

2.74

2.07

1.75

1.38

1.33

1.86

2.345

1.16

2.74

2.07

1.75

1.38

1.33

.1.86

values shown in table 3. This table (table 7) serves as a standard for discussing the actual thickness of the fresh cortex of the Norway rat. The average thickness in the adult Norway rat is 2.06 mm., as obtained by averaging the thicknesses of the cortex in Groups N XV-N XXIII, in which stages the cortex may be considered to have reached its full thickness.

Charts 2 to 7 show graphically the data given in tables 4 to 6 respectively, and chart 8, which is based on table 7 giving the average values, presents a general picture of the growth changes in the cortex according to brain weight.

Charts 2, 4 and 6 show the individual determinations for the thickness of the cortex in the sagittal, frontal and horizontal sections, respectively, plotted according to the brain weight. Chart 2 gives the individual records for locality I and locality V with the average for all localities from I to V in the sagittal sections. In a like manner, chart 4 gives the values for localities VIT and VIII with the average of localities VI to VIII for the

GROWTH OF THE CEREBRAL CORTEX

21

TABLE 5

Showing the corrected values of the cortical thickness in the frontal section for each individual and for each brain weight group. The data for the correction-coefficients are indicated separately for each brain and the coefficient is given with the average for each group

COEFFICIENT

thickness of the cortex (frontal section)

BRAIN ■^EIGHT

BRAIN WEIGHT

GROUP

Diam. W. D

on fresh brain

Diam. W. D on slide

Loc. VI

Log. VII

Loc. VIII

Average

grams

7nm.

Tnm.

m7n.

mm.

mm.

mm.

NXIb

1.155

13.00

9.90

2.05

2.11

1.68

1.95

a

1.160

12.70

10.00

1.94

1.92

1.62

1.83

i

1.175

12.50

9.20

1.96

1.99

1.62

1.86

1.164

1.

31

1.98

2.01

1.64

1.88

NXII

N XIII a

1.369

13.00

10.00

2.07

2.21

1.59

1.96

1.369

1.

30

2.07

2.21

1.59

1.96

NXIVb

1.407

13.05

9.90

2.27

2.13

1.71

2.04

g

1.429

13.20

9.50

2.18

2.29

1.71

2.06

a

1.431

12.85

10.70

2.04

2.00

1.73

1.92

i

1.431

13.40

10.30

1.90

2.06

1.57

1.84

e

1.437

13.25

9.80

1.89

2.13

1.56

1.86

k

1.445

13.30

9.90

2.12

2.15

1.65

1.97

1.430

1.32

2.07

2.13

1.66

1.9S

NXVc

1.517

13.20

10.00

1.98

2.21

1.62

1.94

e

1.557

13.50

9.60

2.28

2.39

1.76

2.14

1.537

/.

36

2.13

2.30

1.69

2.04

NXVIa

1.619

13.80

10.80

2.01

2.13

1.72

1.95

g

1.632

13.70

9.90

2.24

2.57

1.83

2.21

e

1.636

13.80

10.00

2.14

2.36

1.75

2.08

1.629

1.

35

2.13

2.35

1.77

2.08

N XVII e

1.710

13.80

10.00

2.15

2.31

1.68

2.05

g

1.721

13.60

10.40

2.20

2.35

1.75

2.10

a

1.738

14.10

10.60

2.01

2.17

1.66

1.95

c

1.788

13.95

10.60

2.35

2.40

1.82

2.19

1.739

1.

33

2.18

2.31

1.73

2.07

N XVIII c

1.825

14.45

10.70

2.20

2.35

1.73

2.09

a

1.833

13.95

11.70

2.18

2.22

1.80

2.07

1.829

1.27

2.19

2.29

1.77

2.08

22

NAOKI SUGITA

TABLE 5— Concluded

BRAIN WEIGHT

BRAIN WEIGHT

GROUP

grams

NXIXb

1.962

a

1.981

1.972

NXXc

2.015

a

2.089

2.052

NXXIg

2.156

d

2.187

2.172

NXXII

N XXIII

COEFFICIENT

Diam.W'.D

on fresh brain

14.60 13.95

T>is.m.W. D on slide

11.60 10.80

1.26

14.30 14.50

10.50 11.20

1.33

14.75 15.05

11.10 10.80

1.36

thickness of the cortex (frontal section)

Loc. VI Loc. VII

2.08

2.04 2.06

2.14 1.80 1.97

2.03 2.19 2.11

2.28 2.21 2.25

2.32

2.08 2.20

2.24 2.54

2.39

Loc. VIII

1.68 1.72 1.70

1.73 1.66 1.70

1.69 1.77 1.73

Average

2.01 1.99 2.00

2.06 1.85 1.96

1.99 2.17

2.08

frontal sections. Chart 6 does the same for locahties IX and XIII with the average of localities IX to XIII in the horizontal sections. Charts 3, 5 and 7 show the average values of the cortical thickness in the sagittal, frontal and horizontal sections, for each brain weight group. Further, on each chart is shown the change in thickness at each one of the localities measured in that section.

Chart 8 is based on table 7 and shows the general average (corrected) thickness of the cerebral cortex of the Norway rat according to the brain weight and also the average thickness in each of the sections.

VI. DISCUSSION

The relations existing between each of the several localities measured in this study of the Norway are quite similar to the relations found in the cerebral cortex of the albino rat. Individual variations appear, but these are no higher than ±6 per cent, compared with the average values of the group. No sex differ

GROWTH OF THE CEREBRAL CORTEX

23

TABLE 6

Showing the corrected values of the cortical thickness in the horizontal section for each individual and for each brain weight group. The data for the correctioncoefficients are indicated separately for each brain and. the coefficient is given with the average for each group

BRAIN WEIGHT GROUP

NXI d

h c

NXII

N XIII b

X XIV c

h

J f d

NXVb d

NXVIf

h d b

NXVII f b d h

N XVIII b d

BRAIN WEIGHT

1.133 1.160 1.199 1.164

1.343

1.S4S

1.407 1.428 1.443

1.475 1.4S1 1.447

1.511 1.529 1.520

1.613 1.666 1.674 1.699 1.663

I. in

1.718 1.773 1.779 i.747

1.815 1.870 1.843

COEFFICIEXT

Diam. W. B on

fresh brain

13.80 13.80 13.90

Diam.

W.B

on slide

11.00 10.10 10.80

30

14.20 10.30 1

14.20 14.35 14.35 14.55 14.60 1.

14.65 14.50

1 .

10.60 10.70 10.50 10.90 10.25

10.10 10.50

41

14

90

15.00 j

15

15

14

75

11.00 10.95 11.30 11.05

1.35

15.45 14.60 15.10 15.40

1.

15.00 15.40

1.

11.45 11.30 10.75 11.35

35

11.00 10.85

Loc. IX

2.52 2.85 2,52 2.63

2.91 2.91

2.57 3.19 2.96 2.92 2.91 2.91

3.19 3.11

3.15

3.25 2.95 2.93 3.33

3.12

2.89 2.73

2.77 3.27 2.92

3.06 3.60

3.33

THICKNESS OF THE CORTEX (HORIZON r.\L SEr;TION)

Loc. X

1.91 1.99 1.84 1.91

2.02

2.02

2.06 2.14 2.22

2.08 2.22 2.14

2.32 2.21

2.27

2.34 2.23 2.14 2.36

2.27

2.18 2.17 2.23 2.31

2.22

2.21

2.38 2.30

XI

1.72 1.92 1.75 1.80

2.03

2.03

1.93

2.08 2.24 2.03

1.88 2.03

2.15 2.12

2.14

2.10 2.22 2.12 1.92

2.09

2.16 2.04 2.13 2.18

2.13

2.08 2.14

2.11

Loc. XII

1.56 1.69 1.62 1.62

1.85 1.85

1.72 1.82 1.95 1.81 1.74 1.81

1.97 1.91

1.94

1.96 1.94 1.85 1.76 1.88

1.93 1.80 1.84 2.02 1.90

Loc. XI IJ

1.31 1.50 1.33

1.38

1.57

1.57

1.48 1.57 1.69 1.55 1.56 1.57

1.78 1.62 1.70

1.66 1.76 1.52 1.48 1.61

1.62 1.41 1.51 1.72

1.57

1.84 1.57 1.96 1.76 1.90 1.67

.A verage

1.80 1.99 1.81 1.87

2.08 2.08

1.95 2.16 2.21 2.08 2.06 2.09

2.28 2.19

2.26 2.22 2.12 2.17 2.19

2.16 2.03 2.10 2.30

2.15

2.15 2 37

24

NAOKI SUGITA

TABLE 6— Concluded

BRAIN WEIGHT

COEFFICIEXT

THICKXESS OF THE CORTEX (HORIi,OXT.U. section)

BRAIN WEIGHT GROUP

Diam. W. B on

fresh brain

Diam. W. B

on slide

Loc. IX

Loc. X

Loc. XI

Lof. XII

Loc. XIII

Average

grams

m m .

m m .

m VI .

711 m.

mm.

mm.

mm..

mm.

NXIX c

1.953

15.65

11.70

3.14

2.17

2.14

2.01

1.81

2.25

1.95S

1.34

3.U

2.17

2.14

2.01

1.81

^.^5

NXXe

2.008

15.55

11.90

3.10

2.28

2.09

1.87

1.52

2.17

b

2.028

15.85

12.00

2.78

2.05

1.97

1.71

1.43

1.99

2.018

1.31

1

2.H

2.17

2.03

1.79

i.4S

2.08

NXXIf

2.150

16.55

12.10

3.30

2.66

2.22

1.94

1.57

2.34

J

2.162

16.25

12.40

3.60

2.38

2.16

1.98

1.57

2.34

2.156

1.34

1

3.45

2.52

2.19

1.96

1.57

^.54

NXXII

N XXIII a

2.345

16.55

12.90

3.14

2.58

2.17

1.69

1.54

2.22

2.3j^5

1.28

3.14

2.58

2.17

1.69

i.54

2.22

ence in cortical thickness is recognizable when the brain weights are similar.

In the sagittal sections, the cortex attains nearly its full thickness when the brain weighs 1.63 grams (Group N XVI), while in the frontal and horizontal sections, this is attained somewhat earlier, that is, in the brains weighing 1.53 grams (Group N XV) (cf. charts 3, 5, 7, 8). In the general average thickness of the cortex of the Norway rat, the full thickness is attained in the brains w^eighing about 1.53 grams, at which phase the body weight observed is about 55 grams (tables 1 and 2) (chart 8). In the full grown Norway rat at brain weights between 1.6 and 2.4 grams, the average cortical thickness ranges between 1.97 and 2.14 mm., with a mean value for Groups N XVI-N XXIII (table 7) of 2.06 mm. The average thickness for each locality is given in table 8 for the Norway rat, together with the corresponding values for the Albino, thus making it possible to compare the cortical thickness in the two forms.

GROWTH OF THE CEREBRAL CORTEX

25

TABLE 7

Showing the average corrected thickness of the cerebral cortex in the Norway rat for each brain weight group.

SAGITTAL

SECTION

FRONTAL

HORIZONTAL SECTION

GENER.\L

.AVERAGE

BRAIN WEIGHT

Brain

weight

Thickness

Thickness

Brain weight

Thickness

Brain weight

Thickness

grams

mm.

mm.

grams

mm.

grams

mm.

NXI

1.164

1.61

1.88

1.164

1.87

1.164

1.79

NXII

N XIII

1.369

1.73

1.96

1.343

2.08

1.360

1.92

NXIV

1.430

1.84

1.95

1.447

2.09

1.436

1.96

NXV

1.537

1.82

2.04

1.520

2.24

1.532

2.03

NXVI

1.629

1.88

2.08

1.663

2.19

1.640

2.05

NXVII

1.739

1.94

2.07

1.747

2.15

1.742

2.05

N XVIII

1.829

1.93

2.08

1.843

2.26

1.834

2.09

NXIX

1.972

1.97

2.00

1.953

2.25

1.965

2.07

NXX

2.052

1.87

1.96

2.018

2.08

2.041

1.97

NXXI

2.172

1.99

2.08

2.156

2.34

2.166

2.14

NXXII

N XXIII

2.345

1.86

2.345

2.22

2.345

2.04

Within the limits of our material, the course of development of the cortical thickness in every locality seems, in general, similar to that in the corresponding locality of the albino rat, the descriptions of which were given in the former paper (Sugita, '17 a, pp. 574-577).

VII. A COMPARISON OF THE NORWAY RAT WITH THE ALBINO RAT IN RESPECT OF CORTICAL THICKNESS

The main object of the present paper is to compare the data from the Norway with those from the albino rat, in respect of the cortical thickness, a comparison of much interest, since the two forms are so closely related genetically and at the same time show differences in body size and in absolute brain weight which have been already noted.

Comparing the mature brains, which weigh alike, of the both forms (table 8), the Norway cortex, whose thickness on the average in Groups NXVI to NXX (brain weight average 1.844 grams) is 2.05 mm., surpasses by 0.15 mm. or 8 per cent the albino cortex, whose thickness on the average in Groups XVI to XX

26

NAOKI SUGITA

(brain weight average 1.815 grams) is 1.90 mm. Here the albino cortex is taken as the standard for the determination of the percentage difference. For the comparison of each locaUty and the averages of each section, table 8 is to be consulted. It is remarkable that both in the sagittal and horizontal sections the

12 JO

Z8 Z6 2+

aj

10 48

i.b

1412 10 aS a6

+ Oi

.

,

-.

.

.

•

'.

•

.

.'.

"

•

.

•

••

•

.

'<

—

—

10 H 12 1.5 1+ 15 16 17

19 2,0 2,1 22 23 2+ fs.

Chart 2 Giving the corrected thickness of the cerebral cortex of the Norwayrat in the sagittal section. Individual entries for the cortical thickness at localities I and V, and the average thickness of the sagittal section (localities I, II, III, IV and V) are given. Based on table 4. ° Cortical thickness at locality I. Corrected. ^ Cortical thickness at locality V. Corrected. • Average thickness of the sagittal section. Corrected.

percentage differences follow in the same order from the frontal to the occipital pole, rising towards the occipital pole.- The occipital parts, represented by the pair of localities V and XIII, are the most developed in the Norway, surpassing the corresponding parts of the Albino by 15 and 28 per cent respectively. The pair of localities IV and XII, whose positions are adjoining, show also a marked excess in thickness, that is, 10 and 11 per cent

GROWTH OF THE CEREBRAL CORTEX

27

respectively. The only other large difference is 15 per cent at locality VI.

Accordingly, in the mature rats, the average thicknesses in the sagittal, frontal and horizontal sections are respectively 6.7, 9.1

1

J

^—

-

y^

^x

-'-

'"

^ 1

__/

...-.,

-,i

'ZJ

"^^

.,^

^

■~^s

l^-^-..

^

--.

--'

^ '

-i« 

1

—

7'\

'"

—

■"'^■

-

--

--

-v

^■"

j

i

1

i 1

2 1

3 1

+ 1

5 J

6 1

r 1

8 1

9 2

2

1 2

2 2

3 'it

t r

Chart 3 Giving the average thickness of the cortex for each brain weight group at localities I, II, III, IV and V in the sagittal section and the average thickness at five localities in each brain weight group in sagittal section. Based on table 4. ■ — • — • — (above the heavy line) Cortical thickness at locality I.

Corrected. (above the heavy line) Cortical thickness at locality II.

Corrected. • — ■ — • — (near the heavy line) Cortical thickness at locality III.

Corrected. (below the heavy line) Cortical thickness at locality IV.

Corrected. (below the heavy line) Cortical thickness at locality V.

Corrected. • 'S Average thickness of the sagittal section by each brain

weight group.

and 8.0 per cent greater and the general average thickness is, consequently, 8 per cent greater in the Norway than in the albino rat, while the brain weights are almost the same (about 1.8 grams) .

As regards the differences in cortical thickness here found a few comments may be made. Possibly all of the larger differ

28

NAOKI SUGITA

1

1

.

.

.•

•.

/

%

■.

t

•

•

.

■\

^

—

—

—

—

10 1.1 12 13 M is J6 17 18 19 20 21 22 %"■

Chart 4 Giving the corrected thickness of the cerebral cortex of the Norwayrat in the frontal section. Individual entries for the cortical thickness at localities VII and VIII, and the average thickness of the frontal section (localities VI, VII and VIII) are given. Based on table 5. ° Cortical thickness at locality VII. Corrected >< Cortical thickness at locality VIII. Corrected. • Average thickness of the frontal section. Corrected.

,

-~

—

—

^ /

/

^-'

T..-

^.Z'

"^

^'^

'

-^

■-<-'

^__

-^

' ~~

'" —

1

«« 

10 11 12 13 14 15 16 17 18 . 19 20 21 U ^^

Chart 5 Giving the average thickness of the cortex for each brain weight group at localities VI, VII and VIII in the frontal section and the average thickness at three localities for each brain weight group in frontal section. Based on table 5.

Cortical thickness at locality VI. Corrected. Cortical

thickness at locality VII. Corrected. Cortical thickness at locality VIII.

Corrected. • 'F Average thickness of the frontal section by each brain

weight group.

ences noted may be correlated with differences in function, but at present we shall consider only those which appear in the occipital cortex, that is, at localities IV, V, XII, and XIII. There is reason to think that the eye and the visual apparatus in general are less well developed in the Albino than in the Norway rat.

Chart 6 Giving the corrected thickness of the cortex of the Norway rat in the horizontal section. Individual entries for the cortical thickness at localities IX and XIII and the average thickness of the horizontal section (localities IX, X, XI, XII and XIII) are given. Based on table 6. ° Cortical thickness at locality IX. Corrected. ^ Cortical thickness at locality XIII. Corrected. • Average thickness of the horizontal section. Corrected.

The visual cortex of the rat is at the occipital end of the brain (Ferrier, '86) and would probably be underdeveloped in the Albino in which vision was less perfect. The relatively less thickness of the cortex in the localities IV, V, XII and XIII in the Albino brain would therefore fit with the diminished visual function in this form.

If, during the growing period, a comparison of cortical thickness in brains of Hke weight is made, the result is somewhat puzzling, as seen in chart 9, which gives the thickness of the cortices of the Norway and the albino rats in brains of the same weight.

^

'\

•^-.n

1

1

_^

^

V^

■^~

^m

Chart 7 Giving the average thickness of the cortex for each brain weight group at localities IX, X, XI, XII and XIII in the horizontal section and the average thickness at five localities in each brain weight group in horizontal section. Based on table 6. (above the heavy line) Cortical thickness at locality

IX. Corrected. — • — • — (above the heavy line) Cortical thickness at locality

X. Corrected. Cortical thickness at locality XI. Corrected.

(below the heavy line) Cortical thickness at locality XII. Corrected.

(below the heavy line) Cortical thickness at locality XIII. Corrected.

• •!! Average thickness of the horizontal section for each brain weight group.

Generally the cortical thickness of the Norway rat, whose brain weighs more than 1.3 grams, is clearly higher than that of the albino rat of like brain weight, while in brains weighing less than 1.2 grams the relation is reversed. This seems surprising, but

has its reason,. If the data are treated as follows, which seems to me quite a rational treatment, the reason will be disclosed." The brain of the Norway rat at birth weighs usually somewhat more than that of the newborn albino rat, and the final brain weight in the full grown Norway is ca. 2.5 grams or 25 pe*r cent higher than that in the mature albino rat of like age, which weighs about 2.0 grams. As already shown by Donaldson and

Chart 8 Giving the corrected thickness of the cortex in the sagittal, frontal and horizontal sections and the general average thickness for each brain weight group. Based on table 7. Nbrway rat. • — • — ■ — S Average thickness of the

cortex in sagittal section. Corrected. F Average thickness of the cortex in

frontal section. Corrected. H Average thickness of the cortex in

horizontal section. Corrected • "A General average thickness of the cortex

of three kinds of sections. Corrected.

Hatai ('11), the span of life is probably the same in both the forms, extending to about three years. So, if throughout this span of life the developmental course of the brains was quite similar for both forms, the brains which have like weights would not represent the same stage of the development, but on the contrary, a brain of the Norway rat would be under these conditions, in a younger stage.

Table 9 gives the percentage of water in the brains of the Norway and of the albino rats. The comparison of the data of the

TABLE 8

A comparison of the cortical thicknesses at each locality ayid on the average, in the adult Norway and the albino brains of the same absolute weight. The measurements used here are average values of Groups N XVI-N XX and Groups XVI-XX respectively, taken from tables 4 to 6 of this paper and tables 6 to 8 (Sugita, '17a). The Gorresponding brain iveights are 1.844 grams in the Norway and 1.815 grams in the Albino. The thickness of the Albino cortex is ahoays taken as the standard for computing the percentage differences

THICKNESS OF

THE CORTEX

CORTEX OP THE

SECTIONS

LOCALITIES

NORWAY R.\T EX

Norway rat

Albino rat

CEEDS BT

■mvi.

mm.

per cent

Locality I

2.84

2.80

1.4

II

2.06

1.92

7.3

Sagittal

III

1.82

1.74

4.6

IV

1.51

1.36

10.0

V

1.37

1.19

15.1

Average

1.92

1.80

6.7

Locality VI

2.11

1.84

14.8

Frontal

VII

2.28

2.18

4.6

VIII

1.73

1.59

8.9

Average

2.04

1.87

9.1

Locality IX

3.09

3.08

0.3

X

2.23

2.06

8.2

Horizontal

XI

2.10

2.04

3.0

XII

1.90

1.71

11.1

XIII

1.63

1.27

28.3

Average

2.19

2.03

8.0

General avers

lore

2.05

1.90

8.0

two forms is made so as to bring those of approximately the same age on the same hue of the table. It will be seen by these comparisons that the Norway rat brain, if paired with the albino rat brain of like age, shows almost the same value of the percentage of water, while the brain weight differs by 16 to 20 per cent in favor of the Norway rat brain, the weight of the Norway brain being taken as the standard.

So, from the point of view of age, a Norway rat brain should be in the same phase of development with an albino brain,

GROWTH OF THE CEREBRAL CORTEX

33

TABLE 9

Giving the percentage of water in the brain of the Norway and of the albino rats of the same age. The comparison of the data of the two forms is made so as to bring those of approximately the same age on the same line of the table. Based principally on tables 10 and 12, given by Donaldson and' Hatai {'11) on pp. 439-443, Jour, of Comp. Neur., vol. 21

STORWAY RAl

(males)

ALBINO RAT (mALES) OF LIKE

AGE

AGE

BODY WEIGHT OBSERVED

BRAIN WEIGHT

PERCENTAGE OP WATER ON BRAIN

BODY WEIGHT

CALCULATED

BRAIN

WEIGHT

CALCULATED

LESS THAN

NORWAY

BRAIN

Observed

Calculated

WEIGHT

days

grafns

grams

per cent

per cent

grams

grams

per cent

1

5.1

0.2361

88.2

88.00

4.7

0.217

8

10

12.2

0.859

86.9

87.05

11.8

0.840

2

13

18.1

1.245

85.3

85.39

14.9

1,011

19

15

17.7

1.195

84.5

84.58

16.1

1.057

12

16

26.1

1.368

82.8

84.19

16.7

1.077

21

19

25.5

1.423

81.5

83.12

18.7

1.131

21

25

32.6

1.498

80.9

81.39

23.9

1.237

17

40

35.83

1.525

79.2

79.39

42.5

1.434

6

47

38. 5»

1.522

79.3*

79.24

54.1

1.507

1

106

68.63

1.878

78.4

78.50

174.0

1.830

3

200.0

2.152

78.7

78.59

160.0

1.807

16

215.0

2.17

78.8

78.53

170.0

1.824

16

231.0

2.20

78.6

78.45

180.0

1.838

16

248.0

2.23

78.7

78.38

190.0

1.854

17

267.0

2.25

78.2

78.32

200.0

1.866

17

287.0

2.28

78.2

78.24

210.0

1.879

18

308.0

2.31

78.9

78.18

220.0

1.890

18

331.0

2.33

78.2

78.12

230.0

1.903

18

355.0

2.33

78.3

78.11

240.0

1.913

19

380.0

2.38

78.2

78.10

250.0

1.923

19

406.0

2.41

78.0

78.06

260.0

1.933

19

434.0

2.43

78.2

77.96

270.0

1.944

20

463.0

77.9

77.50

280.0

1.954

494.0

78.0

290.0

525.0

78.0

300.0

^ The data given in this column below this entry are based on unpublished observations of Donaldson and Hatai, the records of which are kept in the Wistar Institute.

- The data given in this column below this entry were obtained by calculation according to body weight.

3 As the result of confinement, the body growth in the Norway is remarkably retarded.

THE JOURNAL OF COMPAR.\TIVB NEUROLOGY, VOL. 29, NO. 1

34

NAOKI SUGITA

which weighs 16 to 20 per cent less. With this relation in view, I reduced by 18 per cent — which is the mean value of 16 to 20 per cent (see table 9) — the weight of the Norway rat brains in table 7, and assumed that I thus obtained brain weights which represent the corresponding brain weights of the albino ra,'t in respect to the cortical development. I have plotted the values for the actual cortical thickness on the reduced brain weights by

•

0.1 0.2 0.3 0.4 0.5 Q6 0.7

0.9 1.0 1.1 1.2 1.3 1.4 L5 16 1.7

19 20 Z\ 2.2 2.3 J« 

Chart 9 Giving a comparison of the thickness of the Norway cortex with that

of] the albino cortex, on brain weight. • 'N General average thickness of the

Norway cortex according to the actual brain weight group. AL General

average thickness of the Albino cortex according to the brain weight group. Smoothed. Taken from chart 9 of the second paper of this series. • — • — • N' General average thickness of the Norway cortex entered according to the reduced brain weight representing the albino brain weight of the corresponding age.

the dot and dash line in chart 9, in which the smoothed graph for the cortical thickness of the albino rat is represented by a dotted Une. Glancing at the chart, my assumption appears to be justified as both the graphs for the reduced Norway and the Albino are found to run a similar course. This relation is acceptable, since, as shown in the tables given by Donaldson and Hatai ('11), and also by Miller ('11), the relative weight of the brain in the mature albino rat is 12 to 16 per cent less than in the Norway rat of like body weight, and, furthermore, the relative weight of the

GROWTH OF THE CEREBRAL CORTEX 35

body in the Albino is about 20 to 40 per cent less than in the Norway rat of like age (table 9). Accordingly, the albino brain should be about 18 per cent or more, less than the Norway brain of like age, and the data for the thickness of the cortex in the two forms show a fairly constant relation, when plotted as in chart 9 in accordance with this assumption (see also table 3, Sugita, '17 a).

As stated, Norway rats under about 10 days of age have not been studied, but a comparison of the graph for the thickness of the cortex in the normal albino rat with the graph for the Norway cortex displaced for age makes it reasonable to assume that a Norway brain which weighs 1.16 grams (Group N XI) corresponds to an albino brain which weighs about 0.95 grams (Group IX), at which stage the cerebral cortices of the both forms have nearly completed their active growth in thickness and are going over to the second phase, during which the cortical area keeps pace with the increase in brain volume. It may be assumed also (see later) that, in the Norway rat, with a brain weight of about 1.4 grams the cortical myelination is beginning to take place.

Thus in the postnatal life of the Norway rat, the first phase of the development of the cerebral cortex covers the period during which the brain weight increases to 1.16 grams from birth, when the brain weight is about 0.25 grams, and the second phase of the cortical development covers the period, during which the brain weight increases from 1.16 grams to about 1.44 (Group N XIV) when the cortex attains within 4 per cent the full thickness. By the middle of the second phase the process of myelination is active, and before the end of this phase the cortex has already attained nearly its full thickness.

This assumption, that the completion of the cortical development in thickness coincides with the period of active myelination, is supported by another set of facts. Table 10 gives the absolute weights of the dry substance in the brain of the Norway rat, arranged according to brain weight. These values were calculated by me from tables originally given by Donaldson and Hatai ('11). The data are plotted in chart 10, which also gives the corresponding data for the albino rat, in a dotted curve.

36

NAOKI SUGITA

TABLE 10

Giving the weight of the dry substances in the brain of the Norway rat according to brain weight. Based on the observed data given by Donaldson and Hatai {'11), in p. 448, Jour. Camp. Neur., vol. 21. Both sexes averaged. *Males only.

WEIGHT OF THE

WEIGHT OF THE

TOTAL BRAIN WEIGHT

DRY SUBSTANCES IN

TOTAL BR.UN WEIGHT

DRY SUBSTANCES IN

THE BRAIN

THE BRAIN

grams

grams

grams

grams

0.25

0.041

1.55

0.309

0.35

1.65

0.339

0.45

1.75

0.377

0.55

1.85

0.400

0.65

0.067*

1.95

0.407

0.75

0.100

2.05

0.445

0.85

0.100

2.15

0.460

0.95

2.25

0.498

1.05

2.35

0.500

1.15

0.155

2.45

0.540

1.25

0.210

2.55

0.534

1.35

0.229

2.65

0.575

1.45

0.291

2.75

0.600*

Q6

1

/

as

/

r^

y

/

01+

J

V

,/

as

/}

'^

az

'/

..•'

l>.

ai

■<^

^

^

^

y

^"'

02 a4 06

10 tZ W M> 18 ZO II 24 26 2,8 /«.

Chart 10 Giving the absolute weights of the dry substance in the -Norway brain, arranged according to brain weight, based on the observations of Donaldson and Hatai ('11), accompanied by the corresponding data for the albino rat, in a dotted line. ^ and * show the turning points of the curves.

GROWTH OF THE CEREBRAL CORTEX 37

This chart shows clearly that the solids in the Norway brain increase rapidly after the brain weight has reached something more than 1.2 grams (see x). This turning point of the graph corresponds to 0.95 grams of brain weight in the Albino (see *). It was found in the albino rat that, when the brain weight has surpassed 1.15 grams, namely 0.95 plus 0.20 grams, myelination of the cortical fibers is active. Hence, in the Norway brain, the myelination in the cortex should be active when the brain weight has reached 1.44 grams, namely somewhat more than 1.2 plus 0.2 grams. Furthermore, as we have seen that in the albino rat the beginning of myelination in the cortex coincides with the phase when the cortex has nearly attained its full thickness, so we see the same relations in the Norway rat also.

From these facts we conclude that the brains of the both forms pass through the same course of cortical development according to age, as the span of life is the same in the two. The weights of the brains which are in the same stage of development, are however not the same in the both forms, being in the Norway rat about 18 per cent — the Norway brain weight being taken as the standard — heavier than in the albino rat. The statement of Donaldson which was expressed in the paper cited, to wit: "If in the animals compared the brain weights are the same, then the Norway rat has a smaller body weight and a higher percentage of water in the central nervous system," might be rewritten as follows : When ages are the same, the Norway rat has a greater body weight, a heavier brain (18 per cent more in weight), a tlTicker cortex and nearly the same percentage of water in the central nervous system.

A comparison of the cortical development in the two forms can be made adequately only by first reducing by 18 per cent the actual brain weight of the Norway rat and then comparing the cortex in both forms according to the corrected brain weight. Since mature Norway brains have only a slightly greater volume than the Albino brains of Uke weight (see table 4 A, Sugita, '18), but at the same time have a cerebral cortex on the average 8 per cent thicker, it follows that in the Norway brain the proportion of gray substance is greater. This difference apparently accounts for the higher percentage of water found in the Norway brain.

38 NAOKI SUGITA

VIII. SUMMARY

1. The thickness of the cerebral cortex of the Norway rat has been systematically investigated, employing as material 36 males and 18 females, all over 17 grams in body weight, and using uniformly the methods w^hich were adopted by me for the investigation of the cerebral cortex of the albino rat.

2. The observed data are first given and later are corrected to the values for the fresh condition of the material. The corrected data are given fully in tables and in charts.

3. The relations of the cortical thicknesses at the several localities measured are quite similar among themselves to those found in the albino rat. The average thickness of the cortex in the adult Norway rat is always higher (1 to 28 per cent) than that of the corresponding locality in the adult albino rat. The occipital cortex is better developed (thicker) in the Norway rat. This is to be associated with the more perfect visual apparatus in the Norway rat.

4. As to the phases of development of the cortical thickness, a Norway brain of a given age corresponds to an albino brain, which weighs about 16 to 20 per cent less. The Norway brain weighing 0.25 to 1.16 grams (Groups N II to N XI) is in its first phase of active development which corresponds to an Albino brain weighing 0.25 to 0.95 grams. The Norway brain weighing 1.16 to 1.44 grams (Groups N XI to N XIV) is in its second phase of development of the cortex corresponding to the albino brain weighing 0.95 to 1.15 grams.

5. The cortex of the Norway rat attains nearly its full thickness at th-e time when the brain weighs somewhat more than 1.44 grams, corresponding to the age of twenty days and to a body weight of something more than 36 grams. At this phase probably the rapid myelination of the fibers in the cerebral cortex is taking place.

6. The general average thickness of the cortex in the mature Norway rat is 2.06 mm., exceeding by about 8 per cent that of the albino rat brain of the same weight.

GROWTH OF THE CEREBRAL CORTEX 39

7. Owing to the greater thickness of the cerebral cortex the mature Norway brain contains more gray matter than does the albino brain of like weight and this excess of gray matter explains the somewhat higher percentage of water found in the Norway brain.

LITERATURE CITED

Donaldson, H. H. and Hatai, S. 1911 A comparison of the Norway rat with the albino rat in respect to body length, brain weight, spinal cord weight and the percentage of water in both the brain and spinal cord. Jour. Comp. Neur., vol. 21, pp. 417-458.

Donaldson, H. H. 1915 The Rat. Memoirs of The Wistar Institute of Anatomy and Biology. No. 6.

Ferrier, David 1886 The functions of the brain. 2nd ed. Smith, Elder & Co., London, pp. 261-262.

FoRTUYN, A. B. D. 1914 Cortical cell-lamination of the hemispheres of some rodents. Arch. Neurol., Path. Lab. London County Asyl., vol. 6, pp. 221-354. Mus decumanus (Pall), p. 260.

Lewis, Bevan 1881 On the comparative structure of the brain in rodents. Phil. Trans., 1882, pp. 699-749.

Miller, Newton 1911 Reproduction in the brown rat (Mus norvegicus). Am. Naturalist, vol. 45, pp. 625-635.

Sugita, Naoki 1917 a Comparative studies on the growth of the cerebral cortex. II. On the increases in the thickness of the cerebral cortex during the growth of the brain. Albino rat. Jour. Comp. Neur., vol. 28, pp. 495 510.

SuGiTA, Naoki 1918 Comparative studies on the growth of the cerebral cortex. III. On the size and shape of the cerebrum in the Norway rat (Mus norvegicus) and a comparison of these with the corresponding characters in the albino rat. Jour. Comp. Neur., vol. 29.

author's abstract of this paper i«sued by the bibliographic service, february 16

METABOLIC ACTIVITY OF THE NERVOUS SYSTEM

II. THE PARTITION OF NON-PROTEIN NITROGEN IN THE BRAIN OF.

THE GRAY SNAPPER (nEOMAENIS GRISEUS) AND ALSO THE

BRAIN WEIGHT IN RELATION TO THE BODY

LENGTH OF THIS FISH

SHINKISHI HATAI

The Wistar Institute of Anatomy and Biology, and Department of Marine Biology, Carnegie Institution of Washington

ONE CHART

The prime object of the present investigation was to extend some observations made recently concerning the metabolic activity of the central nervous system of the albino rat (Hatai, '17) to the nervous system of lower vertebrates. It was my hope that such a comparative study might yield valuable data for an understanding of the complex phenomena of metabolism in this important organ.

In the course of the? present investigation I was able to accumulate a considerable amount of data on the weight of the brain together with its water content, a study which has revealed several interesting facts which have not been yet fully appreciated, so that I have decided to present these data also in the following pages. In connection with this work, it is a pleasure to acknowledge my indebtedness to Dr. A. G. Mayer, Director of the Department of Marine Biology of the Carnegie Institution of Washington. Dr. Mayer not only granted me the privileges of the laboratory at the Dry Tortugas, but gave me encouragement and many helpful suggestions throughout the cour&e of this work.

41

42 SHINKISHI HATAI

MATERIAL USED

The gray snapper, Neomaenis griseus, was chosen for this investigation not only because these fish are abundant in subtropical seas, but also because they possess numerous virtues for experimental purposes. The snapper may be kept in the laboratory for a long period, and in captivity as well as when free, takes almost any kind of food, cooked or raw, animal or .vegetable. The fish is well known for sagacity and boldness and is suited for various kinds of experimentation. Indeed the snapper has already been carefully studied by Reighard ('08) as to its behavior. Thus, with the hope that the gray snapper may in future prove to be a suitable form for certain lines of experimental work, I have utilized all the brains which have been used for chemical investigation, together with some others, for studying the growth of the brain in weight with respect to body length. Most of the fish were secured by netting them, but on account of the difficulty of getting the larger fish by this method, I have also used dynamite as well as the hook and line. I have noted in table 1 the method adopted for catching each individual.

TECHINQUE EMPLOYED

The fish w^ere examined as soon as they were brought into the laboratory. However, as in the case, of netting them, when too many were caught at once some were kept in a live box for not more than two days, except in a few cases in which they were kept for special purposes for several days. When the fish were kept in a live box for more than two days it is so stated in table 1.

In every instance the length of body was recorded in the following way. The fish was laid on its side and the length was determined by means of calipers from the tip of the snout to the middle of the caudal edge of the tail. The body weights of the fish were also taken in a few instances. Although I reahzed the desirability of recording the body weight in all cases, yet it was not always possible to make this measurement.

METABOLIC ACTIVITY OF NERVOUS SYSTEM

43

TABLE 1 Shoiving the brain weights according to various body lengths, together with the percentage of ivater in the brain, of the gray snapper. Arranged according to increasing body length

BODY

BRAIN WEIGHT

WATER IN

REMARKS

Length

Weight

BRAIN

7/1 m.

grams

grams

per cent

88

12

0.122

78.85

Net

137

43

0.234

78.63

Net

155

59

0.284

79.33

Net

215

0.622

79.52

Net

216

140

0.628

81.12

Dynamited

217

0.483

78.34

Net

225

0.670

79.05

Net

227

173

0.627

80.43

Dynamited

237

0.575

78.19

Net

• 238

197

0.660

79.91

Hook

240

0.711

79.92

Net

245

220

0.732

81.48

Dynamited

249

218

0.723

80.69

Dynamited

252

0.748

79.55

Net

252

0.762

78.64

Net

253

229

0.897

80.65

Dynamited

256

0.748

77.51

Net

258

0.828

79.47

Net

259

0.844

78.32

Net

262

0.833

78.75

Net

262

0.882

77.85

Net

263

0.864

77.29 9

Net

'263

269

0.803

80.08

Hook

263

261

0.816

79.68

Hook

268

0.859

79.74

Net

269

0.781*

77.49

Net

271

0.921

78.78 cf

Net

277

0.816

78.57

Net

278

0.843

78.32

Net

278

311

0.871

82.91

Hook

285

0.985

79.17 9

Net

293

1.006

77.28 d"

Net

294

0.861

78.86 d"

Net

295

0.925

77.56 d"

Dynamited

296

0.900

78.07

Net

298

0.982

78.49 d

Kept in live box

4 days

300

0.907

79.21 d

Dynamited

300

0.971

78.17 9

Net

301

0.952

77.10 o^

Net

44

SHINKISHI HATAI

TABLE

1 — Continued

BODY

BRAIN WEIGHT

WATER IN BRAIN

REMARKS

Length

Weight

mm.

grams

grajiis

per cent

302

1.042

77.87 9

Net

302

1.042

77.06 d"

Net

303

0.776

75.40 9

Dynamited

306

1.079

79.17 9

Kept in live box

317

0.974

78.03 d"

Net

318

1.072

79.57 9

Net

330

1.124

76.51 c?

Net

335

681

1.164

80.07 9

Kept several days in

box

336

1.124

77.67 9

Kept several days in

box

340

908

1.126

76.16 9

Net

345 ,

1.061

79.15 9

Net

348

iHbs.

1.141

77.46 9

Net

353

2 lbs.

1.117

76.63 9

Net

353

2 lbs.

1.169

77.81 9

Net

360

1.178

77.88 d

Net

362

1.257

78.65 d

Net

367

781

1.262

76.67 d

Hook

369

1.286

77.08 9

Net

374

2 lbs.

1.249

76.24 d

Net

380

3 lbs.

1.281

75.33 cf

Net

385

1.418

d"

Net

390

1.336

77.59 d

Net

392

1.353

79.67 d

Net

392

1.644

9

Dynamited

401

1.584

9

Dynamited

408

1.618

9

Dynamited

•

416

1.632

d^

Dynamited

424

1.369

78.54 9

Dynamited

430

1.400

' 9

Dynamited

432

1.424

79.97 d

Dynamited

438

1.530

d

Dynamited

439

1.400

9

Dynamited

439

1.499

83.00 9

Dynamited

441

1.601

9

Dynamited

448

1.591

9

Dynamited

As soon as the brain was exposed by means of a small bone forceps, it was separated from the spinal cord between the firstvertebra and the base of the skull. It was not practicable to find the first spinal nerve or to determine the caudal end of the fourth ventricle, methods which are usually adopted in separat

METABOLIC ACTIVITY OF NERVOUS SYSTEM

45

ing the brain from the spinal cord in the mammalian nervous system. Anteriorly the olfactory nerves were cut close to the olfactory bulbs. The saccus vasculosus was not included with the brain. The brain which was thus removed was placed in a small bottle which had been previously weighed, and this was weighed again to a milligram. After the fresh weight of the brain was determined, the bottle with its contents was placed in a steam oven at a temperature of 80°-90°C. for several days (Tortugas laboratory) and then later dried at the Wistar Institute under better laboratory conditions at 96°C. The various other methods used for the analysis of the brain will be described later.

THE BRAIN WEIGHT IN RELATION TO BODY LENGTH

Altogether observations on 74 brains of the gray snapper have been made.

From table 1 the average brain weight of the sanpper for several values of the body length has been calculated and the results are given in table 2.

In order to show the general distribution of the brain weights in relation to the body length, I have prepared a chart based on the data given in tables 1 and 2.

In the chart males and females are not distinguished. As will be seen from chart 1, the distribution of brain weight in respect

TABLE 2

Shoiving the average brain iveight of the gray snapper for the several values of the body

length

BRAIN

WEIGHT

BODY LENGTH

BODY LENGTH OBSERVED

NUMBER OF

HANGE

Observed

Calculated by formula

SNAPPERS

mm.

mm.

200-250

231

0.643

0.667

10

250-300

271

0.860

0.840

23

300-350

319

1.037

1.048

15

350-400

373

1.296

1.282

12

400-450

428

1.513

1.520

11

Average

1.070

1.071

46

SHINKISHI HATAI

to the increasing body length from 150 mm. upward is practically linear. This linear relation between these two characters is better shown by the positions of the averaged values, which are also plotted. It is well known that in the adult stage the relation between brain weight and body length or body weight is practically linear, even in the case of some mammals (see for instance growth of brain in weight in the albino rat in respect to body length or body weight, Donaldson, '09) but it is remarkable to find the linear relation in fish when they are so small. This linearity during the period of early growth probably means that in the gray snapper the brain reaches its struc

BRAIN WEIGHT

_j •

• ' -c-^^ u

1.5

. . •. _i-- t-_

^^^^ '

^^*

^i^L^

^-.i"^ '

1.0

^^^l5fL*

^^11 '

iT J^'l M n 1 1 1 1 1 1 M M 1 1 M 1 1

^v>

.5 "*

n 1 1 — 1 1 — 1 \ — 1 — 1 — ^ — ' — ' — 1 — 1 — ' — ' — ' — ' —

1 1 1 1 1 J 1 1 -L

50

100

150

200

250

.^00

350

400

450

Chart 1 Showing the weight of the brain of the gray snapper according to body length. The observed weights are represented by 74 fish. • = observed weight — o — o — = average observed weight (table 2).

tural maturity early, and that the subsequent increase in weight indicates merely a uniform swelling of the nervous system as a whole. The maturity of the brain at a relatively early stage of growth may be inferred also from practical constancy of the percentage of water in the brain from the very small to the very large fish in this series (page 48).

It is to be regretted that it was not possible to obtain data on smaller specimens, though every effort was made to obtain such specimens while I was at the Tortugas Laboratory. We were even unable to find any of the gray snapper fry, though the fry of the school master (Neomaenis apodus) which is most closely

METABOLIC ACTIVITY OF NERVOUS SYSTEM 47

related to the gray snapper, was abundant everywhere. Possibly the months of June and July were not a proper season to find them, or the fry of the gray snapper may not live in the open seas or along the beach, but may be in hiding under the intricate roots of mangroves, a tree not found on the Tortugas Islands.

On account of the scantiness of the data on the gray snapper less than 200 mm. in body length, I am unable to present a complete record of the growth of the brain. However it appears from the general trend of the growth curve that, with the possible exception of the very early period, the relation between the brain weight and body length does not deviate much from linearity.

Kellicott ('08) who studied the growth of the brain in the smooth dogfish (Mustelus canis, Mitchill) in respect to the body weight, found the graph to resemble that for the mammalian brain; that is the graph shows a rapid rise at the early period which is followed by a slower rate of growth. The form of the curve suggests a logarithmic formula such as was used to represent the growth of the brain in the albino rat (Hatai, '09). In other words the form of the graph for the gray snapper is strikingly different from that for the dogfish. This difference may be due to the fact that in the dogfish the brain possesses a voluminous cerebellum, as well as olfactory bulbs, and the combined weights of these two structures may be greater than that of the rest of the brain, while these two structures in the gray snapper are very small and the latter was not included. It appears that these two parts, olfactory bulbs and cerebellum, of the dogfish brain grow very rapidly during the earlier period, thus giving the form of the graph similar to that for the mammal.

Since the brain weight of the gray snapper shows a linear relation to the body length through a wide range, and since the fish which are usually caught fall within this range, I have devised the following formula for brain weight on body length, in hopes that it may prove useful for some future investigation.

Brain weight (gms.) = 0.00433 Body length (mm.) - 0.333.

The results of the calculation are given in table 2 and there

48 SHINKISHI HATAI

contrasted with the observed values. The agreement is highly satisfactory, and thus the formula may be employed when the probable brain weight of the gray snapper in which body length is known, is desired. I may point out that the absolute amount of increment of the weight of the brain following every millimeter increase of the body length is slightly over four milligrams (4,33 milligrams).

PERCENTAGE OF WATER IN THE BRAIN

Altogether 64 snappers were examined to determine the water content in the brain, and the results have been already given n table 1. An examination of the table reveals several striking relations in regard to the percentage of water. The percentage of water given by the smallest fish is 78.85 per cent while that of the larger fish, having a body length of 424 mm. and ranking in length third from the largest in which the water determination was made, gives 78.54 per cent. The frequency distribution of the percentage of water gives the following results.

TABLE 3

Showiny the frequency distribution of the percentage of water in the brain of the

gray snapper

PER CENT OF WATER

NUMBER OF CASES

75-76

2

76-77

5

77-78

15

78-79

17

79-80

16

80-81

6

81-82

2

82-83

1

Total number

64

Despite the fact of a wide range in the percentage o" water, the distribution of the frequencies is practically normal, and furthermore the high and low values are well mingled, when these

METABOLIC ACTIVITY OF NERVOUS SYSTEM 49

values are arranged according to the body length of the snapper (table 1) and there is no noticeable tendency for the lower values of the percentage of water to occur more frequently among larger fish, or vice versa. From this we infer that so far as the present data are concerned, the percentage of water in the small and large fish is nearly identical within a wide range of body length, and therefore the percentage of water does not vary regularly with the length or size of the fish. The average of 64 determinations gives the percentage of water as 78.61 per cent.

This wide variation in the percentage of water I am unable to explain at the present moment. It was thought at first that the method of capture, particularly the use of dynamite, might be responsible for it. Careful examination however (see remarks in table 1) of the table shows at once that such is not the case, and these wide variations are not correlated with the method of capture. It is true that the cranial cavity of the fish contains liquid as well as a jellylike substance, and the adhesion of particles of this substance may alter to some extent the percentage of water, but this factor is too insignificant to cause the wide variations shown in the table.

One other factor, though it appears to be important, cannot be readily tested, namely, masked age; that is a failure of the size and weight of the fish to indicate the age. We have no way to determine the age of the gray snapper. It may be that the size of the fish shows a wide range of variation for any given age. If size was positively correlated with age, then the low percentage of water would be given by the older fish, and vice versa. Therefore should we be able to arrange the data according to the ages of the fish, not the size of the fish as has been done, the values for the water should arrange themselves in a regular descending order with increasing age. This is, however, a mere speculation and must wait the test of future investigation.

Still another possible factor is the low grade of organization of the fish brain compared with that of the higher vertebrates. It is conceivable that owing to this low grade of organization, the structural maturity, or especially the process of myelination, may not progress regularly, and that within the same size or at

THE JOURNAX, OF COMPARATIVE NEUROLOGY, VOL. 29, NO, 1

50 SHINKISHI HATAI

the same age, a wide range of variation might exist in respect to the degree of myehnation, according to the environment of the fish or to the general nutritional conditions. Whether or not this suggestion has a value, only further investigation can determine.

Scott ('12) found that the percentage of water in the brain of the smooth dogfish differs very little between small and large specimens, and gives on the average 78.5 per cent. Donaldson ('05) who examined the brains of the summer flounder (Paralichthys dentatus) noted also but slight variation in the percentage of water in the brains of large and small individuals. The average from sixteen flounders in which the body weight ranges from 539 grams to 1290 grams, is 78.45 per cent. Thus the average percentages of water obtained by Donaldson, Scott and by myself are 78.45 per cent (flounder), 78.5 per cent (dogfish) and 78.61 per cent (gray snapper) respectively. For the purpose of comparison I gave the percentages of water in the brain of several fish, as determined by various investigators.

As will be seen from table 4 despite the widely different sizes and probably wide differences in the age of fish, the percentages of water in the brains are very close to one another, and further interest lies in the fact that the values given by the fish brains are not much different from the percentage of water in the adult mammalian brain.

Since the reduction in the water in the brain is induced by the deposition of the so called 'myelin substance' (Donaldson, '16) we may infer that the process of myelin ation in the fish brain attains its mature form at a very early period' thus permitting but very slight variation from small to large individuals. Scott ('12) also concludes from his observations on the water content

' In a private communication Dr. G. W. Bartelmez informs me that in Ameiurus melas, larvae 10 to 12 mm. long show already well advanced myelination of the roots of all the cranial nerves, as well as of the fasciculus longitudinalis medialis. The age of the larvae, according to Dr. Bartelmez 's estimate, is about ten to twelve days after fertilization. The largest adults measure as much as 120 mm. or nearly ten times the length of the larvae in which the myelination is already well advanced. From the above we may safely assume that myelination takes place in the fish at an early stage of development.

METABOLIC ACTIVITY OF NERVOUS SYSTEM

51

of the dogfish that the differences in the reduction of water in the two cases is that "the nervous (and body) changes which occur in the mammal are post-embryonic and extra-utero. In the

TABLE 4

Showing the percentage of ivater in thebrainsof several fish. Data compiled from

various sources

X

ALCO

SPECIES

BODY WEIGHT

o "

BRAIN WEIGHT

PER CENT OF WATER

HOLETHER

EXTRACT

SEX

OBSERVER

Cyprinus carpio

77.50

8.33

Von Bibra (1854)

Cyprinus barbus

78.00

9.37

Von Bibra (1854)

Salmo farco

78.92

8.42

Von Bibra (1854)

-80.00

Lucius esox

81.93

7.25 9.10

Von Bibra (1854)

Fish

Schlossberger

(1856)

Cyprinus auratus

77.80

Bezold (1857)

Summer flounder

539

393

0.253

78.05

Donaldson (1905)

Summer flounder

540

397

0.305

79.06

C^

Donaldson (1905)

Summer flounder

540

386

0.351

78.00

<f

Donaldson (1905)

Summer flounder

560

411

0.338

78.70

Donaldson (1905)

Summer flounder

630

409

0.279

78.06

&

Donaldson (1905)

Summer flounder

640

404

0.293

78.43

9

Donaldson (1905)

Summer flounder

682

405

0.288

79.56

Donaldson (1905)

Summer flounder

834

440

0.311

78.60

9

Donaldson (1905)

Summer flounder

840

462

0.358

78.98

9

Donaldson (1905)

Summer flounder

860

453

0.406

78.37

9

Donaldson (1905)

Summer flounder

880

459

0.381

77.11

cf

Donaldson (1905)

Summer flounder

890

459

0.417

77.98

9

Donaldson (1905)

Summer flounder

1010

460

0.355

78.22

9

Donaldson (1905)

Summer flounder

1010

447

0.369

78.72

cf

Donaldson (1905)

Summer flounder

1080

478

0.412

79.06

9

Donaldson (1905)

Summer flounder

1290

505

0.391

78.27

9

Donaldson (1905)

Average

78.45

Mustelus canis^

78.5

Scott (1912)

Barracuda

12 lbs.

1047

1.554

79.39 78.61

d'

Hatai (1917)

Neomaenis griseus^

Hatai (1917)

Cherna americana:

Red Grouper

14i lbs.

807

1.230

78.80

Hatai (1917)

Shark Sp?

160 lbs.

32.593

80.07

d"

Hatai (1917)

1 Average of 97 determinations from very small to very large. Percentage of water shows very slight variation.

2 Average of 51 gray snappers. Range of variation is shown in table (1).

52

SHINKISHI HATAI

dogfish they take place in utero." He, however, has not determined the water content in the brain of the dogfish in utero. From the foregoing it is clearly important to determine the water content in the brain of the fish at very early stages in order to discover the period of rapid reduction which must take place in consequence of the appearance of myelin in the brain. It is the hope of the writer to do this in the near future.

CHEMICAL ANALYSIS OF THE BRAIN (GRAY SNAPPER)

Utilizing the materials which were employed for the determination of the percentage of water, I have determined the nitrogen in the total solids, as well as the amount in the etheralcohol soluble fraction extracted from the total solids. The results of these determinations are shown in table 5.

TABLE 5

Showing the amount of the ether-alcohol soluble and insoluble fractions in the brain of the gray snapper; also the amount of nitrogen in the total solids, as well as the nitrogen in the ether alcohol fraction

BRAINS

WEIGHT OF

NITROGEN IN

SERIES

a

m

D Z

m K

SOLIDS

W.^TER

NITROGEN

Residue

Alcoholether Extract

Residue

Alcoholether Extract

weight

per cent

mgms.

gins.

gms.

mgms.

711 gms.

1

28

27.303

5.665

79.14

462

2.707

2.958

364

98

8.15%

47.79%

52.21%

78.79%

21.21%

2

19

20.013

4.588

77.07

334

1.938

2.650

269

65

7.28%

42.24%

57.75%

80.54%

19.46%

Ave

rage . .

78.11

7.72%

45.02%

54.98%

79.67%

20.33%

To carry out the determinations presented in table 5, I have divided the entire materials into two groups in which group 1 gives for the brain a percentage of water which ranges between 78 per cent and 80 per cent, while in group 2 the percentage of water ranges between 76 per cent and 77 per cent. All the other brains which gave percentages of water beyond these limits were excluded. Since all these data for the fish may be discussed conveniently by comparing them with similar data obtained

METABOLIC ACTIVITY OF NERVOUS SYSTEM 53;

from the rat brain, I may state simply that the values for the alcohol-ether soluble fraction obtained in this series of fish are similar to those obtained by Von Bibra ('54) and by Schlossberger ('56) in other forms of fish (table 3).

CONTENT OF 'NON-PROTEIN NITROGEN' IN THE BRAIN

Altogether 44 snappers of medium size were used for the purpose of determining the various extractive nitrogenous substances in the brain. These brains were divided into three samples, each giving nearly the same amount of moist brain weight. One additional sample was obtained from the brains of the schoolmaster (Neomaenis apodus) which is a species most closely related to the gray snapper.

The fresh brains of each sample were ground finely and then preserved in 150 cc. of 2.5 per cent solution of trichloracetic acid in water. - The ground brains were transferred to a bottle by means of 50 cc. water, thus making altogether 200 cc. of solution. The filtrates from this mixture were brought back to the Wistar Institute for analysis. The methods used for the determination of various nitrogen fractions were as follows:

1. Total non-protein nitrogen. Micro method of FoTin and Farmer as modified by Benedict and Bock.

2. Amino-acid nitrogen. Van Slyke's nitrous acid method. Also the same author's micro apparatus.

3. Urea nitrogen. Urease method.

4. Ammonia nitrogen. By the usual aerat on method.

In all cases, except the case of the amino acid, the nitrogen content was determined by means of the DuBoscq colorimeter. The results obtained from these determinations are given in table 6. i

Since it is my intention to discuss this subject later in comparison with the similar data recently obtained from the brain of the albino rat, I shall merely direct attention to the fact that these three samples give results very close to each other. - Furthermore the results obtained from the sample of the schoolmaster also agree with those found in the case of the gray snapper.

54

SHINKISHI HATAI

TABLE 6

Showing nitrogen content in terms of the 7io7i-proteins, the amino acids, the urea and the ammonia, in the brains of the gray snapper and of the 'schoolmaster.'

Number

Weight

MILLIGRAMS NITROGEN PER 100 GRAMS OF FRESH BRAIN

NonProtein

Anino acids

Urea

Ammonia

"Undetermined nitrogen

Neomaenis griseus

gms.

1

16

13.166

204

101.8

13.2

17.7

71.3

2

13

10.713

224

125.0

17.8

18.9

62.3

3

15

12.048

203

121.2

15.8

17.4

48.6

Average

11.976

210

116.0

15.6

18.0

60.7

Neomaenis apodus

10

11.195

225

126.0

17.3

17.2

64.5

This agreement in the various substances might also be taken to support the behef of the systematists that these two species are closely related.

COMPARISON BETWEEN THE GRAY SNAPPER AND THE ALBINO RAT IN REGARD TO THE CHEMICAL COMPOSITION OF THE BRAIN

In order to compare the data on the chemical composition of the brain in the gray snapper with those for the brain of the albino rat, table 7 was prepared. The entries for the fish are based on tables 5 and 6, while the data on the albino rat were obtained from an earlier paper (Hatai, '17).

When comparison is made between the fish brain and the entire brain of the albino rat, we find a distinct difference in regard to the content of the total nitrogen and of the nitrogen in the lipoids, as well as in the total amount of the ether-alcohol extractive materials. These differences must undoubtedly be correlated with anatomical differences 'n the two forms of the brains. In the rat we find a well developed cerebrum and cerebellum in which the myelinated nerve fibers are relatively less than in the stem, while the cell bodies are more abundant. On the other hand in these fish brains we find a mere trace of the

METABOLIC ACTIVITY OF NERVOUS SYSTEM

55

TABLE 7

Showing the comparison of the gray snapper with the albino rat in regard to the chemical composition of their brains

Water in brain, per cent

Total nitrogen in fresh tissue, per cent

Total nitrogen in solids, per cent

Alcohol-ether extract in solids, per cent

Nitrogen in alcohol-ether soluble fraction, per cent Percentage of water in lipoid-free tissue, per cent. . . Milligrams of non-protein nitrogen per 100 grams

of fresh tissue, milligrams '.

Partition of nitrogen in milligrams of nitrogen per

gram of solids

[Non-pro tein-N

JAmino-acids-N

|Urea-N

[Ammonia-N

Partition of non-protein nitrogen in percent of protein nitrogen I Non-proteins Amino acids Urea Ammonia

GR.^Y

ALBINO R.\T

SNAPPER

STEM OF

ENTIRE

ENCEPH.i

BRAIN

LON

78.11

75.16

1.69

1.89

7.72

7.75

54.98

55.03

20.60

19.90

88.80

87.06

225

150

9.6

6.0

5.3

2.9

0.7

0.7

0.8

0.6

13.04

9.72

7.20

4.68

0.97

1.05

1.11

1.04

ALBINO RAT ENTIRE BR.^IN

77.96 1.95 8.98 47-. 14 18.20 87.00

159

7.6 3.5 0.7 0.7

10.37 4.60 0.95 1.01

cerebrum and cerebellum compared with the size of the stem in which the myelinated nerve fibers are abundant. Consequently we should expect a higher value of the total nitrogen in the rat brain than in the fish brain, since the former possesses relatively a much greater number of cell bodies in those two well developed parts, the cerebrum and cerebellum. At the same time the rat brain ought to give relatively a less amount of hpoids, owing to tjhe great,er abundance of the gray matter in the predominant parts. In the fish brain the insignificant growth of the cerebrum and cerebellum makes the stem of the brain relatively predominant in the quantitative relations, and since the stem is the portion of the brain in which the myehnated fibers are mostly found, we should expect the percentage value of the lipoid fraction in the fish brain to be relatively higher than in the rat.

56 SHINKISHI HATAI

If we compare now the entire brain of the snapper with the stem of the albino rat brain (table 7) we notice a surprisinglyclose similarity. This we should expect since as was already stated the fish brain is practically represented by the stem, since the cerebral and cerebellar portions are relatively insignificant. Thus we notice the practical identity in the percentage values of the total nitrogen, hpoid nitrogen, and the amount of the Upoids. The percentage of water in the stem of the rat is however far less than in the entire brain of the fish which may be accounted for by the fact that in the brain of the fish the cerebrum and the cerebellum, though small ia relative quantity,* nevertheless are composed of structures rich in water, and thus bring the value of the water higher in the fish than in the stem alone of the albino rat brain.

The nitrogen content of the Upoid is sUghtly higher in the fish brain than in the albino rat brain, though almost identical with that in the stem. This difference may be due to the quantitative difference in the proportion of various lipoids in which the nitrogen content is not the same.

I now wish to consider the partition of the non-protein nitrogen in the fish brain compared with the brain of the albino rat. As will be seen from table 7 the content of the non-protein nitrogen is considerably greater in the fish than in the rat brain. We also notice that the greater part of the non-protein nitrogen is represented by the nitrogen of the amino acids. The nitrogen values given by both the urea and ammonia are small and are practically identical both in the fish and rat. The greater amount of non-protein nitrogen found in the fish brain in comparison to the rat is interesting, though I am unable to explain this difference satisfactorily. I wish however to call attention to two factors which may have some bearing on the difference just noted.

1. It seems probable that on account of the low grade of organization of the fish brain the physical consistence of the nervous system may not be as stable as that of the more highly organized mammalian nervous system, and thus the wear and tear process may be greater and produce a correspondingly greater amount of waste products in the fish brain.

METABOLIC ACTIVITY OF NERVOUS SYSTEM 57

2. According to Folin and Denis ('14) the normal human blood contains, on the average of four cases, 32 milligrams of nonprotein nitrogen per 100 cc. of blood, while Wilson and Adolph ('17) found in the blood of various fresh water fish much higher values for the non-protein nitrogen (42 mgms. per 100 cc.) than in the human blood, and furthermore these investigators found a greater fraction of the non-protein nitrogen was represented by the nitrogen of amino acids (23 mgms. per 100 cc. or about 55 per cent of the total non-protein nitrogen). Thus my own observations on the fish brain closely agree with those of Wilson and Adolph on the fish blood, so far as the relative abundance of the non-protein nitrogen is concerned, as well as in the relation of the amino acid nitrogen to the total non-protein nitrogen.

Denis ('13-' 14) found also a considerably greater amount of non-protein nitrogen in the blood of marine fishes when contrasted with human blood. Denis found 62 mgms. of non-protein nitrogen per 100 cc. of blood (average of 10 species of teleosts) and as high as 1087 mgms. in the case of the elasmobranchs (average of three species). Thus the greater abundance of the non-protein nitrogen in the fish blood, accompanied by a slow circulation, might be largely responsible for a greater accumulation of the non-protein nitrogenous extractive substances in the fish brain.

SUMMARY

The gray snapper, Neomaenis griseus, was mainly used for the present investigation. The following are the more important facts brought out.

1. The relation between brain weight and body length is practically linear. This linear relation appears in the fish as small as 150 mm. in length. The fish smaller than 150 mm. were not studied because they could not be obtained.

2. The percentage of water in the brain varies very little from small to large (body length : 88 mm. to 448 mm.). A similar relation was observed by Donaldson ('05) in the brain of the summer flounder and by Scott ('12) in the brain of the smooth dogfish. The probable explanation is that the process of mye

58 SHINKISHI HATAI

lination is completed in the fish brain relatively earlier than in the mammalian brain.

3. With respect to the total nitrogen, nitrogen in ether-alcohol extract, and the lipoid content, the fish brain closely resembles the stem of the rat brain, but significantly differs from the entire rat brain. This is explained by the fact that the mature fish brain resembles essentially the stem of the mammalian brain owing to the small growth of cerebrum and cerebellum.

4. The non-protein nitrogen is considerably greater (42 per cent) in amount in the fish brain than in the rat brain. The suggestions were made that probably on account of unstable physical consistence of the fish nervous system, the wear and tear of the neurons may be greater than in the more highly organized mammalian nervous system, thus producing a larger quantity of the waste products, and also that on account of higher nonprotein nitrogen content of the fish blood, accompanied by a slow circulation, the deposition of the waste products might become greater, and at the same time a less vigorous removal further tends to increase the accumulation.

5. The greater fraction of the non-protein nitrogen is represented by the amino acid nitrogen in both the fish and the rat.

6. The amounts of urea nitrogen and of ammonia nitrogen are closely similar to those found in the rat braiuc

METABOLIC ACTIVITY OF NERVOUS SYSTEM 59

LITERATURE CITED

Be?old, a. von 1857 Untersuchungen liber die Vertheilung von Wasser, organisdher Materie und anorganischen Verbindungen im Thierreiche. Zeitschr. f. wiss. ZooL, vol. 8.

BiBRA, Ernest von 1854 Vergleichende Untersuchungen tiber das Gehirn des Menschen und der Wirbelthiere. Verlag von Basserman u. Mathy. Mannheim.

Denis, W. 1913-1914 Metabolism studies on cold-blooded animals. 2, The blood and urine of fish. J. Biol. Chem., vol. 16, pp. 389-393.

Donaldson, H. H. 1905 On the percentage of water in the brain of the summer flounder, according to body weight. Not published — in manuscript. 1909 On the relation of the body length to the body weight and to the weight of the brain and of the spinal cord in the albino rat (Mus norvegicus var. albus). Jour. Comp. Neur., vol. 19, pp. 155-167.

1915 The Rat. Reference tables and data for the albino rat (Mus norvegicus albinus) and the Norway rat (Mus norvegicus). Memoirs of the Wistar Institute of Anatomy and Biology, no. 6.

1916 A preliminary determination of the part played by myelin in reducing the water content of the mammalian nervous system (albino rat). Jour. Comp. Neur., vol. 26, pp. 443-451.

FoLiN, Otto and Denis, W. 1914 On the creatinine and creatine content of

blood. Jour. Biol. Chem., vol. 17, pp. 487-491. Hatai, S. 1909 Note on the formulas used for calculating the weight of the

brain in the albino rats. Jour. Comp. Neur., vol. 19, pp. 169-173.

1917 Metabolic activity of the nervous system. I. Amount of nonprotein nitrogen in the central nervous system of the normal albino rat. Jour. Comp. Neur., vol. 28, pp. 361-378.

Kellicott, W. E. 1908 The growth of the brain and viscera in the smooth

dogfish (Mustelus canis, Mitchill). Am. Jour. Anat., vol. 8, pp.

319-353. Reighard, J. 1908 An experimental field study of warning coloration in coral

reef fishes. Papers from the Tortugas Laboratory, Carnegie Inst.

Washington, vol. 2. Schlossberger, J. E. 1856 Allegemeinen und vergleichenden Thierchemie.

Leipzig u. Heidelberg. Scott, G. G. 1912 The percentage of water in the brain of the dogfish. Proc.

Soc. Exp. Biol, and Med., vol. 9, no. 3. Wilson, D. W. and Adolph, E. F. 1917 The partition of non-protein nitrogen

in the blood of fresh water fish. Jour. Biol. Chem., vol. 29, pp. 405 41L

author's abstract of this paper issued

BY the bibliographic SERVICE, FEBRUARY 2

COMPARATIVE STUDIES ON THE GROWTH OF THE CEREBRAL CORTEX

V. PART I. ON THE AREA OF THE CORTEX AND ON THE NUMBER OF CELLS IN A UNIT VOLUME, MEASURED ON THE FRONTAL AND SAGITTAL SECTIONS OF THE ALBINO RAT BRAIN, TOGETHER WITH THE CHANGES IN THESE CHARACTERS ACCORDING TO THE GROWTH OF THE BRAIN

V. PART II. ON THE AREA OF THE CORTEX AND ON THE NUMBER OF CELLS IN A UNIT VOLUME, MEASURED ON THE FRONTAL AND SAGITTAL SECTIONS OF THE BRAIN OF THE NORWAY RAT (mUS NORVEGICUS), compared WITH THE CORRESPONDING DATA FOR THE ALBINO RAT

NAOKI SUGITA From the Wistar Institute of Anatomy and Biologij

THREE FIGURES AND FOUR CHARTS

PART I

I. INTRODUCTION

The present study is an extension of an earlier one on the thickness of the cerebral cortex in the albino rat (Sugita, '17 a) and aims to present the extent of the actual area occupied by the cortical cells, as seen in sections which were taken from the fixed levels of the albino brain, and also to follow the changes in this area during the postnatal growth of the brain. In the course of this investigation, the number of nerve cells contained in a unit volume of a fixed locahty in the frontal i section was counted and the changes in this number with advancing age were ascertained. Furthermore the relation between the cell number and the cortical area was critically examined.

For this study, the sections, which had been previously used for the investigation of the thickness of the cortex of the albino rat brain, were again utilized. The material, amounting to 78

61

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 2 APRIL, 1918

62 NAOKI SUGITA

albino rats, sexes combined, which was used in the present study, is identical with that listed in table 1 of the former paper (Sugita, '17 a), to which the reference should be made for this studyalso.

These studies were made during the winter semester of 19161917.

II. MEASUREMENTS AND ENUMERATIONS

A. Area of the cortex in the sagittal section

As previously described (Sugita, '17 a), the sagittal section (fig. 1) was taken in a plane passmg through the frontal pole afid parallel to the mesial surface of the hemisphere. This section from each individual brain was projected on a sheet of paper by the Leitz-Edinger Projection apparatus, at a magnification of exactly twenty diameters, and the outline of the image then accurately traced on the sheet. At the transitional part of the cortex at the frontal pole to the olfactory bulb and at the subiculum, where the cortex goes over into the structure of the cornu Ammonis, the borderlines were drawn along the radiation of the cells in those parts (fig. 1). The anterior borderline (a-a') is formed by a prolongation of the line bounding the dorsal surface of the olfactory bulb. The posterior borderline (p-p') is clearly located, because this was drawn at the point where the thickness of the ganglionic layer abruptly diminishes at the beginning of the ganglion cell band characteristic for the cornu Ammonis. The area of the cortex, including the lamina zonalis, which contains no proper nerve cells, was then repeatedly measured to a square millimeter on the drawing, using the Ott Compensating Planimeter. The values obtained were then averaged, and 1/400 of the value, which corresponds to the cortical area on the slide, was recorded. This value was then converted into that for the fresh condition of the material, by the following procedure.

On the outline, which was taken from the section on the slide, the diameter from frontal pole to the occipital pole (L. F) was measured and reduced, and, according to the formula given in the former paper (Sugita, '17 a), which reads

GROWTH OF THE CEREBRAL CORTEX

63

Correction-coefficient =

The diameter L. F in fresh cerebrum

The diameter L. F on the shde the correction-coefficient was determined. The value for the area obtained by the (first) direct measurement from the slide was then corrected to the corresponding value for the fresh condition of the material, by multiplying by the square of the correction-coefficient. The corrected values thus obtained are given in the last column of table 1.

The values for the cortical areas in the respective sagittal sections of each individual were then grouped according to the

Fig. 1 Showing, by shading, the cortical area measured on the sagittal section of the albino rat brain. The anterior borderline ((a-a') is formed by a prolongation of the line bounding the dorsal surface of the olfactory bulb. The posterior borderline {p-p') is drawn at the point where the ganglionic layer goes over abruptly to the ganglion cell band in the cornu Ammonis.

brain weight, into twenty groups, as in the other studies of this series, and the average value for each group was found. The average areas of the cortex in the sagittal section for each group (table 1) were plotted in chart 1 (graph s), which shows the increase in area according to the increase in brain weight.

B. Area of the cortex in the frontal section

The frontal section (fig. 2) was cut in the plane passing through approximately the middle point of the mesial surface of the

64

NAOKI SUGITA

TABLE 1

Shoiving the observed and corrected values of the area of the cerebral cortex in the sagittal section of the albino rat brain, accompanied by the data for the correctioncoefficient in the individual cases and the correction-coefficient for the group. L. F is the longitudinal diameter of the cerebrum

BRAIX WEIGHT

OBSERVED

AREA OF CORTEX

CORRECTION-COEFFICIENT

CORRECTED

GROUP

L. F in fresh brain

The same on slide

AREA OF CORTEX

grams

mm.

mm.

mm.

mm."^

la

0.153

3.2

5.50

4.97

4.1

c

0.154

3.0

5.60

4.80

4.1

b

0.177

4.0

5.70

5.13

4.9

0.161

5.4

1.

13^

4.4

II a

0.213

4.0

5.80

5.13

5.1

b

0.221

3.9

6.00

5.43

4.8

c

0.261

4.8

6.60

5.60

6.7

d

0.271

4.8

6.75

5.80

6.5

e

0.288

4.5

6.70

5.75

6.1

■ (Birth)

0.251

4.4

1.

15-^

5.8

III a

0.311

6.1

7.35

6.45

7.9

1)

0.322

6.3

7.20

6.40

8.0

g

0.374

8.1

7.40

7.40

8.1

c

0.390

6.7

7.50

6.70

8.4

i

0.395

7.4

7.95

7.20

9.0

0.S58

6.9

1.

10^

8.3

IV b

0.400

6.7

7.70

6.65

9.0

a

0.402

8.4

7.75

7.30

9.4

e

0.420

8.2

7.95

7.20

10.0

i

0.443

10.6

8.30

8.10

11.1

d

0.459

8.8 •

8.05

7.60

9.9

e

0.466

9.6

8.40

7.80

11.1

0.^32

8.6

/.

082

10.1

Vi

0.501

10.2

8.35

7.90

11.4

a

0.525

12.7

8.55

8.45

12.9

b

0.528

11.1

8.50

8.05

12.4

c

0.534

9.0

8.65

7.60

11.6

d

0.537

10.1

8.30

7.70

11.7

e

0.555

12.3

9.25

8.65

14.0

f

0.558

11.0

9.20

8.50

12.9

g

0.564

11.4

8.85

8.40

12.7

h

0.579

11.5

9.10

8.35

13.6

0.542

11.0

1.07'^

12.6

GROWTH OF THE CEREBRAL CORTEX

65

TABLE 1— Continued

BRAIN WEIGHT

OBSERVED

ARE.\ OF CORTEX

CORRECTION-COEFFICIENT

CORRECTED

GROUP

L. F in fresh brain

Th

e same on slide

AREA OF CORTEX

(/rams

mm."

m m .

??i m .

?« m .2

VI c

0.610

12.0

9.35

8.35

14.9

a

0.617

10.7

9.25

7.95

14.4

e

0.090

15.0

9.60

9.00

17.1

0.639

12.6

1.

ir

15.5

VII a

0.740

15.7

10.50

9.80

18.1

b

0.760

11.5

10.65

8.50

18.1

0.750

13.6

1.15-'

18.1

VIII a

0.800

14.4

10.50

9.25

18.5

h

0.805

13.8

10.90

9.20

19.4

b

0.822

16.2

10.45

9.60

19.2

c

0.849

18.0

10.50

9.70

21.1

k

0.870

15.1

10.95

9.40

20.5

d

0.898

17.0

11.45

10.15

21.6

0.841

15. S

1.13^ 1

20.1

IX d

0.959

17.9

11.60

10.50

21.8

e

0.960

16.9

11.40

9.85

22.5

a

0.972

15.4

11.30

9.70

20.9

(10 days)

0.964

16.7

/.

W

21.7

X a

1.033

13.9

11.90

9.40

22.3

b

1.036

15.9

11.85

9.85

23.1

e

1.051

17.5

12.05

10.05

25.0

1.040

15.8

1.

22"

23.5

XI a

1.107

17.3

12.00

10.00

25.2

b

1.189

18.8

12.50

10.25

28.0

c

1 . 193

19.1

12.65

10.50

27.8

d

1.195

16.0

12.60

10.00

25.4

(20 days)

1.171

17.8

1.22' 1

26.6

'XII c

1.234

18.4

12.30

10.35

26.0

a

1.273

15.7

12.45

9.65

26.2

1.253

17.1

1.

2J,'

26.1

XIII a

1.301

18.7

13.00

11.10

25.7

g

1.307

15.6

12.95

10.00

26.2

b

1.327

17.2

13.20

10.50

27.2

c

1.346

17.8

13.00

10.10

29.5

h

1.392

21.9

13.45

11.60

29.5

1.335

18.2

1.2S'

27.6

66

naoki sugita

TABLE \— Concluded

BRAIN WEIGHT

OBSERVED AREA CORTEX

CO RRECTION-COEFFICIENT

CORRECTED

GROUP

L. F in fresh brain

The same on slide

AREA OF CORTEX

grams.

mm.

mm.

mm.

mm. 2

XIV a

1.412

17.5

13.40

10.40

29.1

e

1.441

15.2

13.25

10.10

26.2

b

1.483

21.1

13.30

11.30

29.3

1.U5

17.9

1.

26^

28.2 ■

XV a

1.530

17.4

13.70

10.80

28.1

b

1.542

19.6

13.50

11.40

27.5

c

1.552

17.2

13.70

10.65

28.6

d

1.573

20.0

13.70

11.15

30.1

e

1.574

18.9

13.75

11.05

29.3

1.554

18.6

l.£

4'

28.7

XVI a

1.642

18.9

14.10

11.30

29.4

g

1.643

18.7

14.65

11.60

29.7

c

1.647

18.7

13.75

11.05

29.0

e

1.690

17.5

13.65

10.70

28.6

1.656

18.4

1.

26^

29.2

XVII f

1.720

18.3

14.90

11.60

30.2

a

1.721

18.4

13.90

10.90

29.8

b

1.730

23.5

13.85

11.70

32.8

c

1.731

20.8

14.30

11.60

31.7

1.726

20.2

1.

u^

31.1

XVIII c

1.817

18.5

15.20

11.50

32.4

a

1.844

24.7

14.00

12.10

33.0

e

1.855

21.6

15.05

12.15

33.1

1.839

21.6

1.

24^

32.8

XIX a

1.924

20.6

15.40

12.30

32.3

i.m

20.6

1.

25^

32.3

XX a

2.039

22.6

15.10

12.60

32.5

b

2.069

25.1

15.55

13.20

34.8

2.054

23.9

1.19'

33.7

hemisphere and cutting the corpus callosum, the conunissura anterior and the chiasma opticum (Sugita, '17 a). On the drawing of the outhne of the frontal section (fig. 2), which was traced

GROWTH OF THE CEREBRAL CORTEX

67

in the same manner as that for the sagittal section, the dorsal and the ventral borderlines of the cortical are^ were drawn. The dorsal border (d) was determined by the ectal borderline of the corpus callosum, which lies under the tip of the cortex at the bottom of the fissura sagittalis, and the ventral border {v-v') was drawn perpendicular to the surface at the basal end of the cell group which is found under the cortex proper just below the region of the fissura rhinalis, latero-basal to the cap

Fig. 2 Showing, by shading, the cortical area measured on the frontal section of the albino rat brain. The dorsal border (d) is chosen at the borderline of the corpus callosum. The ventral border (v-v') was drawn perpendicular to the surface at the basal end of the cell group found near the fissura rhinalis, latero-basal to the capsula externa. The double shaded part, locality VII, indicates the area where the cell number and cell size were determined.

sula externa. This latter border is not so sharply defined, but we could not find any better marking point than this cell group. The area of the cortex, thus bounded, was then measured and recorded. In making the measurement, the area of the cortex was at first measured and then the total area of the frontal section, — of one hemicerebrum — excluding the cavity of the lateral ventricle and the tractus opticus, was measured. The ratio of the cortical area to the total area of the section was then computed. Correction of the observed values to those for the

68

NAOKI SUGITA

fresh condition of the material was made in the same manner as for the sagittal cortex, by multiplying by the square of the value of the correction-coefficient. This latter was obtained by the formula given in a former paper (Sugita, '17 a), as follows:

The diameter W. D in fresh cerebrum

Correction-coefficient =

The diameter W. D on the slide

li 70 (,5 60 55 50 45 40 35 30 25 20 15 10 5

..-T

/

/'

^

'

~y

-;>-'

>

i^

^^

^'

v

i

'

1

t

i

■■/^

^,.--'

i 1 !

^

-^j

.--'

-'—

---^

! i

,y.

y

^.^

^^

s

/f

^'^

^

■^

/

i

^

■>^

i

^

^

'^

1 ■

s=

j i

\ 1

'O 0.1 Q2 0.3 Q4 Q5 06 07 Q8 Q9 10 11 12 13 14 15 16 IT 18 19 2.0 ^s.

Chart 1 Showing the corrected areas of the cerebral cortex in the sagittal

and the frontal sections and the area of the whole frontal section, all according

to the brain weight, accompanied by the theoretical value of the last which is

assumed to be proportional to the square of the cube root of the brain weight.

Albino rat. X— • — ■ — • X, Cortical area in the sagittal section, o oof

Cortical area in the frontal section. • 'F, Area of the whole frontal section.

T, Theoretical area of the frontal section, i.e., the square of the

cube root of the brain weight. All graphs are based on the data in tables 1 and 2.

These data are all entered in table 2, in which the average measurements for each brain weight group are also given. The graphs for the total area of the frontal section (graph F) and for the area of the frontal cortex (graph f) in chart 1 are based on the corrected data given in table 2.

TABLE 2

Showing the observed and corrected values of the area of the cerebral cortex and of the total frontal section and the percentage of the cortical area to the total frontal section of the albino rat brain, accompanied by the data for the correction-coefficient in the individual cases and the correction-coefficient for the group. W. D is the frontal diameter of the cerebrum

OBSERVED

CORRECTIONCOEFFICIENT

CORRECTED

PERCENTAGE OF

BRAIN WEIGHT

CORTICAL

GROUP

Area of cortex

Area of

total section

W. D

in fresh brain

The same on slide

Area of cortex

Area of

total section

AREA IN

TOTAL

c SECTION

grams

mm. 2

mTO.2

mm .

m m .

»i m .2

vim.^

per cent

la

0.153

2.8

9.2

6.45

5.65

3.7

12.0

34

c

0.154

2.6

8.2

6.35

5.40

3.6

11.4

34

b

0.177

3.5

9.9

6.95

6.26

4.3

12.2

35

0.161

3.0

9.1

1.

W

3.9

11.9

35

II a

0.213

4.4

13.0

8.40

7.35

5.7

17.0

34

b

0.221

3.6

11.9

7.95

6.50

5.4

17.8

30

c

0.261

4.6

13.0

7.80

7.10

5.6

15.7

36

d

0.271

4.4.

13.1

7.75

6.80

5.7

16.9

34

e

0.288

4.1

11.8

8.55

7.05

6.0

17.4

35

(Birthj

0.251

4.2

12.6

1.

16"

5.7

17.0

34

III a

0.311

5.1

15.3

8.50

7.65

6.3

18.9

33

b

0.322

5.1

13.0

8.70

6.80

8.3

21 .2

39

g

0.374

7.2

19.0

8.95

8.40

8.2

21.6

38

c

0.390

6.5

15.9

8.85

7.60

8.8

21.5

39

i

0.395

7.5

17.8

9.10

8.60

8.4

20.0

42

0.358

6.3

16.2

1.13^

8.0

20.6

39

IV b

0.400

7.6

19.4

9.00

8.50

8.5

21.7

39

a

0.402

6.8

16.7

9.10

7.90

9.0

22.2

41

c

0.420

6.7

17.9

9.00

8.15

8.2

21. g

38

i

0.443

8.0

19.0

9.15

8.40

9.4

22.3

42

cl

0.459

6.9

17.2

9.50

7.95

9.8

24.5

40

e

0.466

9.4

21.8

9.30

9.25

9.5

22.1

43

o.m

7.6

18.7

l.W

9.1

22.4

41

Vi

0.501

9.0

22.3

9.80

9.20

10.2

25.3

40

a

0.525

9.8

22.4

9.65

9.10

11.0

25.2

44

b

0.528

8.7

19.6

9.90

8.60

11.5

26.0

44

c

0.534

7.6

18.6

10.30

8.25

11.4

29.0

39

d

0.537

8.8

20.1

10.00

8.80

11.4

26.0

44

e

0.555

9.9

22.5

9.90

9.00

12.0

27.2

44

f

0.558

9.2

20.0

10.00

8.55

12.6

27.4

46

g

0.564

10.2

22.9

10.10

9.15

12.4

28.0

44

h

0.579

10.1

22.1

10.10

9.05

12.8

27.6

46

0.542

9.3

21.2

1.13

11.7

26.9

u

69

TABLE 2~Continued

OBSERVED

CORRECTIONCOEFriCIENT

CORRECTED

PERCENTAGE OP

BRAIN WEIGHT

CORTICAL

GROUP

Area of cortex

Area of

total

section

W. D

in fresh brain

The same on slide

Area of cortex

Area of

total section

AREA IN

TOTAL SECTION

grams

WOT .2

invi.^

mm.

7)1 m.

TOOT.2

mm.

per cent

Vie

0.610

9.9

21.7

10.15

8.50

14.1

31.0

46

a

0.617

9.6

21.6

10.55

8.65

14.3

32.2

44

e

0.690

11.6

23.7

10.60

9.40

14.8

30.2

49

N

0.639

10.4

22.3

1.

19'

14.4

31.1

46

Vila

0.740

11.1

22.1

11.00

9.20

15.9

31.6

50

b

0.760

10.2

20.3

11.20

8.70

16.9

33.6

50

0.750

10.7

21.2

1.,

24'

16. 4

32.6

50

Villa

0.800

10.6

21.8

11.15

8.60

18.8

36.7

51

h

0.805

11.3

23.6

10.60

8.30

18.5

38.6

48

b

0.822

13.6

28.5

11.85

10.20

18.4

38.5

48

c

0.849

13.7

28.8

11.40

9.90

18.2

38.3

48

k

0.870

13.4

27.7

11.45

9.60

19.1

39.5

48

d

0.898

13.1

31.2

11.75

10.20

17.4

41.5

42

0.841

12.6

26.9

1.

202

18. 4

38.9

48

IX d

0.959

13.5

28.4

11.80

9.70

20.0

42.0

48

e

0.960

13.8

29.4

12.15

10.10

20.0

42.6

47

a

0.972

14.3

28.4

11.95

9.80

21.3

42.4

50

(10 days)

0.964

13.9

28.7

1.

2P

20.4

42. 3

48

Xa

1.033

14.1

30.3

12.40

10.30

20.4

44.0

46

b

1.036

13.4

30.5

12.40

10.15

20.0

45.5

44

e

1.051

13.2

25.9

12.10

9.40

21.8

43.0

51

1.040

13.6

28.9

1.

23'

20.7

44.2

47

XI a

1.107

13.7

28.7

12.90

10.20

21.8

45.7

48

b

1.189

13.3

27.8

13.15

10.30

21.7

45.4 '

48

c

1 . 193

14.6

30.8

12.70

10.30

22.2

47.0

47

d

1.195

12.8

27.2

12.50

9.80

21.0

44.5

47

(20 days)

1.171

13.6

28.6

1.

26^

21.7

45.7

48

XII c

1.234

15.0

31.9

12.95

10.70

22.0

46.8

47

a

1.273

11.9

23.6

12.90

9.10

24.0

47.5

50

1.25S

13.5

27.8

1.

3r

23.0

47.2

49

XIII a

1.301

13.9

28.3

13.20

10.25

23.0

47.1

49

g

1.307

13.9

29.9

12.70

10.00

22.5

48.3

47

b

1.327

12.2

28.2

13.35

9.70

23.2

53.3

43

c

1.346

13.3

29.0

13.15

9.85

23.7

51.8

46

h

1.392

16.3

34.8

13.10

10.90

23.6

50.3

47

1.335

13.9

30.0

1.29^

23.2

50.2

46

70

TABLE 2—Co7icluded

OBSERVED

CORRECTIONCOEFFICIENT

CORRECTED

PERCENTAGE OF

BHAIN WEIGHT

CORTICAL

GROUP

Area of cortex

Area of

total

section

W. D.

in fresh brain

The same on slide

Area of corte.x

Area of

total section

AREA IN

TOTAL SECTION

grams

mm. 2

m m .

171 m.

mm.

»»m.2

mm. 2

■per cent

XIV a

1.412

13.9

29.4

13.65

10.30

24.4

51.6

47

e

1.441

12.4

25.7

13.10

9.20

25.2

51.0

49

b

1.483

15.2

33.3

13.80

10.80

24.8

54.4

46

1445

13.8

29.5

1.34""

24.8

52.3

47

XV a

1.530

14.4

33.6

13.80

10.80

23.5

54.8

43

b

1.542

13.9

30.5

13.70

10.40

24.2

53.0

46

c

1.552

14.2

31.7

13.50

10.30

24.4

54.4

45

d

1.573

14.2

30.8

13.90

10.60

24.4

53.1

46

e

1.574

14.8

32.2

13.70

10.50

25.2

54.8

46

1.554

14-3

31.8

l.l

?02

24-3

54.0

45

XVI a

1.642

16.4

37.0

13.80

11.20

24.9

56.2

44

g

1.643

11.6

27.4

13.40

9.50

23.2

54.7

42

c

1.647

14.3

29.8

14.00

10.50

25.5

53.2

48

e

1.690

13.0

30.7

13.45

10.00

23.5

55.3

42

1.656

13.8

31.2

l.t

J32

24.3

54.9

44

XVII f

1.720

12.5

28.7

13.50

9.60

24.8

56.8

44

a

1.721

14.8

34.5

14.00

11.00

24.0

56.0

43

b

1.730

17.5

40.4

14.70

12.35

24.8

57.2

43

c

1.731

17.5

39.2

14.40

12.10

24.8

55.6

45

1.726

15.6

35.7

l.i

W

24.6

56.4

44

XVIII c

1.817

13.3

31.1

14.00

10.10

25.6

59.8

43

a

1.844 1.855

17.4

38.1

15.00

12.10

26.7

58.5

46

e

14.2

32.0

14.30

10.60

25.8

58.3

44

1.839

15.0

33.7

l.t

?^2

26.0

58.9

44

XIX a

1.924

14.8

33.9

14.10

10.90

24.8

57.0

44

1.924

U.8

33.9

l.i

w

2^.8

57.0

44

XX a

2.039

16.8

42.7

■ 14.80

12.10

25.2

63.9

39

b

2.069

15.7

40.3

14.60

11.70

24.5

62.8

39

2.054

16.3

41.5

1.23'

24-9

63.4

39

C. Number of nerve cells

On the frontal sections used for the measurement of the cortical area, the number of nerve cells contained in a unit volume at a fixed locality in the cortex was counted. The locality selected was at the middle part of the cortical band (fig. 2, VII), designated as locality VII in figure 4 in a former paper (Sugita,

71

72 NAOKI SUGITA

'17 a). To represent the cortex, the lamina pyramidaHs and the lamina ganglionaris were selected. By the use of the ocular net-micrometer (with Zeiss Comp. Ocular 6 and Zeiss objectives 2 mm. and 4 mm.), the number of nerve cells in five adjoining squares along the cortical band, each square 100 micra on a side, was counted in a given location. The numbers obtained were added together and then, by multiplying by two, was converted to the number in a unit area of 0.1 mm.- on the section. This value, the number of nerve cells in a slice of cortex, 0.1 mm." in area and 10 micra thick (the thickness of the section) or 0.001 mm.^ in volume, was then reduced to the number in this volume in the fresh condition of the brain. To make this reduction, I used as the correction-coefficient the cube of the reciprocal of the correction-coefficient obtained by the for The diameter W. D in fresh cerebrum , . , , , ,

mula: =- v-. -— — 7r\ ' which had been

1 he diameter W . D on the slide

previously employed, because the section on the slide was assumed to have shrunken in all three dimensions equally at the rate of the correction-coefficient and therefore a unit volume in the fresh condition would correspond to the volume of the unit on the slide multiplied by the cube of the reciprocal of the correction-coefficient.

In the lamina pyramidalis, the pyramids are more densely crowded at the ectal than at the ental part of the lay?r, which adjoins the lamina granulans interna. I adjusted the upper line of the net-micrometer squarely on the border between the lamina zonalis and the lamina pyramidalis and counted the cell number included in a square, 100 micra on each side, at the ectal part of the layer, where the cells are crowded densely. If large blood vessels appeared in the microscopic field, I gave up such a field and counted an adjoining one where no large vessels were present.

In the lamina ganglionaris the large ganglion cells are mixed with a number of small pyramids, almost equal in size to, or somewhat smaller than, the pyramids in the lamina pyramidalis. At first, the number of all the nerve cells, the large and small combined, was counted. Then the large ganglion cells, which

GROWTH OF THE CEREBRAL CORTEX 73

surely represent a group distinct from the small pyramids, were counted alone. So, by subtraction, the number of small pyramids only in the lamina ganglionaris was obtained. In counting the ganglion cells, I adjusted the lower line on the net-micrometer accurately on the border between the lamina ganglionaris and the lamina multiformis, because between the lamina ganglionaris and the lamina granulans interna there is found a pale band poor in cells and therefore it was not convenient to adjust the upper line of the net-micrometer at this border. The number of cells observed, in a slice of 0.1 mm.'- in area and 10 micra thick on the slide, were in the similar manner recorded and by the use of the same correction-coefficients, as were used in the case of the pyramidal cells, were reduced to the number for the fresh condition of the brain.

Out of the total number of cells, which came in view in the microscopic field, about one-third does not contain the nucleoli in the cell nuclei. This means that the nucleoli in question lie outside of the section. Nevertheless I counted the cells having nuclei without nucleoli together with those in which nucleoli were to be seen, because my object was to ascertain the cell density in the locality chosen and not to determine the total number of nerve cells in a series of sections. In the latter case, the double counting of one and the same cell must be necessarily avoided. On the other hand, the cells which were represented in the section by only fractions of the cell bodies without nuclei were omitted from the counting. The number of such cells was small. Neuroglia nuclei, which were to be easily distinguished by their smaller size, and the intima cells of the capillaries, if they came in view, were not counted.

Table 3 shows the results of these enumerations.

III. DISCUSSION

D. The area of the cortex in the sagittal section

Examinmg table 1 and chart 1 (graph s), which give the area of the cortex in the sagittal sections of the albino rat brain, it is seen that the area increases steadily with increasing brain weight.

TABLE 3

Giving for each individual and for each brain weight group the number of nerve cells in 0.001 vim.^ in volume of the cortex, in the lamina pyramidalis and in the lamina ganglio7iaris, and also the mimber of the ganglion cells in the lamina ganglionaris, all counted at the middle part of the cortex in the frontal section, as shown in figure 2. Albino rat

BRAINWEIGHT

CORRECTIONCOEFFICIENT

NUMBED

OF CELLS

IN A VOLUME OF CORTEX, 0.001 MM.^

GROUP

\V. D

in fresh brain

W.D on slide

Lam. pyramid.

Lam. ganglion.

Ganglion cells in lam. gangl.

Observed

Corrected

Observed

Corrected

Observed

Corrected

grams

mm.

m m .

la

0.153

6.45

5.65

1150

775

c

0.154

6.35

5.40

1130

695

b

0.177

6.95

6.26

945

690

0.161

(1/1

14)'

1075

720

II a

0.213

8.40

7.35

830

556

370

248

91

61

b

0.221

7.95

6.50

930

509

393

215

114

62

c

0.261

7.80

7.10

735

554

322

242

104

78

d

0.271

7.75

6.80

726

490

358

242

114

77

e

0.288

8.55

7.05

715

402

424

238

120

67

(Birth)

0.251

(1/1

ley

787

502

373

237

109

69

Ilia

0.311

8.50

7.65

625

456

330

241

112

82

b

0.322

8.70

6.80

730

348

415

198

122

58

g

0.374

8.95

8.40

504

417

270

223

98

82

c

0.390

8.85

7.60

493

312

312

197

104

66

i

0.395

9.10

8.60

401

337

262

220

90

76

0.358

(1/1.13)^

551

374

318

216

105

73

IV b

0.400

9.00

8.50

410

345

258

217

94

79

a

0.402

9.10

7.90

473

309

267

175

^5

62

c

0.420

9.00

8.15

451

334

240

178

74

55

i

0.443

9.15

8.40

424

327

227

176

73

56

d

0.459

9.50

7.95

440

258

250

146

77

45

e

0.466

9.30

9.25

355

348

186

182

59

58

0.432

(1/i

loy

426

320

238

179

79

59

Vi

0.501

9,80

9.20

371

307

199

165

69

57

a

0.525

9.65

9.10

362

303

183

154

67

56

b

0.528

9.90

8.60

365

240

205

134

77

51

c

0.534

10.30

8.25

432

222

228

117

78

40

d

0.537

10.00

8.80

412

281

210

143

71

48

e

. 555

9.90

9.00

368

277

164

123

62

47

74

TABLE Z— Continued

BRAIN WEIGHT

CORRECTIONCOEFFICIENT

NUMBER OF CELLS IN A VOLUME OF

ORTBX, 0.001 MM.'

GROUP

W.D

in fresh brain

W.D

on slide

Lam. pyramid.

Lam. ganglion.

Ganglion cells in lam. gangl.

Observed

Corrected

Observed

Corrected

Observed

Corrected

,

grams

m m .

mm.

Vf

0.558

10.00

8.55

357

223

182

114

79

49

g

0.564

10.10

9.15

326

242

178

132

62

46

h

0.579

10.10

9.05

318

229

194

140

64

46

0.542

{1/1

i3y

368

258

194

136

70

49

Vic

O.GIO

10.15

8.50

325

190

182

106

65

38

a

0.617

10.55

8.65

322

177

200

110

60

33

e

0.690

10.60

9.40

286

199

191

133

58

40

0.639

(.1/1

19)^

311

189

191

116

61

37

Vila

0.740

11.00

9.20

277

186

149

100

48

32

b

0.760

11.20

8.70

300

140

188

88

47

22

0.750

(1/1

24)'

289

163

169

94

48

27

VIII a

0.800

11.15

8.60

302

138

170

78

43

20

h

0.805

10.60

8.30

293

140

168

80

48

23

b

0.822

11.85

10.20

266

170

138

88

38

24

c

0.849

11.40

9.90

242

158

140

92

37

24

k

0.870

11.45

9.60

257

151

152

90

45

26

d

0.898

11.75

10.20

255

167

138

90

38

25

0.841

(1/1

20y

269

154

151

86

42

24

IX d

0.959

11.80

9.70

241

133

156

86

40

22

e

0.960

12.15

10.10

224

130

147

85

39

23

a

0.972

11.95

9.80

220

122

150

83

41

23

(10 days)

0.964

(1/1. 2iy

228

128

151

85

40

23

Xa

1.033

12.40

10.30

223

128

153

88

45

26

b

1.036

12.40

10.15

212

116

136

75

41

23

e

1.051

12.10

9.40

244

115

149

70

43

20

1.040

(1/1 ■

23y

226

120

142

78

43

23

XI a

1.107

12.90

10.20

234

116

150

74

44

22

b

1.189

13.15

10.30

229

110

148

71

49

24

c

1.193

12.70

10.30

220

118

144

77

42

23

d

1 . 195

12.50

9.80

222

107

142"

68

44

21

(20 days)

1.171

(1/1.

26)^

226

lis

146

73

45

23

XII c

1.234

12.95

10.70

210

118

136

76

48

27

a

1.273

12.90

9.10

248

■ 87

171

60

55

19

1.253

(1/1. 3iy 1

229

103

154

68

52

23

TABLE 3— Concluded

BRAIN

WEIGHT

CORRECTIONCOEFFICIENT

NU.MBER

OF CELLS

IN .V VOLUME OF CORTE.X, 0.001 MM. 3

GROUP

W.D

in fresh brain

W. D on slide

Lam. pyramid.

Lam. ga

nglion.

Ganglion cells in lam. gangl.

Observed

Corrected

Observed

Corrected

Observed

Corrected

grams

m in .

m m .

XIII a

1.301

13.20

10.25

212

99

177

83

56

26

g

1.307

12.70

10.00

205

100

163

80

52

25

b

1.327

13.35

9.70

243

94

180

69

60

23

c

1.346

13.15

9.85

218

92

174

73

57

24

h

1.392

13.10

10.90

190

110

140

81

50

29

1.335

(1/i

29)3

214

99

167

77

55

25

XIV a

1.412

13.65

10.30

212

91

164

71

58

25

e

1.441

13.10

9.20

248

86

176

61

63

22

b

1.483

13.80

10.80

218

105

172

82

60

29

1.U5

U/1

■ 34)'

226

94

171

71

60

25

XV a

1.530

13.80

10.80

185

88

134

64

47

23

b

1.542

13.70

10.40

207

90

144

63

49

22

c

1.552

13.50

10.30

183

81

152

67

52

23

d

1.573

13.90

10.60

184

82

130

58

53

24

e

1.574

13.70

10.50

204

93

134

60

52

23

1.55i

(1/1

.30)3

193

87

139

62

51

23

XVI a

1.642

13.80

11.20

170

91

127

68

50

27

g

1.643

13.40

9.50

225

81

148

53

56

20

c

1.647

14.00

10.50

186

79

134

57

55

23

e

1.690

13.45

10.00

207

84

148

61

63

26

1.656

(1/1.33)3

1

197

84

139

60

56

24

XVII f

1.720

13.50

9.60

208

75

151

54

60

22

a

1.721

14.00

11.00

178

86

132

64

55

27

b

1.730.

14.70

12.35

142

84

118

70

44

26

c

1.731

14.40

12.10

144

85

106

63

42

25

1.726

(1/1

.26)3

16%

83

127

63

50

25

XVIII c

1.817

14.00

10.10

188

71

142

53

54

20

a

1.844

15.00

12.10

170

89

126

66

48

25

e

1.855

14.30

10.60

192

78

139

57

60

24

1.839

(.1/1

.32)3

183

79

136

59

54

23

XIX a

1.924

14.10

10.90

174

81

110

51

52

24

1.924

(1/1

.29)3

174

81

110

51

52

24

XX a

2.039

14.80

12.10

150

82

95

52

38

27

b

2.069

14.60

11.70

151

78

96

49

37

19

2.054

(i/i.23y'

151

80

96

51

38

20

76

GROWTH OF THE CEREBRAL CORTEX 77

As already shown (Sugita, '17, '17 a), the longitudinal diameter of the sagittal section (from the frontal pole to the occipital pole), that is L. F, as well as the cortical thickness, are both steadily increasing as the brain weight increases. The thickness of the cortex is one component of its area in the section, the other being obtained by dividing the area by the thickness, and the length thus found is correlated with the longitudinal diameter of the section (L. F) as defined above. The increase of the cortical area will therefore depend on the increase in cortical thickness and the increase in the longitudinal diameter of the section (L. F). Table 4 shows these relations. Column B gives the average brain weight by groups, column C the average corrected area of the cortex (taken from table 1), column D the cortical thickness (Tg) and column F the diameter L. F, all in the fresh condition of the brain and the last two quoted from the data already pubHshed (Sugita, '17, '17 a). In column E is given the ratio C/D or the computed length of the long side, when the cortical area is reduced to a rectangle with the short side equal to the cortical thickness. If these computed lengths are compared with the actual longitudinal diameters of the cerebrum (L. F), given in column F, it is of interest to note that, in brains weighing more than 0.5 gram, the ratios, given in column G as E/F, are quite similar, ranging between 1.16 and 1.25 (average 1.22).i In the newborn or before birth (Group I), the ratio is somewhat higher. So, if necessary, the cortical area in the* sagittal sections may be obtained by the following formula

L.F X T^X 1.22 (L. F and T„ in millimeters)

As the. sagittal cortical thickness in brains weighing more than 1.17 grams increases only slowly, the cortical area in the sagittal section in brains older than twenty days is approximately proportional to the longitudinal diameter of the cerebrum (L. F).

E. The area of the cortex in the frontal section

Reviewing table 2 and chart 1 (graph f), we see that the cortical area in the frontal section increases in the same manner

1 In making comparisons with the Norway rat in part II of this paper, the average ratio given by Groups XIII to XX will be that used. This average is 1.21.

THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 29, NO. 2

78

NAOKI SUGITA

TABLE 4

Showing the relations of the cortical area in the sagittal section to the longitudinal diameter (L. F) of the cerebrum and the cortical thickness. All values for the fresh condition. Albino rat.

A

B

c

D

E

F

G

GBOTTP

BRAIN WEIGHT

CORTICAL

AREA

IN SAGITTAJ.,

SECTION

CORTJCAL THICKNESS

IN SAGITTAL SECTION

c

D

L.F

IN FflESH BRAIN

E F

grams

m m .

mm.

mm.

mm.

r

0.161

AA

0.52

8.5

5.6

1.52

II (birth)

0.251

5.8

0.67

8.7

6.4

1.36

III

0.358

8.3

0.90

9.2

7.4

1.24

IV

0.432

10.1

0.99

10.2

8.0

1.27

V

0.542

12.6

1.14

11.0

8.9

1.24

VI

0.639

15.5

1.29

12.0

9.6

1.25

VII

0.750

18.1

1.43

12.7

10.4

1.22

VIII

0.841

20.1

1.48

13.6

11.0

1.24

IX (10 days)

0.964

21.7

1.55

14.0

11.6

1.21

X

1.040

23.5

1.59

14.8

12.0

1.23

XI (20 days)

1.171

26.6

1.72

15.5

12.5

1.24

XII

1.253

26.1

1.75

14.9

12.8

1.16

XIII

1.335

27.6

1.72

16.0

13.0

1.23

XIV

1.445

28.2

1.70

16.6

13.3

1.25

XV

1.554

28.7

1.76

16.3

13.7

1.19

XVI

1.656

29.2

1.77

16.5

14.1

1.17

XVII

1.726

31.1

1.79

17.4

14.3

1.22

XVIII

1.839

32.8

1.86

17.6

14.7

1.20

XIX

1.924

32.3

1.80

17.9

15.0

1.19

XX

2.054

33.7

1.80

18.7

15.3

1.22

Average (Groups V

-XX)

1.22

Average (Groups X

III-XX) .

1.21

as in the sagittal section though more slowly. The cortical area in the frontal section is a product of the cortical thickness (7",,) and the length of the cortex along the cerebral surface. This surface line of the cortex in the frontal section may be regarded as a part of a circle and its length may be taken as proportional to the length of the radius or the measurement W. D (the frontal diameter of the cerebrum), which was measured across the section horizontally (Sugita, '17). As shown in table 5,

GROWTH OF THE CEREBRAL CORTEX 79

which is comparable with table 4, the relative value C/D or

-, — and the ratio of this value to W. D were

Cortical thickness

calculated. The ratio, given in column G, table 5, falls between

0.85 and 0.99 (average 0.91)^ in brains weighing more than 0.5

gram, but shows a tendency to gradually increase as the brain

weight increases. In the newborn or before birth (Group I)

it is somewhat higher. If the average ratio be taken as usable

for all groups, as in the case of the sagittal section, the cortical

area in the frontal section may be approximately obtained by

the following formula:

If. D X T^ XO.91 (W. D and T^, in millimeters)

As, in brains weighing more than 0.95 gram, the cortical thickness in the frontal section (Tp) varies only slightly, the cortical area in the frontal section in these brains will be practically proportional to the frontal diameter of the cerebrum {W. D). The agreement of the calculated with the observed values is however not so good as in the case of the sagittal section.

F. The area of the entire frontal section

In chart 1, the graph F, representing the total area of the frontal section, is accompanied by a dotted line T, which represents the value of the square of the cube root of the brain weight (in grams). Theoretically, under the assumption that the specific gravity of the brain remains the same throughout the life, the latter should run a similar course to the former, if the brain enlarges proportionally in all dimensions as it grows. Between Groups II to XIV, both curves take nearly the same course, if some slight discrepancies in the observed values are neglected. But in brains weighing more than 1.4 grams, the differences become so distinct, that they can no longer be regarded as due to errors in measurement. This is probably due to the fact that the brain is not enlarging proportionally in all diameters,

- In making comparisons with the Norway rat in part II of this paper, the average ratio given by Groups XIII to XX will be that used. This average is 0.93.

80

NAOKI SUGITA

TABLE 5

Showing, in columns A to E, the relations of the cortical area in the frontal section to the frontal diameter of the cerebrum iW . D) and the cortical thickness, and, in columns H to J, the relations of the total area of the frontal section and the frontal diameter of the cerebrum. All values for the fresh condition. Albino rat.

A

B

c

D

E

F

G

H

I

J

GROUP

BRAIN WEIGHT

CORTICAL AREA

INFRONTAL SECTION

CORTICAL THICKNESS INFRONTAL SECTION

D

W. D

IN

FRESH MRAIN

E F

TOTAL AREA

OF FRONTAL SECTION

SQUARE

OF

W. D

gra7ns

irim.'^

m m .

mm.

m m .

mm.^

7)1 m."

I

0.161

3.9

0.56

7.0

6.6

1.06

11.9

43.6

0.27

Ilfbirth)

0.251

5.7

0.78

7.3

7.7

0.95

17.0

59.3

0.29

III

0.358

8.0

1.02

7.9

8.7

0.91

20.6

75.7

0.27

IV

0.432

9.1

1.11

8.2

9.3

0.88

22.4

86.5

0.26

V

0.542

11.7

1.33

8.7

10.1

0.86

26.9

102.0

0.26

VI

0.639

14.4

1.55

9.3

10.6

0.88

31.1

112.4

0.28

VII

0.750

16.4

1.74

9.5

11.2

0.85

32.6

125.4

0.26

VIII

0.841

18,4

1.82

10.1

11.6

0.87

38.9

134.6

0.29

IX (10 days)

0.964

20.4

1.86

11.0

12.1

0.91

42.3

146.4

0.28

X

1.040

20.8

1.82

11.4

12.4

0.92

44.2

153.8

0.29

XI (20 days)

1.171

21.7

1.91

11.4

12.7

0.90

45.7

161.3

0.28

XII

1.253

23.0

1.91

12.0

13.0

0.92

47.2

169.0

0.28

XIII

1.335

23.2

1.94

12.0

13.2

0.91

50.2

174.2

0.29

XIV

1.445

24.8

1.99

12.5

13.4

0.93

52.3

179.6

0.29

XV

1.554

24.3

1.97

12.3

13.5

0.91

54.0

182.3

0.30

XVI

1.656

24.3

1.94

12.5

13.7

0.91

54.9

187.7

0.29

XVII

1.726

24.6

1.90

12.9

13.8

0.94

56.4

190.4

0.30

XVIII

1.839

26.0

1.97

13.2

14.1

0.94

58.9

198.8

0.30

XIX

1.924

24.8

1.83

13.5

14.3

0.94

57.0

204.5

0.28

XX

2.054

24.9

1.72

14.5

14.6

0.99

63.4

213.2

0.30

Average (Groups

^-XX)

0.91

0.28

Average (Groups ]

^111-5

x) . . . .

0.93

the increase in the frontal diameter being retarded relative to the sagittal diameter in brains weighing more than 1.4 grams (Sugita, '17).

If, as given in columns H and I, table 5, the area of the total frontal section is compared with the square of W. D of the corresponding brain group, the above inference will be supported by the fact that the ratio, given in column J of the same table,

GROWTH OF THE CEREBRAL CORTEX 81

is almost equal throughout all brain weight groups, swinging within the narrow limits of 0.26 to 0.30.

G. Percentage of the area of cortex in the total area of the frontal section (one hemicerehrum)

Figure 2 shows the outline of the frontal section. In the section we see as the principal divisions the cortex, the striatum, the thalamus, the capsula externa and the lateral ventricle, and, among these, the cortex and the striatum stand in marked contrast. In the young brains, the lateral ventricle is wide. This cavity was not included in the measurement of the area. In the wall of it, especially at the dorso-lateral corner, there are seen masses of dividing cells and of neuroblasts, which are due to migrate into the cortex. But in the older brains weighing more than 1.1 grams, the ventricular wall is almost free from dividing cells and the cortex is no longer receiving new cells. By determining the percentage of the cortical area to the total area of the frontal section, we may obtain some clue as to mass relation of the cortex to the other structures seen in the frontal section.

As previously given in table 2, the cortical area in the frontal section amounts to 34 per cent of the total area at birth. It increases from birth up to bi'ains weighing 0.7 to 1.2 grams, when the percentage reaches its highest figure, that is, 50 or sometimes 51, on the average 48 per cent. After this stage, the percentage slowly diminishes as the brain weight increases, and, at full maturity, it reaches 44 per cent or less; even 39 per cent in an old brain weighing more than 2.0 grams. This means clearly that the cortical area increases rapidly by receiving new cells from the matrix and at the same time by the enlargement and separation of the cell bodies, during the first phase, covering the first ten days after birth.

In this phase, as a matter of fact, the remainder of the section is for the most part composed of the matrix and migrating cells, the central nuclei being not yet so largely developed. The transitional layers, or the areas previously occupied by the

OZ NAOKI SUGITA

transitional layers, which will be replaced by the capsula externa, are relatively wide during this phase.

After twenty daj^s, when the brain has attained nearly the weight of 1.17 grams, the remainder of the section (the central nuclei and the white substance) increases more rapidly than the cortical area and the group of proliferating cells in the ventricular wall disappears. The percentage of the cortical area to that of the whole section consequently decreases under these conditions, though the absolute value of the cortical area is steadily increasing.

From the mode of the changes in the percentage value of the cortical area, we may conclude that, in the albino rat, at least, the period during which the brain weight increases from 0.25 gram (birth) to 1.2 grams (about 20 daj^s), is the period when the cortical elements are principally produced, matured and arranged, and that the cortex is precocious in its construction. The growth or construction of the remaining parts in the frontal section, so far at least as this is expressed by increase in volume, is relatively retarded or delayed until the cortex has acquired all its characteristic elements.

H. The volume of the entire cortex

The true volume of the entire cerebral cortex can not be measured by the methods here used. It will require a special study for that purpose. My present object is to obtain relative values for the cortical volume and a record of the change in these relative values according to brain growth. If the data for the area of the cerebral cortex as measured by me in the two typical sections be reduced to a simple geometrical form, it will be very easy to compare the changes in the computed volume in successive brain weight groups. As already mentioned, the cortical area in the sagittal and the frontal sections, which sections cross one another at right angles, may be reduced to rectangles which have as the long side the lengths proportional respectively to the sagittal and the frontal diameters of the cerebrum (L. F and W. D), and as the short side the cortical

GROWTH OF THE CEREBRAL CORTEX

83

thicknesses {T^ and Tp). For the present purpose, the mean cortical thickness (T) may be substituted for both the foregoing values of the cortical thickness, when the brain weight is the same, because T falls at the mean of the T^ and T^, so that the gain in T^ would be compensated by the loss in T^ (fig. 3). As a consequence the volume of the cortex may be represented by an index value, the formula for which follows.^

L.FX W. D XT

(all in millimeters)

CKNES5 OF CORTEX

Fig. 3 The solid lines show the simplified geometrical form used to indicate the volume of the entire cortex, which is assumed to be proportional to the rectangular form designated by dotted lines in the figure. The volume of the rectangular figure, which was obtained by the value: L. F y, W . F X T, has been tabulated in column F, table 6, and plotted as graph LWT in chart 2.

The values thus obtained — which mean the actual volume of the rectangle denoted by dotted lines in figure 3 — stand in a fixed relation to the true cortical volume which is denoted by solid lines in the same figure, as far as the latter retains a similar form during growth.

5 In this formula, the coefficients 1.22 and 0.91, which were empirically determined, were eliminated, because these coefficients are fixed throughout all the groups to be compared. For Groups XIII to XX, the coefficients are respectively 1.21 and 0.93, and these will be taken into consideration when comparison is made between the Albino and the Norway rats.

8-i

NAOKI SUGITA

TABLE 6

Giving for each brain weight group the average brain weight, ratio in cerebral volume, computed cortical volume and the data used to obtain the computed cortical volume, and ratio in cortical volume

A

B

C

D

E

F

G

BRAIN WEIGHT GROUP

BRAIN WEIGHT

RATIO

OF

VOLUME

OF

CEREBRUM

L.F

IN FRESH BRAIN

W. D

IN FRESH BRAIN

AVERAGE CORTICAL THICKNESS

L. FX W. DXT,

COMPUTED VOLUME

OF CORTEX

RATIO OF

COMPUTED

VOLUME

OF COKTEX

grams

m m .

m m .

m m .

?n»i.'

I

0.161

5.6

6.6

0.54

19.96

II (birth)

0.251

1.00

6.4

7.7

0.73

35.97

1.00

III

0.358

1.34

7.4

8.7

0.96

61.81

1.72

IV

0.432

1.66

8.0

9.3

1.10

81.84

2.28

V

0.542

2.12

8.9

10.1

1.24

111.46

3.10

VI

0.639

2.53

9.6

10.6

1.42

144.50

4.02

VII

0.750

3.12

10.4

11.2

1.58

184.04

5.12

vni

0.841

3.50 '~

11.0

11.6

1.65

210.54

5.85

IX (10 days)

0.964

4.04

11.6

12.1

1.71

240.02

6.67

X

1.040

4.10

12.0

12.4

1.72

255.94

7.12

XI (20 days)

1.171

4.61

12.5

12.7

1.82

288.93

8.03

XII

1.253

4.80

12.8

13.0

1.8S

304.51

8.47

XIII

1.335

5.17

13.0

13.2

1.83

314.03

8.73

XIV

1.445

5.40

13.3

13.4

1.85

329.71

9.17

XV

1.554

5.89

13.7

13.5

1.87

345.86

9.62

XVI

1.656

6.05

14.1

13.7

1.86

359.30

9.99

XVII

1.726

6.44

14.3

13.8

1.85

365.08

10.15

XVIII

1.839

6.72

14.7

14.1

1.92

397.96

11.06

XIX

1.924

6.91

15.0

14.3

1.82

390.39

10.85

XX

2.054

7.85

15.3

14.6

1.76

393.15

10.93

1 T, here entered, is the mean value of Ts and T^, previously given in tables 4 and 5 and is not the general average thickness of the cortex of the sagittal, frontal add horizontal sections formerly presented in my second paper in this series (Sugita, '17 a) .

Table 6 shows the values for the cortical volume computed by the above method and the ratios, the cortical volume at birth being taken as the unit of the comparison.

Chart 2 (graph LWT) shows graphically the ratios obtained (table 6, column G), accompanied by the graph (graph LWH) which shows the increase in volume of the cerebrum (table 6, column B). The volume of the cerebrum was computed according to my previous procedure (Sugita, '17). From this

GROWTH OF THE CEREBRAL CORTEX

86

chart we see that the cortical volume increases more rapidly than the entire cerebral volume, until the brain attains the weight of 1.17 grams (20 days) (see crosses in chart 2), If we take these marks as the starting points, then the cerebral volume increases to about 1.7 times at full maturity and in the same way the cortical volume increases to about 1.4 times compared with the value at twenty days (table 6). So, it may be stated that after twenty days the increase in cortical volume becomes

^2

n

10 9

X

y—

~-«v,_

-:^

'°N.

■ L\A

T

-^

y^"

-■

^^

"~tf'

^'^

"^s^

"°"

■

■Tiu

VT°

_^-'

x^

^•^

-^^

6

\

/

/'"

y

/

^'^

f

6

5

4

-^

A

y

y

,,,

'-"

•'■

/

\

\

/

/•'

,..„

'-

'

\

\

/

/

,

'-'■'

"■"

>

\

__,

,-'

'

/

^'

V

^-^

~^.-_

^

— »—

-" —

-.-_

'

N

^

^

0.1 0.2 B 0.3 0.4 05 0.6 0.7

09 10 11 12 13 14- 15 ife i? 18 19 2.0 Jmi

Chart 2 Showing the ratios of the values for the cortical volume, the volume of the cerebrum, the cell density in two unit volumes and the computed number of nerve cells in the entire cerebral cortex of the albino rat, according to the

brain weight. • • LWT, The ratios of the computed volume of the cerebral

cortex, the volume at birth being taken as the unit. Based on the data in table

6. . • LWH, The ratios of the volume of the entire cerebrum,

the volume at birth being taken as the unit. Based on the data presented in a former paper (Sugita, '17) and given also in table 6. X XN, The cell density in two unit volumes of the cortex. Based on the data given in column C, table 7, as N", and plotted here according to the values corresponding to one onehundredth of the number given in column C, table 7. •■ — •" * NLWT, The ratios of the computed number of nerve ce»lls in the entire cortex, the value at birth being taken as the unit. Here the unit chosen on the ordinate is 5. The data are given in column E, table 7.

86 NAOKI SUGITA

slower and is somewhat less in rate than the increase in cerebral volume or brain weight, as is also seen in the graphs given in chart 2.

/. Number of cells in a unit volume of the cortex

In the lamina pyramidalis of the newborn Albino brain, at a dorso-lateral part of the pallium, where, in the frontal section, the cell count was irfade (fig. 2, VII), there were in the fresh condition about 500 pyramids crowded in a unit volume of 0.001 mm.^' This number decreases, as the brain grows, and falls to 110 in a brain weighing about 1.2 grams (20 days) (table 3). In a brain weighing about 1.5 grams (50 days), the number has dropped nearly to 90, from which it is only slightly reduced in the heavier brains. In an old rat, whose brain weighs more than 2.0 grams, the number is about 80, or less than one-sixth the number at birth. According to another study, which will be published later, the size of the cell body and of the nucleus of the pyramids in the lamina pyramidalis, measured at this same locality, increases very rapidly during the first ten days after birth, till the brain has attained 0.9 gram in weight, when these structures reach their maximum size (Cell body 16/x X 20ju; Nucleus 14;u X 15m). After this stage the cell body and the nucleus ar'e mature in their nucleus-plasma relation, but still changing their chemical composition, as revealed by the stains, while the neuron as a whole is still growing as shown by the developing axon and the dendrites.' This fact is in accord with the observation that the number of pyramidal cells in the lamina pyramidalis decreases rapidly after birth, until the brain weight reaches about 0.9 gram (10 days), after which the rate of decrease becomes slow.

The change in cell number in a given volume of the cortex during the growth of the brain is determined by two main factors: (1) the enlargement of the cell body proper and the growth of the cell branches and (2) the development of the intercellular structures (that is, incoming nerve fibers, neuroglia, blood vessels) and myelin formation, separating the cells more and more from each other.

GROWTH OF THE CEREBRAL CORTEX 87

As to the cells in the lamina ganglionaris, the relation is somewhat different from that just described. The total number of cells, including both the small and large pyramids, decreases relatively rapidly after birth, until the brain weight reaches 1.25 grams (25 days). It then shows a slight increase (table 3, Groups XIII and XIV), but decreases again by slow steps and remains almost fixed after 35 days (brain weight 1.4 grams) at 60. Finally, in old rats, only 50 cells were counted in a unit volume of 0.001 mm. ,3 or about one-fifth the number at birth.

If the number of the large pyramids alone is considered, then the number decreases rapidly from birth to a brain weight of 0.8 gram (9 days). After this, it decreases slightly and remains almost fixed at 23 up to a brain w^eighing 1.2 grams. In brains weighing 1.3 to 1.5 grams it shows a tendency to increase slightly for a time — corresponding to the increase in total number of cells in this layer (above mentioned) — but finally becomes fixed again at 23 to 24 throughout maturity. In old age, it has diminished to 20 or about two-sevenths the number at birth. The large ganglion cells attain nearly their full size (Cell bod}^ 21^ X 28m; Nucleus 18m X 19m) at 0.9 gram in brain weight (10 days), almost at the same time as the small pyramids.

I can not, from the data at hand, satisfactorily explain the increase in cell number in the lamina ganglionaris in the period during which the brain grows from 1.2 grams to 1.4 grams in weight. This fact might however have some connection with the chemical structure of the cells and consequently be related to a change in reaction to the reagents used, so that the size of the large pyramids, after having attained a maximum (21m X 28m) at a brain weight of 0.9 gram, diminishes slightl}^ at the same time that their response to the stain changes somewhat, measuring only 20m X 27m at a brain weight of 1.3 to 1.4 grams, after which they again enlarge to a full size of the cell body (sometimes over 23m X 30m). In the carbol-thionine staining the sections from brains weighing less than 1.0 gram show a violet tone, those from brains weighing more than 1.2 grams a blue tone while those from brains weighing 1.0 to 1.2 grams are intermediate in tone. We shall pass over this question now,

88 NAOKl SUGITA

as a detailed description of the size of each cell type and its mode of enlargement according to age will be the theme of a later paper.

To represent the relative cell density in the cerebral cortex for each brain weight group, the sum of the cell numbers in the lamina pyramidalis and the lamina ganglionaris, given in table 3, was used, in order to balance, in some measure, the inequality of the cell distribution. These values are given in table 7, column C, and in chart 2 (graph N). Both table and chart show that the number of nerve cells in a unit volume of the cortex decreases verj^ rapidly during the first ten days after birth (up to the brain weight of 0.95 gram) and after that time it decreases slowly but steadily as the age advances. The cell number at maturity is nearly one-fifth the value at birth.

J . Values for the co7nputed yiumher of nerve cells in the entire cerebral cortex, according to brain weight

The number of nerve cells given in table 3 does not means the actual volume of complete cells contained in a unit volume, because the parts of cells which showed a nucleus but no nucleolus in the section were also counted. In spite of this, the number in the table indicates fairly the relative number of cells or the relative cell density at different ages in the localities examined, and from this we may be able to get some indication as to the number of nerve cells in the entire cerebral cortex.

If the actual number of cells in a unit volume be proportional to the number of cells counted, the number of cells in the entire cerebral cortex may be indicated (theoretically) by this number multiplied by the number obtained by dividing the volume of the entire cerebral cortex by the unit volume.

The actual volume of the cortex was not measured, but the computed volume is indicated by the following formula, as explained already.

L.F XW.D XT (all in millimeters)

So, if N means the cell number in a unit volume (for example,

GROWTH OF THE CEREBRAL CORTEX 89

N is 240 for Group VIII, as shown in table 7, column C), the relative value of the number of nerve cells in the entire cortex may be computed by the following formula.^

NxL.FxW.DxT (L.F, W.D and T, in millimeters)

The results of this computation are shown in table 7 and in chart- 2 (graph NLWT), where the necessary data were all taken from the present or former papers and the relative value of N X L. F X W. D X T is calculated. For N, the corrected sum of the cell numbers in the lamina pyramidalis and in the lamina ganglionaris, given in table 3, was used (table 7, column C). The results are quite interesting. As seen from table 7, columns D and E, and chart 2 (graph NLWT based on column E,), the relative value of the computed number of cells in the entire cortex increases rapidly from birth to a brain weighing 0.9 gram (about 10 days), and then for a while the increase becomes slow up to a brain weight of 1.17 grams (20 days), attaining at this time nearly the complete number of nerve cells (see graph NLWT, mark X in chart 2) . After having passed this phase, the value for the number of cells remains almost constant throughout the life. The average of the values for Groups XI-XX in table 7 is 530, so that between birth and maturity the number of cells counted has increased two times, but nearly al^ of this increase has taken place during the first ten days of life. These results coincide v.ery well with the conclusions of Allen ('12), that in the cerebrum mitosis continues with diminishing activity to the 20th day after birth.

'^ By this computation the number of cells in the entire cortex will be equal to the number of times the unit of volume, 0.001 mm.' in which the cells were counted, is contained in the entire volume of the cortex, multiplied by the number of cells in a unit volume. The number of cells designated by N is however the sum of the numbers in two unit volumes, that is, the number in one unit volume of the lamina pyramidalis plus the number in one unit volume of the lamina ganglionaris.

Since the numbers of cells used, N, is that in two unit volumes, the foregoing product must be divided by two. As dividing the volume of the cortex by 0.001 is equivalent to multiplying it by 1000, and as the product must be divided by two, the operation may be expressed as follows:

N X L. F X W. D X T X oOO = Number of cells

90

NAOKI SUGITA

TABLE 7

Giving the computed number of nerve cells in the entire cerebral cortex, obtained on the basis of the measurements given in this series of studies. The ratio of the mimber of cells of each later group to that of Group 11 (birth) is also given

A

B

C

D

E

COMPUTED

BRAI.V WEIGHT GROUP

BRAIX WEIGHT

COMPUTED

VOLUME OF

CORTEX

L.FX ir. D X T

SUM OF XOS. OF CELLS I.V L.\M. PYR. AXD ■LAM. GAXG. IX TWO UNIT

NUMBER OF

CELLS IN CORTEX,'

A XL.FX W. D XT

RATIO

OF NU.MBER

OF CELLS

VOLUMES, K

^ 100

gra m s

mrn.^

II fbirthi

0.251

35.97

739

265.8

1.00

III

0.358

61.81

590

364.7

1.37

IV

0.432

81.84

499

408.4

1.54

^'

0.542

111.46

394

439.2

1.65

VI

0.639

144.50

305

440.8

1.66

VII

0.750

184.04

257

473.0

1.78

VIII

0.841

210.54

240

505.3

1.90

IX flO days)

0.964

240.02

213

511.2

1.92

X

1.040

255.91

198

506.8

1.91

XI (20 davs)

1.171

288.93

186

537.4

2.02

XII

1.253

304.51

171

520.7

1.96

XIII

1.335

314.03

176

552.7

2.08

XIV

1.445

329.71

165

544.0

2.05

XV

1,554

345.86

149

515.3

1.94

XVI

1.656

359.30

144

517.4

1.95

XVII

1.726

365.08

146

533.0

2.01

XVIII

1.839

397.96

138

549.2

2.07

XIX

1.924

390.39

132

515.3

1.94

XX

2.854

393.15

131

515.0

1.94

Average (Groups !X

i-xx) ....

530.0

2.00

Average (Groups ^

iii-xx) ..

530.2

2.00

1 As explained in a footnote (footnote 4j, the actual number of cells contained in the computed volume of the cortex should be N X L. F X W. D X T X 500, but, for the convenience, 1/100 of N X L. F X W. D X T, or 1/50,000 of the actual numbet of cells contained in the computed volume, was given here as the computed number of cells in the cortex.

The above statement that between birth and maturity the nmnber of nerve cells in the entire cortex has increased twofold, does not necessarily mean that the additional cells have been all newly formed after birth. As a matter of fact, we see,

GROWTH OF THE CEREBRAL CORTEX 91

in the sections of the newborn brains, many immature cells, the indifferent cells and the neuroblasts, crowded densely together in the ventricular wall and in the transitional layers and these are all migrating to the cortex. The number of cells in the cortex is increased after birth by receiving these cells already formed but lying at birth still outside of the cortex proper, besides by receiving the cells which are newly formed after birth. So the nerve cells, destined for the cortex, are largely present in immature form in the cerebrum at birth, but lie outside of the cortex proper, while the actual number of cells formed after birth may amount only to a small fraction of the total number of nerve cells in the cortex at maturity, though there is active mitosis during the first days after birth.

I have previously recognized three developmental phases in the growth of the cortex in thickness (Sugita, '17a), as f ollow^s :

First phase, from birth to the 10th day.

Second phase, from the 10th to the 20th day.

Third phase, from the 20th to the 90th day.

The first and the second phases here given may also be applied, without any modification, to the changes in cell number in the cerebral cortex, while the third phase does not appear in this connection.

IV. CONCLUSIONS

In an earlier study on the cerebral cortex of the albino rat (Sugita, '17 a), I stated that the cerebral cortex attains nearly its full thickness at the age of twenty days, before myelination in the cortex had begun, and that the organization of the cerebral cortex might be considered as precocious, having been provided with all its mechanisms at the time of weaning. At this age, the brain weight is only a little more than one-half the weight at maturity. Size, volume and weight of the entire brain are^ all midway in their growth, but there have appeared no striking changes by which we might guess from the gross appearance of the brain anything about the numerical completeness of its cortical elements. Just at this stage, however, cell division in the cerebrum has almost ceased (Allen, '12).

92 NAOKI SUGITA

From the data now available, I conclude that, in the albino rat, the cerebral cortex exhibits the complete number of nerve cells at about the 20th day after birth, at which age some of the cells have attained their full size. The area of the cortex in the sagittal and in the frontal sections has shown a continuous increase throughout life and no radical change in rate occurs at this time. But, if the thickness of the cortex be taken into consideration and the volume of the entire cortex be calculated, it becomes clear that the entire volume of the cerebral cortex has stopped the more active increase, which it made earlier, at about the 20th day, and after that the increase becomes slow, and lower in rate than the increase in the volume of the cerebrum. If, further, the' cell density in the cortex be considered, it is found that the number of cells as computed for the cerebral cortex (table 7, column E) increases rapidly, especially during the first ten days after birth, but exhibits nearly its complete number at the age of twenty daj^s, after which it shows no significant change.

We may conclude therefore that the cerebral cortex has been completely organized at the age of about twenty days, and that the further development of the cortex does not involve an increase in cell number, but involves mainly the maturing of elements already provided. The education of the cerebral cortex as a whole might properly be said to begin after this age, the preceding period having been largely one of preparation or construction. It is of interest to note that this epoch corresponds to the weaning time of the rat.

According to the study of Donaldson ('08) on the comparison of the albino rat and man, the rat grows thirty times as fast as man. When however the brain of the rat is to be compared with that of man, it must be remembered that at birth the human brain is somewhat more mature and corresponds in organization not with the rat brain at birth but at five days of age (Donaldson MS.). This being the case, the rat cortex at the 20th day of postnatal life probably corresponds with the human cortex at the 15th month (20 less 5). This conclusion has not yet been tested.

GROWTH OF THE CEREBRAI CORTEX 93

V. SUMMARY

1. Empl-oying the sagittal and the frontal sections of 78 albino rats, which were formerly used for the investigation on the thickness of the cerebral cortex (Sugita, '17 a), I made further measurements on the area of the cortex in these sections and counted at a fixed locality the number of nerve cells contained in a unit volume of 0.001 mm,,^ in brains from birth to maturity.

2. The observed data were all corrected to the values for the fresh condition of the material, by the use of the correctioncoefficients based on the observations. The results were grouped and averaged according to the brain weight groups and the postnatal growth changes systematically analysed.

3. The area of the cortex shown in the sagittal section is found to be proportional to the value L. F X T^, where L. F is the longitudinal diameter of the cerebrum and T^ is the average thickness of the cerebral cortex in the sagittal section. The actual area (after five days of age) may be calculated by the formula: L. F X T^ X 1.22 (L. F and T^, in millimeters), where 1.22 is a constant coefficient which was empirically determined (see table 4, column G).

4. The area of the cortex shown in the frontal section (of one hemicerebrum) is found to be proportional to the value W.D X T^, where W. D is the frontal diameter of the cerebrum and T^ is the average thickness of the cortex in the frontal section. The actual area (after five days of age) may be calculated by the formula: W.D xT^ X 0.91 {W.D and T^, in millimeters), where 0.91 is a constant coefficient which was empirically determined (table 5, column G).

5. The percentage of the total' area of that frontal section which is represented by the cortical area is least at birth (34 per cent) and increases as the age advances till it reaches the maximum (50 per cent) at the period of 7 to 20 days (brain weight 0.75 to 1.25 grams). It then decreases, slowly and at maturity is less than 44 per cent (table 2). This means that durihg the first 7 days the cortex is increasing in area more rapidly than the remainder of the section, while during the

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 2

94 NAOKI SUGITA

following 13 days its rate of increase is similar to that of the remainder. After 20 days the rate of increase for the remainder surpasses that for the cortex.

6. The actual volume of the cortex could not be obtained by the use of the data now available, but the cornputed volumes of the cerebral cortex at different ages (comparable among themselves), may be found by the use of the formula: L. F X W.D xT (all in millimeters), where L. F is the longitudinal diameter of the cerebrum, W. D is the frontal diameter of the cerebrum and T is the average thickness of the cortex. The volume increases most rapidly during the first ten days after birth and the rate of increase in the cortical volume continues to surpass the rate of increase in the entire cerebral volume, during the first twenty days. After twenty days the cortex increases at a somewhat lower rate than the increase of the entire cerebrum in volume (chart 2).

7. The number of cells contained in a unit volume of 0.001 mm.-^ of the cortex indicates the cell density of the locality where the count was made. In the lamina pyramidalis the pyramids are most crowded at birth and the number in the unit volume decreases rapidly during the first ten days after birth. After twenty days it decreases slowly but steadily, the number at maturity being about one-sixth the number at birth. As for the lamina ganglionaris, the total cell number in the unit volume (the small and the large pyramids taken together), is at its highest value at birth. It decreases relatively rapidly during the first twenty-five days after birth, then is slightly increased for a time, after which it decreases again slowly and at full maturity it shows about one-fifth the number present at birth. Taking the large ganglion cells alone, we find that the number decreases rapidly during the first eight to ten days, then remains the same up to twenty days, after which it decreases again, showing two-sevenths the initial number at full maturity. The decrease in cell density according to brain growth is due to the enlargement of cell bodies, the deA'elopment of cell attachments, the separation of cells from each other through myelination, ingrowing fibers and other changes. The average cell density,

GROWTH OF THE CEREBRAL CORTEX 95

represented by the sum of the numbers in the lamina pyramidalis and the lamina gariglionaris, given as A^ in table 7, decreases rapidly during the first ten days and after that the decrease becomes very slow and steady, showing at maturity a density of about one-fifth of that at birth.

8. The computed value for the number of cells in the entire cerebral cortex may be determined by the formula: N X L. F X W.D X T {L.F, W.D and T, all in millimeters), where L. F is the longitudinal diameter of the cerebrum, W. D the frontal diameter of the cerebrum, T the average thickness of the sagittal and frontal cortex and A^ the average number of the nerve cells in two unit volumes of the cortex, at the particular locality (locality VII) where the counts were made. This computed value for the number of nerve cells in the entire cerebral cortex increases rapidly during the first ten days, at the end of which period it attains nearly 1.9 times the value at birth. During the following ten days, it increases slowly but steadily, and it attains its complete number at the age of twenty days (brain weight 1.17 grams). After this age the number of nerve cells is almost constant. The number of cells at maturity is twice the number at birth.

It is recognized that this conclusion concerning the number of nerve cells in the cortex at various ages is based on enumerations in only two cortical layers at but one locality, and that on this ground its general value might be questioned. When it is recalled however that table 11 in a preceding study on the growth of the cortex in thickness (Sugita, '17 a) shows all the localities measured in the cortex to undergo the same relative increase in thickness between birth and maturity, and always to stand in the same relation to one another, the doubts with regard to the general value of these particular results are largely removed.

9. Considered all together, the data on the development of the cerebral cortex indicate that it has been completely organized in the albino rat at the age of twenty days. The further development after this age represents a maturing of the elements. The completion of the cerebral organization corresponds to the

96 NAOKI SUGITA

weaning time of the rat.. If the cerebral organization of the rat brain at five days of age is similar to that of the man at birth, and the growth processes in the rat are thirty times as rapid as in man, then the completion of the cortex which occurs in the rat brain at twenty days should occur in the human brain at about fifteenth month of age.

PART II

ON THE AREA OF THE, CORTEX AND ON THE NUMBER OF CELLS IN A UNIT VOLUME, MEASURED ON THE FRONTAL AND SAGITTAL SECTIONS OF THE BRAIN OF THE NORWAY RAT (mUS NORVEGICUS), AND COMPARED WITH THE CORRESPONDING DATA FOR THE ALBINO RAT

VI. INTRODUCTION

In the Part I of this paper, I have presented the data on the area of the cerebral cortex measured on the sagittal and the frontal sections of the Albino rat brain and on the number of nerve cells in a unit volume of the cerebral cortex, and, by calculations based on these data, I have come to the conclusion that the entire volume of the cerebral cortex is increasing most rapidly during the first ten days after birth, while from twenty days onwards it increases at a lower rate than the entire cerebral volume. Further, the computed number of nerve cells in the entire cerebral cortex also increases very rapidly during the first ten days after birth and attains nearly its complete number at the age of twenty days.

I now wish to compare these relations in the Albino with those in the Norway rat, in the same manner as I have already done in the matter of the growth of the brain in size (Sugita, '18) and of the thickness of the cortex (Sugita, '18 a).

Employing for the Norway brains the sections on which the cortical thickness was measured earlier and for which the individual body measurements have been already given in table 1 in mj^ fourth paper (Sugita, '18 a), I have measured the area

GROWTH OF THE CEREBRAL CORTEX 97

of the cortex in the sagittal and the frontal section, following methods of measurement just described (part I) in the case of the Albino rat. Correction of the observed values to the values in the fresh condition of the material was also made by the use of the correction-coefficients obtained in the same way as those used for the Albino.

This study was made between March and May, 1917, at the Wistar Institute of Anatomy and Biology.

VII. MEASUREMENTS AND ENUMERATIONS

A'. Area of the cortex in the sagittal section {Nonvay rat)

Table 8 shows the observed and corrected areas of the cerebral cortex in the sagittal section of the Norway brain, also the data for the correction-coefficient for each individual, and the correction-coefficient for each brain weight group. The method of measurement and the positions of the borderlines of the measured area have been already described in part I of this paper, so that the explanations need not be repeated here (fig. 1). Chart 3 (graph s) has been plotted on the basis of table 8.

L. Area of the cortex in the frontal section {Nonvay rat)

Table 9 gives the observed and corrected areas of the cortex and the total area of the frontal section (one hemicerebrum) of the Norway brain with the data for the correction-coefficient for each individual and the correction-coefficient for each brain weight group. It gives also the percentage of the cortical area to the total area of the section. Chart 3 shows also in graphs (graphs F and f) the corrected data given in table 9.

M. Number of nerve cells (Norway rat)

Table 10 gives the observed and corrected number of nerve cells in a unit volume of 0.001 mm.-^ (0.1 mm.- in area and 0.01 mm. in thickness) at a fixed locality (locality VII) of the cortex in the frontal section, for each individual and for each brain weight group. The locality was chosen at a middle part of the cortical band in the frontal section as shown in figure 2, VII,

9.8

NAOKI SUGITA

for the Albino rat. The numbers of cells in the lamina pyramidalis and in the lamina ganglionaris respectively and the number of ganglion cells only in the lamina ganglionaris in five adjoining squares, each 100 micra on each side, were counted and the numbers in the unit volume of 0.001 mm. computed (see part I) and recorded in table 10. The relative cell density

^

F

/

^

— ^

/^

^

.^

^y

/

^

-^'

._.

__.

--

■■"""

r^-—

-^

1

-^/

■ —

■

« 

1 1 1

10 11 1.2 13 14- 15 16 IT 1& 1.9 2.0 2.1 22 23 jws.

Chart 3 Showing the areas of the cerebral cortex in the sagittal and the frontal sections and the areas of the whole frontal section according to the brain weight. Norway rat. This chart is comparable with chart 1, which gives the corresponding graphs for the albino rat. X — . — . — Xs Cortical area in the

sagittal section. • 'f, Cortical area in the frontal section. •——•F, Area of

the whole frontal section. All graphs were based on the data in tables 8 and 9.

represented by the sum of the numbers of nerve cells in the lamina pyramidalis and the lamina ganglionaris is tabulated in table 16, column D, and plotted in chart 4 as graph N' .

VIII. DISCUSSION AND COMPARISON

The foregoing data, treated in a manner similar to that adopted in the case of the Albino (part I), may now be used for discussion and comparison.

GROWTH OF THE CEREBRAL CORTEX

99

TABLE 8

Showing the observed and corrected values of the area of the cerebral cortex in the sagittal section of the Norway rat brain, accompanied by the data for the correction-coefficient in the individual cases and the correction-coefficient for each brain weight group. L. F is the longitudinal diameter of the cerebrum

CORRECTION-COEFFICIENT

BR.\IN WEIGHT

OBSERVED

.\RE.\^ OF CORTEX

CORRECTED

GROUP

L.F

on fresh brain

The same on slide

.\RE.4. OP CORTEX

aravix

mm.'

m m .

m m .

Hi m .2

N XI b

1.155

18.4

11.75

10.40

23.5

a

1.160

17.0

12.10

10.15

24.2

i

1.175

14.2

12.55

9.60

24.3

1.163

16.5

l.'A

?P

24.0

NXII

N XIII a

1.369

16.7

12.95

10.10

27.5

1.369

16.7

l.i

W

27.5

NXIVb

1.407

18.2

13.45

10.50

29.8

g

1.429

16.3

13.05

10.10

27.2

a

1.431

19.1

13.15

10.40

30.6

i

1.431

18.1

13.05

10.25

29.4

e

1.437

15.8

12.80

10.05

25.7

k

1.445

19.2

13.35

10.30

32.3

1.430

17.8

l.i

W

29.2

N XV c

1.517

16.4

12.70

10.10

26.0

e

1.557

17. 3

13.75

10.30

30.8

1.537

16.9

l.t

w

28.4

N XVI a

1.619

17.2

13.50

10.20

30.2

g

1.632

16.8

13.45

9.75

32.0

e

1.636

15.9

13.55

10.00

29.2

1.629

16.6

l.t

w

30.5

N XVII e

1.710

18.8

13.70

10.40

32.6

g

1.721

18.7

13.40

10.20

32.3

a

1.738

16.8

13.60

10.40

28.8

c

1.788

20.1

14.20

11.00

33.5

1.739

18.6

l.i

w

31.8

N XVIII c

1.825

18.1

14.30

10.70

32.4

a

1.833

22.0

14.20

11.50

33.5

1.829

20.1

1.28'

33.0

100

NAOKl SUGITA

TABLE S— Continued

BRAIN- WEIGHT

OBSERVED

AHE.\ OF CORTEX

C ORRECTION-COEFFICIEXT

CORRECTED

GROUP

L.F on fresh brain

The same on slide

ARE.\ OF CORTEX

grains

mm.

mm.

mm.

m m .

N XIX b

1.962

19.9

14.70

11.25

34.1

a

1.981

19.5

14.40

11.00

33.5

1.972

19.7

1.31-'

33.8

NXXc

2.015

20.6

14.55

11.30

34.2

a

2.089

20.7

14.95

11.80

33.3

2.052

20.7

1.28'

33.8

NXXIg

2.156

21.1

15.15

11.90

34.2

d

2.187

20.2

15.30

11.50

35.7

2.172

20.7

l.t

w

35.0

NXXII

N XXIII a

2.345

22.4

14.50

11.50

35.7

2.345

22.4

1.26'

35.7

N. The area of the cortex in the sagittal section. Norway rat compared with the Albino

Table 11 shows the relations between the cortical area in the sagittal section and the longitudinal diameter of the cerebrum (L. F). Column B gives the average brain weight by groups, column C the average area of the cortex in the sagittal section, column D the average cortical thickness in the sagittal section {T ), column F the longitudinal diameter of the cerebrum (L. F), all of these being the corrected values. In column E the value C ; D or relative length of the long side, when the cortical area was reduced to a rectangle with the short side equal to the cortical thickness, appears. iVs shown in column G a.s E IF. these computed lengths show similar ratios when divided by the actual diameters L.F (column F), that is, 1.16 to 1.24 or on the average 1.20 for Groups N XI-N XXIII, but 1.19 for Groups N XIIIJN^ XX.- If necessary, therefore, the cortical area in the sagittal

GROWTH OF THE CEREBRAL CORTEX

101

TABLE 9

Showing the observed and corrected value's of the area of the cerebral cortex and of the total section in the frontal section and the -percentage of the cortical area in the total frontal section of the Norway rat brain, accompanied by the data for the correction-coefficient in the individual cases and the correction-coefficient for the group. W. D is the frontal diameter of the cerebrum,

OBSERVED

CORRECTIONCOEFFICIENT

CORRECTED

PERCENTAGE OP

BRAIN WEIGHT

CORTICAL

GROUP

Area of cortex

Area of total section

W.D

in fresh brain

The

same on

slide

Area of cortex

Area of

total section

AREA IN TOTAL SECTION

gra ms

vim.

»jm.2

mm .

m m .

mm.

mm .2

per cent

NXIb

1.155

13.8

28.1

13.00

10,00

23.4

47.5

49

a

1.160

12.8

27.9

12.70

9.80

21.5

47.0

46

i

1.175

10.9

23.6

12.50

8.80

22.1

47.7

. 46

1.163

12.5

26.5

1..

u

22.3

47.4

47

NXII

N XIII a

1.369

13.7

27.9

13.00

9.80

24.2

49.2

49

1.369

13.7

27.9

l.i

?32

24.2

49.2

49

N XIV b

1.407

14.0

27.8

13.05

9.50

26.5

52.7

!o

g

1.429

14.0

28.5

13.20

9.50

27.1

55.0

49

a

1.431

14.6

30.4

12.85

10.20

23.2

48.4

48

i

1.431

14.9

29.6

13.40

10.30

25.3

50.2

50

e

1.437

12.6

28.7

13.25

9.60

24.1

54.1

44

k

1.445

13.2

28.4

13.30

9.50

26.0

55.8

47

1.430

13.9

28.9

1.35-^

25.4

52.7

48

NXVc

1.517

13.0

29.0

13.20

9.60

24.7

55.0

45

e

1.557

12.7

25.7

13.50

9,20

27.4

55.4

49

a

1.564

14.1

29.0

13.50

9.80

. 26.8

55.0

49

1.546

13.3

27.9

lA

.0=

26.3

55.1

48

N XVI a

1.619

14.7

31.3

13.80

10.50

25.4

54.2

47

g

1.632

13.8

27.6

13.70

9.50

28.8

57.6

50

e

1.636

13.2

28.2

13.80

9.60

27.3

58.2

47

1.629

13.9

29.0

1.^

.0'

27.2

56.7

48

N XVII e

1.710

13.4

29.5

13.80

9.70

27.2

59.8

.44

g

1.721

15.7

32.1

13.60

10.10

28.5

58.4

49

a

1.738

15.2

33.2

, 14.10

10.60

27.0

58.8

46

c

1.788

15.0

30.7

13.95

10.10

28.6

58.6

49

1.739

U.8

31.4

1.37-^

27.8

58.9

47

102

NAOKI SUGITA

TABLE 9— Continued

BRAIN WEIGHT

OBSERVED

CORRECTIONCOEFFICIENT

CORRECTED

PERCENTAGE OF CORTICAL

Area of cortex

Area of total section

W. D

in fresh brain

The

same on

slide

Area of corte.x:

Area of

total

section

AREA IN TOTAL SECTION

grams

mm.

mm .

m m .

mm.

7)1 m.

mm.

per cent

N XVIII c

1.825

15.0

32.3

14.45

10.30

29.6

63.7

47

a

1.833

19.0

39.2

13.95

11.20

29.5

61.0

49

1.829

17.0

35.8

1.32

29.6

62.4

48

NXIXb

1.962

16.6

36.6

14.60

11.20

28.3

62.3

44

a

1.981

15.3

32.9

13.95

10.30

28.1

60.5

47

1.972

16.0

34.8

1.33'

28.2

61. 4

46

NXXc

2.015

14.6

33.1

14.30

10.20

28.7

65.2

44

a

2.089

15.7

35.5

14.50

10.95

27.6

62.3

44

2.052

15.2

3^.3

1.36^

28.2

63.8

u

N XXI g

2.156

15.1

35.1

14.75 10.70

28.7

67.0

43

d

■2.187

15.3

34.0

15.05 10.70

30.3

67.4

45

« 

2.172

15.2

3J^.6

1.39-^

29.5

67.2

44

section may be calculated by the following formula, in which Ts denotes the average cortical thickness in the sagittal section.

L. F X T^X 1.20

(L. F and T^,, in millimeters)

The corresponding coefficient was found to be 1.22 in the Albino brains weighing more than 0.5 gram (table 4), but 1.20 for brains weighing more than 1.3 grams (Groups XIII-XX). The coefficients in the two forms may therefore be considered similar, that for the Albino being a trifle the larger.

If comparison is made between the absolute values of the cortical areas in the sagittal sections of the Norway and the Albino brains of like weight, no great difference appears (table 12). In the pair of Groups N XI and XI, the Norway is 10 per cent smaller in the area. This may be explained by the fact that the Norway brain weighing 1.16 grams is in a younger stage of cortical development, as compared with the Albino brain of like weight, the cortex of which is already provided with nearly all its nerve elements. But, in the pairs of Groups N XIII-XIII

GROWTH OF THE CEREBRAL CORTEX

103

TABLE 10 Giving for each individual and for each hrain weight group the number of nerve cells in 0.001 mm.^ of the cerebral cortex, in the lamina pyramidalis and in the lamina ganglionaris , and also the number of the ganglion cells only in the same volume of the lamina ganglionaris, counted at locality VII in the frontal section, as shown in fig. 2. Norway rat

BRAIN WEIGHT

CORRKCriOXCOEFFICIENT

XU.MBER OF CELLS IX .\ VOLU.MB 0.001 MM.-"

OF CORTEX,

GROUP

ir. D

in fresh brain

W.D

on slide

Lam. p.

•raniid.

Lam. ganglion.

Ganglion cells in lam. gangl.

Observed

Corrected

Observed

Corrected

Observed

Corrected

grams

mm.

mm.

N XI b

1.155

13.00

10.00

253

115

170

78

44

20

a

1.160

12.70

9.80

242

111

164

76

41

19

i

1 . 175

12.50

8.80

271

95

199

69

48

17

1 . 163

(1/1

34)'

255

107

178

74

44

19

NXII

N XIII a

1.369

13.00

9.80

225

96

164

70

45

19

1.369

{1/1.33)^

225

96

164

70

45

19

N XIV b

1.407

13.05

9.50

243

94

174

67

46

18

g

1.429

13.20

9.50

227

85

176

65

48

18

a

1.431

12.85

10.20

200

100

142

71

40

20

i

1.431

13.40

10.30

222

101

175

79

47

21

e

1.437

13.25

9.60

225

86

165

63

49

19

k

1.445

13.30

9.50

230

84

178

65

51

19

1430

il/l

35)^

225

92

168

68

47

19

NXVc

1.517

13.20

9.60

235

90

169

65

52

20

e

1.557

13.50

9.20

250

79

176

56

58

IS

a

1.564

13.50

9.80

208

79

166

63

55

21

1.546

{l/l

40)'

231

83

170

61

55

20

NXVIa

1.619

13.80

10.50

203

90

143

63

50

22

g

1.632

13.70

9.50

235

78

159

56

60

20

e

1.636

13.80

9.60

214

72

164

55

57

19

1.629

{1/1

40)^

217

80

155

58

56

20

N XVII e

1.710

13.80

9.70

213

74

155

54

58

20

g

1.721

13.60

10.10

182

75

147

60

54

22

a

1.738

14.10

10.60

190

81

131

56

54

23

c

1.788

13.95

10.10

192

73

142

54

53

20

1.739

{1/1. 37Y

194

76

lU

56

55

21

104

NAOKI SUGITA

TABLE 10— Continued

'

BRAINWEIGHT

CORRECTIONCOEFFICIENT

NUMBER OF CELLS IN A VOLUME OF CORTEX, 0.001 MM. 3

■ GROUP

\V. D

in fresh brain

W.D on slide

Lam. pyramid.

Lam. ganglion.

Ganglion cells in lam. gangl.

Observed

Corrected

Observed

Corrected

Observed

Corrected

N XVIII c

a

NXIX b

a

NXXc

a

NXXIg

d

grams

1.825 1.833

1.829

1.962 1.981 1.972

2.015 2.089 2.052

2.156

2.187 2.172

mm.

14.45 13.95

(1/1

14.60 13.95

(1/1

14.30 14.50

(1/1

14.75 15.05

(.1/1

?nm.

10.30 11.20

32)^

11.20 10.30

33y

10.20 10.95

36y

10.70 10.70

39y

200 147 174

164 176

170 ■

189 170

180

180 186

183

• 73

76

75

74 71 73

69

74

72

69 67 68

146

114

130

120 134

127

140 116

128

118 120

119

53 59 56

54

54 54

51 50

51

45 43

u

55 42

49

45

48 47

49 44

47

45 46

46

20

22

21

20 19

20

18 19 19

17

17

17

to N XX-XX the Norway shows a sHght excess in the area ; on the average 2 per cent.

In spite of the fact that an adult Norway brain has a thicker cortex (by about 6.7 per cent in the sagittal section) than the Albino brain of the same weight, yet between the two a smaller difference in the area of the cortex in the sagittal section is found, because of the shorter longitudinal diameter of the cerebrum (L. F) in the Norway (Sugita, '18).

0. The area of the cortex in the frontal section, pared with ihe Albino

Norway rat com

bust as in the case of the sagittal section, table 13 shows relations between the cortical area in the frontal section and the frontal diameter of the cerebrum iW. D). As a result, we see

that the relative value C/D or ^ ,.- i -, • , stands almost

' Cortical thickness

in a fixed ratio to the frontal diameter TF. D, that is, from 0.94

GROWTH OF THE CEREBRAL CORTEX

105

TABLE 11

Shotving relations between the cortical area in the sagittal section and the sagittal diameter of the cerebrum (L. F). Column E gives the relative lengths of the long side when the area is reduced to. a rectangle with the short side equal to the cortical thickness. These values have almost a fixed ratio to the sagittal diameter of the cerebrum (L. F) in each group, the average being 1.20. For the ex-planation see the text

A

B

C

D

E

P

G

' BRAIN WEIGHT GROUP

BRAIN WEIGHT

CORTICAL AREA IN

S.^GITTAL SECTION

CORTICAL

THICKNESS

IN SAGITTAL

SECTION

c

D

L.F

E F

grams

TO?«2

mm.

mm..

mm.

NXI

1.163

24.0

1.61

14.9

12.2

1.22

NXII

NXIII

1.369

27.5

1.73

15.9

13.1

1.21

NXIV

1.430

29.2

1.84

15.9

13.2

1.21

NXV

1.537

28.4

1.82

15.6

13.5

1.16

NXVI

1.629

30.5

1.88

16.2

13.6

1.19

NXVII

1.739

31.8

1.94

16.4

13.9

1.18

N XVIII

1.829

33.0

1.93

17.1

14.3

1.20

NXIX

1.972

33.8

1.97

17.2

14.6

1.18

NXX

2.052

33.8

1.92

17.6

14.7

1.17

NXXI

2.172

35.0

1.99

17.6

15.1

1.17

NXXII

N XXIII

2.345

35.7

1.86

19.2

15.5

1.24

Average (Groups N XI-N XXIII)

1.20

'

Average (Groun.s N XIIT-N XX^

1.19

to 1.00 or on the average 0.97 for Groups N XI-N XXI, so that the cortical area in the frontal section may be obtained by the following formula, in which T^ denotes the average cortical thickness in the frontal section:

W. D X T^ X 0.97 (W. D and T,-, in millimeters)

For Groups N XIII-N XX, the coefficient is 0.98 (table 13). The corresponding coefficient in the Albino, Groups XIII-XX, is about 0.93, as shown in table 5. Comparing the absolute values of the cortical area in the frontal sections in two forms of like brain weight group (Groups N XIII-N XX to Groups XIII-XX), we find that in the Norway it is on the average larger by about 10 per cent (table 12).

106

NAOKI SUGITA

TABLE 12

Com/parison of the Norway rat brain with the Albino rat brain of like weight in the areas of the cortex^ in the sagittal and the frontal sections and in the area of the total frontal section. The data were taken fram tables 1, 2, 8 and 9

BRAIN WEIGHT GROUP

BRAIX

WEIGHT

AREA OF CORTEX INSAGITTAL SECTIOX

AREA OF

CORTEX IN

FRONTAL

SECTION

AREA OF

TOTAL FRONTAL

SECTION

Albino

Norway

Albino

Norway

Albino

Norway

Albino

Norway

gram s

grams

mm.

TOm.2

7mn .2

mm.^

mm. 2

TO TO. 2

XI

1.171

1.163

26.6

24.0

21.7

22.3

45.7

47.4

XII

1.253

26.1

23.0

47.2

XIII

1.335

1.369

27.6

27.5

23.2

24.2

50.2

49.2

XIV

1.445

1.430

28.2

29.2

24.8

25.4

52.3

52.7

XV

1.554

1.542

28.7

28.4

24.3

26.3

54.0

55.1

XVI

1.656

1.629

29.2

30.5

24.3

27.2

54.9

56.7

XVII

1.726

1.739

31.1

31.8

24.6

27.8

56.4

58.9

XVIII

1.839

1.829

32.8

33.0

26.0

29.6

58.9

62.4

XIX

1.924

1.972

32.3

33.8

24.8

28.2

57.0

61. 4

XX

2.054

2.052

33.7

33.8

24.9

28.2

63.4

63.8

XXI

2.172

35.0

29.5

67.2

XXII

XXIII

2.345

35.7

Average for Groups XIII

XX

1.692

1.695

30.5

31.0

24.6

27.1

55.9

57.5

The total area of the frontal section is also slightly in favor of the Norway (table 12).

P. Percentage of the urea of the cortex to the lotal area of the frontal

section (one hemicerehrum) . Norway rat compared

with the Albino

As for the percentage of the cortical area to the total area of the section, a comparison between the two forms is interesting. In the Albino this percentage value increases from birth to a brain weighing 0.7 to 1.2 grams when it attains the value of about 48 per cent (table 2), but in the Norway the highest percentage is attained in brains weighing 1.1 to 1.8 grams. This indicates that the cortical organization is more retarded in the Norway, if the brain weight be taken as the basis of comparison. In a fully mature Norway brain (from Group N XX onwards,

GROWTH OF THE CEREBRAL CORTEX

107

TABLE 13 Showing relations between the cortical area in the frontal section and the frontal diameter of the cerebrum {W. D). Column E gives relative lengths of the long side ivhen the area is reduced to a rectangle toith the short side equal to the cortical thickness. These values have almost a fixed ratio to the frontal diameter of the cerebrum {W. D) in each group, the average being 0.97. For the detailed explanation see also the text. Norway rat

A

B

C

D

E

F

G

CORTICAL

CORTICAL

BRAIN WEIGHT

B BAIN

AREA IN

THICKNESS

C

ir D

E

GROUP

WEIGHT

FRONTAL SECTION

IN FRONT.\^L SECTION

D

F

grams

mm.

vim.

vim.

mm.

NXI

1.163

22.3

1.88

11.9

12.7

0.94

NXII

NXIII

1.369

24.2

1.96

12.3

13.0

0.95

NXIV

1.430

25.4

1.95

13.0

13.2

0.98

NXV

1.546

26.3

2.04

12.9

13.4

0.96

NXVI

1.629

27.2

2.08

13.1

13.7

0.96

N XVII

1.739

27.8

2.07

13.4

13.9

0.96

N XVIII

1.829

29.6

2.08

14.2

14.2

1.00

NXIX

1.972

28.2

2.00

14.1

14.3

0.99

NXX

2.052

28.2

1.96

14.4

14.4

1.00

NXXI

2.172

29.5

2.08

14.2

14.9

0.95

Average (Gro

ups N XI

N XXI) . . .

0.97

Average (Gro

ups N XIIT-N XX)

0.98

table 9) this percentage amounts to 44 per cent, which is equal to that seen in the mature Albino brain (Groups XVI to XIX, table 2), if we disregard one case of advanced age (Group XX).

Q. Number of cells in a unit volume of the cortex, compared with the Albino

Norway rat

Reviewing table 10 which gives separately the numbers of nerve cells in the unit volume of 0.001 mm.^ of the lamina pyramidalis and the lamina ganglionaris at a fixed locality m the frontal section of the cerebrum and counted by the same method used for the Albino rat and comparing these numbers with those in table 3 in part I, it is easily seen that, if the like brain weight groups of the two forms are paired, the number of cells in the unit volume of both layers is slightly lower in the Norway rat.

108

NAOKI SUGITA

These relations are shown in table 14. As for the number of the ganghon cells only in the lamina ganglionaris, it is always lower by 2 to 6 in the Norway and the highest figure (21) in the Norway is seen in Groups N XVII and N XVIII, while in the Albino the highest figure (25) is attained in Groups- XIII and XIV and again in Group XVII. In the Albino a temporary increase of cell number in the lamina ganglionaris was seen in Groups XIII and XIV, and in my Norway sections a similar phenomenon is indicated in Groups N XVII and N XVIII. Generally speaking, therefore, the cell densit}^ in the cerebral cortex, as far as represented by my observations, is slightly

600 ■i'in

X

•r^

.---'

--°

'•^

^o—

-o —

.^

■- -0^

-.

— .r

iLwr

tsn

/'

,wr

■^

.•

-~.y

350 300

^

^.=^

""'

^

-LV\

H'

200

_

rr

^:

^

100

"~"

—

—

—

— ~-r

M

50

1

do 11 12 1.3 14 d.5 1.6 L7

1.9 2.0 2.1 2.2 2.3 2.4

yns.

Chart 4 Showing the computed values for the cortical volume, the volume of the cerebrum, the cenn density in two unit volumes and the computed number of nerve cells in the entire cortex of the Norway rat, according to the brain weight. This chart is equivalent to, but not directly comparable with chart 2, which gives the similar data in the Al'bino in ratios of the values at birth. • •LWT', The computed volume of the cerebral cortex, based on table 15.

hWH' , The relative volume of the entire cerebrum, based on the data

presented in a former paper (Sugita, '18) and given also in table 15. X— — XN', The cell density in two unit volumes of the cortex. Graph based on the data

given as N in column D, table 16. -" — ^NLWT', The computed number of

nerve cells in the entire cortex, based on the figures given in column E, table 16. Mark X shows the phase in growth corresponding to that indicated by the same mark in chart 2, which shows the end of the second developmental phase in the Albino.

GROWTH OF THE CEREBRAL CORTEX

109

TABLE 14. Comparison of the Norway rat brain with the albino rat brain of lilie weight for the nuvibers of nerve cells in the lamina pijramidalis and in the lamina ganglionaris and the number of ganglion cells only in the lamina ganglionaris, in a unit volume of 0.001 mm.^, and also for N, which is the sum of the numbers in the lamina pyramidalis and in, the lamina ganglionaris. The data were taken from tables 3 and 10

NUMBER OF

CELL.S

IX .4 UNIT VOLUME

N,

OF

ORTEX

0.001

MM. 3

THE SUM OF

DRAIN WEIGHT

NUMBERS

DRAIN WEIGHT GROUP

Lam.

pyrani .

Lam .

gangl.

Ganglion

cells in lam.

gangl.

OF CELLS IN

L.iM. PYR.

AND IN

LAM. GANG.

Al

Nor

Al

Nor

Al

Nor

Al

Nor

Al

Nor

bino

way

bino

way

bino

way

bino

way

bino

way

grams

grams

XI

1.171

1.163

113

107

73

74

23

19

186

181

XII

1.253

103

68

23

171

XIII

1.335

1.369

99

96

77

70

25

19

176

166

XIV

1.445

1.430

94

92

71

68

25

19

165

160

XV

1.554

1.546

87

83

62

61

23

20

149

144

XVI

1.65G

1.629

84

80

60

58

24

20

144

138

XVII

1.726

1.739

83

76

63

56

25

21

146

132

XVIII

1.839

1.829

79

75

59

56

23

21

138

131

XIX

1.924

1.972

81

73

51

54

24

20

132

127

XX

2.054

2.052

80

72

51

51

20

19

131

123

XXI

2.172

68

44

17

112

Average for Groups

XIII-XX

1.Q92 1. 695

86

81

62

60

24

20

148

140

lower in the Norway rat, if the brain weight be selected as a standard of comparison.

/?. The computed volume of the entire cerebral cortex, compared with the Albino

Norumij rat

The computed volume of the cerebral cortex for the Norway may also be obtained and expressed in values comparable among themselves, by the use of the formula: L. F X W. D X T (where T denotes the mean thickness of the cortices in the sagittal and the frontal sections), as already explained in detail in part I (see p. 82). But for a comparison between the cortical volumes of the Norway and of the Albino brains, the direct comparison

THE JOURNAL OP COMPARATIVE NEUROLOGY, VOL. 29, NO. 2

110 NAOKI SUGITA

of the values obtained by the above fonnuhxs is not allowable, since, comparing the areas in the Albino among themselves, the fixed coefficients"' 1.21 and 0.93 were ehminated from the formula, as already stated, and similarly in the Norway the corresponding coefficients'^ 1.19 and 0.98 were also eliminated from the formula. In order to compare the areas in these two forms, the coefficients must be taken into consideration. As the product 1.19 X 0.98 is higher by 3.6 per cent than theproduct 1.21 X 0.93, the value of L. F X W.D X T for the Norway should be raised by 3.(3 per cent to be directly comparable with the \'alue of L. F X

1 1 Q V 98 IF. D X T for the Albino. The ratio =,','! r^L (= 1-03(3)

1.21 X 0.93 ^

being represented by C, the comparable value of the cortical

volume for the Norway may be obtained by the corrected formula

as follows:

L. F X W. D X T XC (C ^ 1.036)

Table 15 gives the computed cortical volume of the Norway brain, obtained according to the above corrected formula, and this is shown graphically in chart 4 (graph LWT').

As the available data in the Norway do not extend to the earlier ages, I could not determine the early increase in the cortical volume of the Norway, but our data show that the cortical volume is increasing somewhat more rapidly during the period when the brain weight is increasing from 1.16 to 1.54 grams and after that it increases more slowly but steadily as the entire cerebral volume increases, as shown in table 15 and in chart 4 (graph LWH'). In the Albino, as has been shown, the cortical volume increases relatively rapidly until the brain attains 1.17 grams in weight, a phase which probably corresponds to the phase in the Norway of 1.43 grams in brain weight.

To compare the cortical volume in the Norway rat with that of the Albino, I have paired, in table 15, the Norway data {L. F XW. D X T X C] directly with the corresponding Albino

For a proper (;onii)arisoii, the eoeflficieuts here used are those for the same brain weight groups compared in both forms, l)eing respectively the averages for Groups XIII to XX and for Groups N XIII to N XX, taken from tables 4, 5, 11 and 13.

GROWTH OF THE CEREBRAL CORTEX

111

TABLE 15

Showing the computed volume for the entire cerebral cortex of the N'orway rat hraiii, calculated by the formula: L.F X W. D X T X C for each brain iveight group, C being a fixed coefficient used to convert the computed volume of the Norway cortex so as to make it comparable with that of the Albino {C = 1.036). The computed volume of the cerebrum is quoted from my previous presentation (Sugita, '18). These values are paired ivith the corresponding values for the cortical volume of the Albino and the ratios between them, calculated

NORWAY RATS

ALBINO RATS

A

B

C

D

E

F

G

H

I

Brain weight group

Brain

wciglit

Computed

volume

of

cerelirum

L.G X W.DXHt.

L.F

in fre.sli

brain

\V. D

in fresh

brain

average cortical

thickness

L.FX W. D XT

XC

Computed

volume

of corte\

Corresponding computed volume of the Albino cortex, of the same group number

Ratio

of cortical

volume

of the

Norwav

to that of

the

Albino

grams

)H tn .3

mm .

)// m .

m m .

mm .^

7)1 m.^

NXI

1.163

156

12.2

12.7

1.75

281.00

288.93

0.973

NXII

304.51

NXIII

1.369

182

13.1

13.0

1.85

326.51

314.03

1.040

NXIV

1.430

185

13.2

13.2

1.90

343.09

329.71

1.040

NXV

1.537

194

13.5

13.4

1.93

361.83

345.86

1.046

NXVI

1.629

203

13.6

13.7

1.98

382.32

359.30

1.064

NXVII

1.739

218

13.9

13.9

2.01

402.47

365.08

1.102

N XVIII

1.829

226

14.3

14.2

2.01

423.00

397.96

1.063

NXIX

1.972

241

14.6

14.3

1.99

430.57

390.39

1.103

NXX

2.052

249

14.7

14.4

1.94

425.59

393.15

1.0S3

NXXI

2.172

264

15.1

14.9

2.04

475.66

Average

(Groups

N XIII

N XX) .

386.92

361.94

1.069

1 T, here entered, is the mean value of T, and Tp, previously given in tables 11 and 13 and is not the general average thickness of the corte.x of the sagittal, frontal and horizontal sections formerly presented in my fourth paper in this series (Sugita, '18 a).

data (L. F X W. D X T) according to the brain weight groups, quoted from part I. In table 15 the ratios show the volume of the cortex in the Norway to be greater (1.040 to 1.103) in all the comparisons for brain weights above Groups XIII (brain weight 1.87 grams). The average value is about 1.07. In Group XI (brain weight 1.17 grams), the ratio for the Norway is less than 1. At this weight the Norway brain is regarded as less mature than

112 NAOKI SUGITA

the corresponding Albino brain. The ratio tends to increase as the brain weight increases, showing roughly the relative growth in the Norway cortex.

Since, as has been shown (Sugita, '18 a), the cortex in the mature Norw^ay is about 8 per cent thicker (average of the sagittal and frontal sections) than in the Albino, and since this value enters as T into the formula under discussion, this would tend to give a greater \'olume of the cortex in the Norway than in the Albino. The mean value found for the ratio of the cortical volume — 1.07 — is about that to be expected, in view of the relatively smaller value of L. F in the Norway.

>S. Computed number of nerve cells in the entire cortex. Norway rat compared with the Albino

As described in part I, the computed number of nerve cells in the entire cerebral cortex may be obtained by the following formula :^

NXL.FX W. D X T XC (L.F, ]V. D and T, in miUimeters) where L. F X W. D X T X C is the computed volume of the Norway cortex made comparable directly with the corresponding volume for the Albino, as explained in the foregoing chapter, and A^ is the cell density, represented by the sum of the numbers of cells in a unit volume in the lamina pjTamidalis and in a unit volume in the lamina ganglionaris (two unit volumes altogether), given separately in table 10 and combined in table 16.

Table 16 gives the computed value of the cell number in the entire cerebral cortex for each brain weight group of the Norway rats (column E), calculated by the use of the above formula, and also in the corresponding case of the Albino (column G).

On examining table 16, column E, w^e find the computed number of nerve cells in the cortex to be nearly completed in a brain weighing 1.37 grams (Group N XIII), while in the Albino this condition was reached in a brain weighing 1.17 grams (Group XI). The value of the completed cell number is indicated in

The formula for the total number of nerve cells in the Norway cortex is like that for the Albino cortex with the addition of the factor C (footnote 4) .

GROWTH OP THE CEREBRAL CORTEX

113

TABLE 16

Giving the computed number of nerve cells in the entire cerebral cortex of the Norivay rat brain, obtained on the basis of the m.easurements given in this series of studies. These values are made to be comparable ivith the corresponding values of the computed number of nerve cells in the cortex of the albino rat brains of like brain weight groups

NORW.W R.\TS

ALBINO RATS

A

B

C

D

E

F

G

Brain weight group

Brain weight

Computed

volume of

cortex

L.FX n'. D

XT XC

Sum of numbers of

cells in lam. pyr.

and lam. gang, in two

unit volumes, N

Computed

number of cells

in entire

cortex,!

X XL.F

X It'. DXT

x^'x'iTo

Ratio of number of

cells in the Norway

to that in the Albino

Corresponding

computed number of cells

in the

Albino, of the

same group

number

NXI

NXII

NXIII

NXIV

NXV

NXVI

N XVII

N XVIII

NXIX

NXX

NXXI

grams

1.163

1.369 1.430 1.537 1.629 1.739 1.829 1.972 2.052 2.172

m m .3

281.00

326.51 343.09 361.83 382.32 402.47 423.00 430.57 425.59 475.66

181

166 160 144 138 132 131 127 123 112

508.6

542.0 548.9 521.0 527.6 531.3 554.1 546.8 523.5 532.7

0.946

0.981 1.009 1.011 1.020 0.997 1.009 1.061 1.016

537.4 520.7 552.7 544.0 515.3 517.4 533.0 549.2 515.3 515.0

Average (Groups N XIII-N XX)

536.9

1.013

530.2

1 As remarked in a note to table 7, the number given in this column corresponds to 1/100 of N X L. F X W. D X T,or 1/50,000 of the actual number of cells contained in the computed volume of the cortex.

the Norway by about 537 (the average of Groups N XIIIN XX) or about 1 per cent more than that of the Albino, which has been indicated by about 530 (the average of Groups XIIIXX, see table 7), so that the number of nerve cells in the entire cortex of the mature Norway and of the Albino rats may be regarded as practically the same, as suggested by Donaldson (Donaldson and Hatai, '11).

114 NAOKI SUGITA

IX. CONCLUSIONS

Putting together the foregoing observations, we come to the conclusion that in the case of the Norway rat brain the entire volume of the cerebral cortex is actively increasing up to a brain weight of something more than 1.43 grams (Group N XIV) and that the number of nerve cells in the cortex is completed in a brain weighing something less than 1.43 grams (Group N XIV) (chart 4). After this, the increase in cortical volume keeps pace with the enlargement of the entire cerebrum, showing that the cortical mass and the remainder of the cerebrum are growing at the same rate. So, the end of the short period during which the brain has attained 1.37 to 1.54 grams in weight (Groups N XIII to N XV) marks an epoch in the development of the cerebral cortex of the Norway rat, at which the structural completion of the cortex has been acquired and the full preparation for the functional education has been established. This period corresponds approximately to the age of twenty days.

In the Albino, the same degree of development is reached when the brain attains a weight of 1.17 grams or is twenty days old. As I suggested in an earlier paper (Sugita, '18 a), a Norway brain corresponds in the development of the cortex to an Albino brain weighing about 18 per cent less. This assumption has held true in the present examinations of the cortical volume and cell number, because an Albino brain weighing 1.17 grams just corresponds to a Norway brain weighing 1.43 grams.

The number of cells in the Norway cortex has been shown to be but slightly (1 per cent) different from that in the Albino rat cortex and may be regarded as the same in both forms. This fact justifies at the same time a conclusion reached by Donaldson in his former comparison of the Norway with the Albino rats, that the greater weight of the brain in the Norway rat, compared with the Albino of the same body weight or of the same age, is probably due to an enlargement of the constituent neurons rather than to an increase in their number (Donaldson and Hatai, '11). The results of my study regarding the cell size in the cortex in these two forms will be discussed in a forthcoming paper and will support the statement just made.

GROWTH OF THE CEREBRAL CORTEX 115

X. SUMMARY

1. On the sagittal and the frontal sections from 28 Norway rats, whose brain weights fall between 1.1 and 2.4 grams and which were formerly used for the investigation on the cortical thickness (Sugita, '18 a), the area of the cortex was measured and the number of nerve cells, in a unit volume of 0.001 mm.^ at a fixed locality of the cortex, was counted. These values were all later corrected to the corresponding values in the fresh condition of the material, using the correction- coefficients devised for this purpose. These results have been grouped and averaged according to the brain weight and then compared with the corresponding data in the Albino, which were presented in part I of this paper.

2. The actual area of the cortex in the sagittal section may be obtained by the formula: L. F X T^X 1.20 (L. F and T^, in millimeters), where L. F is the longitudinal diameter of the cerebrum, T^ is the thickness of the cortex in the sagittal section and 1.20 is a constant coefficient which was empirically determined (table 11, column G).

3. The actual area of the cortex in the frontal section may be obtained, though less precisely, by the formula: W. D xT^ X 0.97 {W. D and T^ in millimeters), where W. D is the frontal diameter of the cerebrum, T^ is the thickness of the cortex in the frontal section and 0.97 is a constant coefficient which was determined empirically (table 12, column G).

4. The percentage of the cortical area to the area of the whole frontal section is highest (48 per cent) in brains weighing 1.1 to 1.8 grams. In a fully mature brain it has fallen to 44 per cent.

5. The computed value for the volume of the entire cortex, indicated by the formula: L. F X W. D X T X C (L. F, W. D and T, in millimeters), where L. F is the longitudinal diameter, W. D is the frontal diameter of the cerebrum, T is the average thickness of the cortex in the two sections and C a theoretically determined coefficient necessary to make the values directly comparable with the corresponding values for the albino rat, shows that the cortex is increasing relatively rapidly in the

116 NAOKI SUGITA

Norway brains weighing less than 1.43 grams. After that stage its increase nearly keeps pace with the increase in the volume of the entire cerebrum.

6. In Norway brains weighing from 1.1 to 2.2 grams, the cell density or the number of nerve cells in a unit volume of the lamina pyramidalis and the lamina ganglionaris, in a fixed locality of the cortex, decreases slowly but steadily as the brain weight advances. It has proved sHghtly less than that in the Albino (compare table 16, column D, with table 7, column C). In the lamina ganglionaris the number of ganglion cells onl}^ in a unit volume is at its highest in the brains weighing 1.7-1.8 grams (table 14).

7. The value for the computed number of nerve cells in the entire Norway cortex, indicated by the formula: A*^ X L. F X Wl D XT XC (L. F, W. D and T, in millimeters), where A^ is the number of cells in two unit volumes and L.F x W. D X T X C is the computed volume of the cortex, shows that it is almost completed in a brain weighing something more than .37 grams.

8. Comparisons in respect of the above characters between the Norway and the Albino brains of the like weight show that, in the cortical areas in the sagittal and the frontal sections and in the volume of the entire cortex, the Norway rat surpasses the albino rat, but the number of cells as computed for the entire cortex may be regarded as the same in both forms. We conclude therefore that the difference in absolute brain weight between the two forms is not correlated with a difference in the number of nerve cells in the cerebral cortex. In a Norway brain weighing 1.4 to 1.5 grams, which corresponds to an Albino brain weighing 1.17 grams and is about twenty days in age, the elemental organization of the cerebral cortex in the Norway rat is considered to be almost completed.

GROWTH OF THE CEREBRAL CORTEX 117

LITERATURE CITED

Allen, Ezra 1912 The cessation of mitosis in the central nervous system of the albino rat. Jour. Comp. Neur., vol. 22, no. 6.

Donaldson, H. H. 19 8 A comparison of the albino rat with man in respect to the growth of the brain and of the spinal cord. Jour. Comp. Neur. and Psychol., vol. 18, pp. 345-392.

1915 The Rat. Memoirs of The Wistar Institute of Anatomy and Biology, no. 6.

Donaldson, H. H. and Hatai, S. 1911 A comparison of the Norway rat with the albino rat in respect to body length, brain weight, spinal cord weight and the percentage of water in both the brain and the spinal cord. Jour. Comp. Neur., vol. 21, pp. 417-458.

Stjgita, Naoki 1917 Comparative studies on the growth of the cerebral cortex. I. On the changes in the size and shape of the cerebrum during the postnatal growth of the brain. Albino rat. Jour. Comp. Neur., vol. 28, no. 3.

1917 a Comparative studies on the growth of the cerebral cortex. II. On the increase in the thickness of the cerebral cortex during the postnatal growth of the brain. Albino rat. Jour. Comp. Neur., vol. 28, no. 3.

1918 Comparative studies on the growth of the cerebral cortex. III. On the size and shape of the cerebrum in the Norway rat (Mus norvegicus) and a comparison of these with the corresponding characters in the Albino rat. Jour. Comp. Neur., vol. 29, no. 1.

1918 a Comparative studies on the growth of the cerebral cortex. IV. On the thickness of the cerebral cortex of the Norway rat (Mus norvegicus) and a comparison of the same with the cortical thickness in the Albino. Jour. Comp. Neur., vol. 29, no. 1.

AUTHOR S ABSTRACT OP THIS PAPER ISSUED BY THE BIBLIOGRAPHIC SERVICE, MARCH 2.

COMPARATIVE STUDIES ON THE GROWTH OF THE CEREBRAL CORTEX

VI. PART I. ON THE INCREASE IN SIZE AND ON THE DEVELOPMENTAL CHANGES OF SOME NERVE CELLS IN THE CEREBRAL CORTEX OF THE ALBINO RAT DURING THE GROWTH OF THE BRAIN

VI. PART II. ON THE INCREASE IN SIZE OF SOME NERVE CELLS IN THE CEREBRAL CORTEX OF THE NORWAY RAT (mUS NORVEGICUS), COMPARED WITH THE CORRESPONDING CHANGES IN THE ALBINO RAT

NAOKI SUGITA

From the Wislar Institute of Anatomy and Biology

WITH SIX FIGURES AND FOUR CHARTS

PART I

I. PRELIMINARY STUDIES

As a preliminary to the study of cell size, I made a comparison of effects of several fixatives and imbedding media on the size and shape of the cortical nerve cells in a small number of albino rats. These studies were made after considering the results of King ('10) and Allen ('16), both of whom were endeavoring to find methods which caused the minimum alteration in the nerve cells.

For this comparison, ten kinds of preparations were made from albino rat brains of like age: thus, as the fixative, (1) Bouin's fluid, (2) 4 per cent formaldehyde, (3) 95 per cent alcohol, (4) Muller's or Orth's fluid, and (5) Ohlmacher's fluid were successively^ tried, and each sample was inbedded in (A) parafine and in (B) celloidin.

119

120 NAOKI SUGITA

Formaldehyde fixation and paraffine imbedding (2A) causes considerable shrunkage of nuclei and cell bodies, especially in young brains, but material so prepared takes any aniline dye excellently well (fig. l,b). Fixation in Miiller's or Ortti's fluid and paraffine imbedding (4A) causes also shrinkage and deformation of the cell bodies and nuclei, the contours of which become zigzag. Formaldehyde fixation and celloidin imbedding (2B) give good figures of cell bodies, which stain excellently with any aniline dye. The shrinkage of cells and nuclei which was seen after paraffine imbedding of the material similarly fixed (2A) is no longer observed. But the size of cell bodies and nuclei seems to have suffered some diminution. Miiller or Orth fixation and celloidin imbedding (4B) causes considerable deformation of the contours of the cells and nuclei, which is probably an affect of the potassium bichromate.

In material fixed in 95 per cent alcohol, the brain is subject to much shrinkage, and consequently the cell size and cortical thickness diminish also, though, after paraffine imbedding (3A), the contours of cells and nuclei are preserved pretty well (fig. 1,a). Alcohol fixation only or alcohol fixation and celloidin imbedding (3B) is ideal for the study of the cytoplasmic strticture as originally emphasized by Nissl. The cell bodies stain very well with aniline dyes, but the section shrinks so that the individual cells must have been more or less reduced in size. Fixation in Ohlmacher's fluid and paraffine imbedding (5A) or celloidin imbedding (5B) proved to be most excellent for cell study, as pointed out by King ('10), but it is followed after fixation by a considerable reduction in the volume of the total brain and some change in shape.

After a number of tests, I decided to use as the fixative Bouin's fluid, which is composed of:

cc.

Picric acid, saturated aqueous solution 75

40 per cent formaldehyde (formalin) 25

Glacial acetic acid 5

Fixed in this fluid the total weight or ^'olume of the brain suffers no significant change after complete fixation and preserves its original shape quite well, though a slight shrinkage occurs,

GROWTH OF THE CEREBRAL CORTEX

121

no matter what the age of the brain is. It takes only a couple of hours to complete fixation in this fluid, if the fluid is kept in the oven at 37C., but, as a matter of convenience, I left each brain in 20 cc. of this fluid for 24 hours at the room temperature. By this treatment the form of the cells was well preserved, even after imbedding in paraffine (lA) (figs. 3 and 4).

Comparing this w^ith the material which was fixed in the same fluid but imbedded in celloidin (IB), the contours of cell bodies were, in the former, somewhat indistinct and the size of the nuclei somewhat larger (fig. 1, c). But after paraffine imbedding the nuclei have yet good contours which are not zigzag and the

Fig. 1 Showing pj'ramids from the lamina pyramidalis at a fixed locality (locality VII) of the cerebral cortex of Albino brains weighing 1.3 to 1.5 grams. Magnification of about 950 diameters, measured directly on the slide, a = from a brain imbedded in paraffine after fixation in 95 per cent alcohol, b = from a brain imbedded in ])araffine after fixation in 4 per cent formaldehyde, c = from a brain imbedded in celloidin after fixation in Bouin's fluid.

so-called Nissl bodies are also well stained. Since paraffine was used exclusively for the imbedding medium, Bouin's fluid proved to be the best fixative for the albino rat brain, when it is required to follow the growth changes of the cortex by the measurements of the cells of the cortex.

Figure 1 shows a comparison of the effects of several fixatives on the shape and contours of the cell bodies and the nuclei when applied to albino rat brains of like age. The examples are all from Albino brains weighing 1.3 to 1.5 grams and represent pyramids in the lamina pyramidalis taken near the locality VII in frontal sections, being comparable with VII in figure 2, a and h.

122

NAOKI SUGITA

II. MATERIAL

For the present study on cell size in the cerebral cortex, the frontal and horizontal sections of the Albino brains which were used earlier for studies on the cortical thickness, cortical areas, and cell density (Sugita, '17 a, '18 b) were alone taken. No locahty in the sagittal sections was examined. These sections were from 128 individuals, sexes combined. The data for these 128 rats appear in tables 1 and 2 in a previous paper (Sugita, '17 a) and it is not thought necessary to repeat the tables here. This study was begun in January, 1916, and carried on with interruptions till Fel)ruary, 1917, at The Wistar Institute of Anatomy and Biology.

/^f

a

Fig. 2 Showing on tlie brain surface the localities at which the sizes of the pyramids and the ganglion cells were measured. FF' indicates the level from which the frontal section was taken and HH' indicates the level from which the horizontal section was taken. VII = locality \TI;X = locality X. a = the dorsal view of an Albino brain weighing 1.5 grams. Enlarged l.S diameters, b = the lateral view of the same.

III. TECHNIQUE

The nerve cells have been measured at fixed localities in the sections; that is, in the frontal sections at locality VII (fig. 4, Sugita, '17 a) and in the horizontal sections at locality X (fig. 6, Sugita, '17 a). For convenience, these locahties are here shown on two corresponding figures (fig. 2, a and b). From the lamina pyramidalis and the lamina ganglionaris at each of these localities, ten of the largest cells were selected and measured. The cells in the other layers were not systematically investigated,

GROWTH OF THE CEREBRAL CORTEX 123

but in several stages of growth, a few were measured, in order to be able to make some comparisons.

The study of the cells under the microscope was made with a Zeiss Comp. Ocular no. (3 with a micrometer, combined with the objective 2 mm., oil immersion. Each division in the micrometer scale was equal to two micra. The measurement of the cell size was executed in the following way : the transverse diameter of the cell body (the greatest width of the cell body) was measured on a line, parallel to the base line, which crossed about the middle of the nucleus. For the longitudinal diameter the measurement was made \'ertical to the trans\'erse diameter from the base of the cell body to the beginning of the apical dendrite. This last limit was assumed to be at the point where the Nissl bodies are no more to be seen and the side lines of the apical dendrite begin to run nearly parallel to each other. Sometimes this upper limit was very hard to determine, especially in fully grown cells, because of the irregularity of the cell outline and the relatively slow transition from cell bod}- to the apical dendrite. In these latter cases, the upper limit was somewhat arbitrarily fixed, but this procedure has apparently been without much effect on the results.

The measurements of the ten largest cells of the same kind from within the fixed locality in the same individual were then averaged for each diameter and recorded on cards without any correction. The average measurements from the frontal section and the horizontal section are denoted in the records by the letters F and H, respectively. The individual averages for each series of ten cells in each section have all been tabulated and the respective averages for the brain-weight groups found. The values for the individuals in each brain-weight group are so well correlated with their respective indi\ddual brain weights that it has seemed necessary to publish only the averages for the successive brain-weight groups. Table 1 contains the cell measurements on the frontal section averaged for each brainvk^eight group. The results of the measurements on the horizontal sections, which were taken from the other individuals,

124 NAOKI SUGITA

are given in table 2, and here also only the averages for the brain-weight groups are given. ^

The maximal diameters of the nuclei of the same cells were measured in the two directions in which the cell measurements were made. The nuclei have sharp contours, so that it was always easy to find the border points of the diameters. The results of the nuclear measurements ha\'e been treated in the same manner as the cell-body measurements and the average values are recorded also in the same way — ^without any correction — in tables 1 and 2.

In table 3 the final average diameters of the cell bodies and their nuclei for each brain-weight group are given for each section. These final average values were obtained by multiplying the values of the transverse and longitudinal diameters together and by extracting the square root of the product, thus assuming the cell- and nucleus-figures to form a plane instead of a solid body. By this treatment, the results for the nucleus do not differ much from those which would be obtained by using a planimeter, because the nucleus has a nearly spherical or ellipsoidal form. The cell body, on the contrary, appears as a somewhat irregular cone or pyramid in the outline. Nevertheless, its relative volume may be denoted by a^fe, or its area by ah, in which a is the transverse and h the longitudinal diameter. Accordingly, the relative values of the average diameter may be represented by 's/ab, but these values should not be compared directly with the average diameter of the nucleus, because the forms of the cell body and of the nucleus are quite different. The size of cell bodies and their nuclei was assumed to have shrunken in the same proportion as the total brain volume during the procedure of fixation, imbedding and mounting and the values observed were therefore corrected for the fresh condition of the material by the use of the correction-coefficient which was formerly used for the correction of the cortical thickness or other measurements made on the same section. The cell bodies and nuclei were assumed to have shrunken similarly in transverse and

^ The detailed data for tables 1 and 2 and also for tables 6 and 7 have all been tabulated and are on file at The Wistar Institute of Anatomy and Biology.

GEOWTH OF THE CEREBRAL CORTEX

125

TABLE I Giving the average uibcorrecled diameters of the nerve cells and their nuclei in the lamina pyramidalis and the lamina ganglionaris measured at the fixed locality {locality VII) on the frontal sections of the albino rat brain. The data are given for each brain iveight group only

BRAIN WEIGHT GROUP

I

II (B)

III

IV

V

VI

VII

VIII

IX

X

XI

XII

XIII

XIV

XV

XVI

XVII

XVIII

XIX

XX

NO. OF

BRAIN

TASKS

WEIGHT

grams

3

0.161

5

0.251

5

0.358

6

0.432

9

0.542

3

0.639

2

0.750

6

0.841

3

0.964

3

1.040

4

1.171

2

1.253

5

1.335

3

1.445

5

1 554

4

1.656

4

1.726

3

1.839

1

1.924

2

2.054

LAMINA PYRAMIDALIS

Cell body diameter

Transv. Longit.

7.5 10.3 11.9 14.1 14.4 15.0 15.2 16.5 16.9 16.6 16.8 16.2 16.0 15.4 15 5 15.0 15.7 14.7 15.6 15.2

M

10.7

13.0

15.5

17

17

17

18.

19.

20.2

20.1

20.6

20.7

20.7

20 4

20.0

19.6

19.9

19.4

19.9

19.5

Nucleus diameter

Transv. Longit.

6.6 9.2 10.7 12.4 12.4 12.9 13.5 14.0 15.7 14.8 14.7 14.6 14.6 14.3 14.2 13.8 14 3 13.6 14.0 13.5

7.6 10.3 12.4 13.5 13.4 13.9 14.2 14.8 16.4 15.3 16.1 15.4 15.2 15.1 14.8 14.7 15.2 14.5 14.3 14.3

LAMINA GANGLIONARIS

Cell body diameter

Nucleus diameter

Transv.

Longit.

Transv.

Longit.

M

M

A*

M

10.1

14.1

8.7

10.5

14.4

18.2

12.0

13.6

16.1

20.6

13.5

15.0

18.4

23.3

15.5

ir.i

19.5

23.4

16.2

ir.4

19.4

23.7

16.2

17.2

20.2

25.7

16.1

16.9

20.8

26.7

17.4

18.3

21.4

28.6

19.1

19.6

21.0

27.7

17.8

18.6

21.5

28.6

18.2

19.4

21.1'

27.7

18.0

18.6

20.4'

26.8

17.8

18.4

20.1'

27.0

17.5

18.3

21 2

27.4

18.0

18.6

21.7

29.1

18.1

19.4

22.0

28.0

18.7

19.5

22.3

28.5

18.4

19.0

22.7

29.3

18.8

19.4

23.2

31.4

19.3

20.2

' The uncorrected measurements of the cell body and the nucleus of the ganglion cells in these groups (Groups XII-XIV) show a slight decrease, while in the corrected measurements (see table 3) no diminution in cell size has occurred in this stage. This slight decrease in size on the slide is probably due to some chemical changes which takes place in cytoplasm during this phase of development. The same phenomenon is to be seen also in the ganglion cells measured on the horizontal section, given in table 2, in Groups XII-XVI.

longitudinal diameters and in the same proportion as the width of the brain has shrmiken. As in the other measurements (Sugita, '17 a, '18 a, '18 b), the correction-coefficient was

based on

W. D in fresh brain W. D. on the slide

for the frontal section and on

THE JOURN.\L OF COMP.VRATtVE NEUROLOGY, VOL. 29. NO. 2

126

NAOKI SUGITA

TABLE 2

Giving the average uncorrected diameters of the nerve cells and their nuclei in the lamina pyramidalis and the lamina ganglionaris measured at the fixed locality {locality X) on the horizontal sections of the albino rat brain. The data are given for each brain weight group only

NO. OF

CASES

BRAIN WEIGHT

LAMINA PYRAMIDALIS

LAMINA GANGLIONARIS

BRAIN WEIGHT GROUP

Cell body diameter

Nucleus diameter

Cell body diameter

Nucleus diameter

Transv.

Longit.

Transv.

Longit.

Transv.

Longit.

Transv.

Longit.

grams

M

M

M

fJ

M

M

M

M

11(B)

2

0.292

9.9

12.7

8.5

9.8

15.4

19.3

13.0

14.2

III

3

0.317

10.6

13.8

9.4

10.9

14.6

19.0

12.7

14.4

IV

3

0.419

13.0

14.0

10.2

12.9

16.0

21.4

14.2

16.3

V

5

0.546

13.9

16.5

12.5

13.5

18.7

23.5

16.0

17.5

VI

2

0.631

15.6

18.1

13.8

15.2

19.7

23.7

17.2

18.3

VII

2

0.761

15.6

18.5

14 3

15.7

19.4

24.9

17.6

19.0

VIII

4

0.848

15.5

19.1

14.4

15.8

20.1

26.3

18.1

19.3

IX

2

939

15.9

19.8

14.8

16.0

20.9

28.1

18.8

19.6

X

.3

1.054

16.1

20.6

14.9

15.7

20.7

28.5

18.8

19.8

XI

1

1.121

16.5

21.2

15.6

16.6

20.8

28.8

19.1

19.9

XII

3

1.240

16.0

20.5

14.7

15.9

19.51

27.8

17.6

19.2

XIII

3

1.351

15.9

20.9

14.6

15.5

20.31

29.1

17.6

19.0

XIV

2

1.455

15.1

20.1

13.9

14.9

20.7

28.4

18.1

19.1

XV

2

1.566

15.3

20.8

14.0

15.1

20.7

29.5

18.2

19.4

XVI

4

1.678

15.2

19.9

14.0

15.0

20.4

27.9

17.8

19.3

XVII

2

1.730

15.3

20.3

14.1

15.1

20.8

29.6

18.2

19.5

XVIII

2

1.823

15.5

20.5

14.3

15.1

21.1

29.9

18.4

19.6

XX

1

2.004

14.6

19.3

13.5

14.0

21.5

31.0

18.4

19.6

1 See note on table 1.

W. B in fresh brain

for the horizontal section, and apphed di

W. B on the sKde rectly to the final average diameters for the cell bodies and the nuclei. The corrected results, with the average correctioncoefficient for each brain-weight group, taken from previous papers (Sugita, '17 a, '18 b), are tabulated in table 3, accompanied with the averages of all the diameters in both sections for each brain-weight group.

GROWTH OF THE CEREBRAL CORTEX

127

TABLE 3 Giving the corrected final average diameters of the nerve cells and their nuclei of the lamina pyramidalis and the lamina ganglionaris measured on the frontal and the horizontal sections of the albino rat brain. The average values of the two for each brain iveight group are also given. The correction-coefficient for each brain weight group was taken from previous papers (Sugita, '17 a, '18 b). F = the frontal sectio7i. H = the horizontal section.

LAMINA PYRA.MIDALIS

L.\MINA GANGLIONARIS

BRAIN WEIGHT

BRAINWEIGHT

CORRECTIONCOEFFICIENT

OROUP

Cell body diameter

Nuc'eus diameter

Cell body diameter

Nucleus diameter

grams

M

M

M

i"

FI

0.161

1.14

10.3 •

8.1

13.6

10.9

HI

—

—

• —

—

—

—

0.161

10.3

8.1

13.6

10.9

FII

0.251

1.16

13.5

11.2

18.8

14.8

HII

0.292

1.10

12.3

10.0

18.9

15.0

(Birth)

0.272

12.9

10.6

18.9

14-9

Fill

0.358

1.13

15.4

13.0

20.6

16.0

HIII

0.317

1 21

14.6

12.2

20.1

16.3

0.338

15.0

12.6

20.4

16.2

FIV

0.432

1.10

17.2

14.2

22.8

17.9

HIV

0.419

1.30

17.5

14.8

24.0

19.6

0.426

17.4

14-5

23.4

18.8

FV

0.542

1.13

17.9

14.6

24.2

19.0

H V

0.546

1.22

18.5

15.9

25.6

20.4

0.5U

18.2

15.3

24.9

19.7

F VI

0.639

1.19

19.4

16.0

25.4

19.9

H VI

0.631

1 24

20.4

18.0

26.8

21.9

0.635

19.9

17.0

26.1

20.9

F VII

0.750

1.24

21.0

17.2

28.2

20.5

HVII

0.761

1.27

21.6

19.0

28.0

23.2

0.756

21.3

18.1

28.1

21.9

FVIII

0.841

1.20

21.5

17.3

28.3

21.4

H VIII

0.848

1.38

23.7

20.8

31.8

25.8

0.845

22.6

19.1

30.1

23.6

FIX

0.964

1.21

22.4

19.4

29.9

23.4

HIX

0.939

1.31

23.2

20.2

31.7

25.2

(10 days)

0.952

22.8

19.8

30.8

24.3

128

NAOKl SUGITA

TABLE 3— Continued

LAMINA PYRA.MIDALIS

LAMINA GANGLIONARI8

BRAIN- WEIGHT

BRAINWEIGHT

CORRECTIONCOEFFICIENT

GROUT

Cell body diameter

Nucleus diameter

Cell body diameter

Nucleus diameter

grams

At

M

M

M

FX

1 040

1.23

22.5

18.6

29.6

22.4

HX

1.054

1.36

24.8

20.8

33.0

26.3

1.047

23.7

19.7

31.3

24-4

FXI

1.171

1.26

23.4

19.4

31.4

23.8

HXI

1.121

1.26

23.7

20.4

31.0

24.6

(20 days)

1.146

•

23.6

19.9

31.2

24.2

FXII

1 253

1.31

24.0

19.6

31.6

24.0

HXII

1.240

1.36

24.6

20.0

31.7

25.9

1.247

24.3

20.3

31.7

24.5

FXIII

1.335

1.29

23.4

19.2

30.2

23.4

HXIII

1.351

1.34

24.4

20.2

32.6

24.5

1.343

23.9

19.7

31.4

24.0

FXIV

1.445

1.34

23.8

19.7

31.2

24.0

HXIV

1.455

1.31

22.8

18.9

31.7

24.4

1.450

23.3

19.3

31.5

24.2

FXV

1.554

1.30

22.9

18.9

31.4

23.8

HXV

1.566

1.28

22.9

18.6

31.6

24.1

1.560

22.9

18.8

31.5

24.0

FXVI

1.656

1.33

22.9

19.0

33.4

24.8

H XVI

1.678

1.32

23.0

19.2

31.4

24.4

1.667

23.0

19.1

32.4

24.6 .

FXVII

1.726

1.26

22.3

18.6

31.3

24.1

H XVII

1.730

1.36

23.9

19.8

33.7

25.6

1.728

23.1

19.2

32.5

24-9

F XVIII

1.839

1.32

22.3

18.5

33.2

24.7

H XVIII

1.823

1.29

23.0

19.0

32.4

24.5

1.831

22.7

18.8

32.8

24.6

FXIX

1.924

1.29

22.7

18.2

33.2

24.6

HXIX

—

—

—

—

—

—

1.924

22.7

18.2

33:2

24.6

FXX

2.054

1.23

21 .2

17.1

33.2

24.2

HXX

2.004

1.31

22.0

17.9

33.8

24.9

2.029

21.6

17.5

33.5

24.6

GROWTH OF THE CEREBRAL CORTEX

129

IV. GROWTH IN THE DIAMETERS OF THE CELL BODY AND OF THE

NUCLEUS

Chart 1 shows graphically the data given in table 3. As ordinates the average diameters of the cell body and of the nucleus of the pyramids (lamina pyramidalis) and of the ganglion cells (lamina ganglionaris) are jDlotted on the abscissa for the aveiage brain weights.

D iameter in micra

^^_

,^

.-0 — '^

GC

x^

..—

XX.,

—

— „

_.o—

~"^

/

/

y

.y

r

X

XX

- —

_,

/

/■

/

-„

^.o—

--^

--»-.

^.o

-0

--.

.-,—

-».

y

/<

PC

1

r^

/

/

y

l^

-n

^5""

~^

—

i

1

/

a^

^

Tti

/

/

/

/'

^

/

//

/

/

/

/

/

/

O.i OZ B 03 Q4 Q5 Q6 07

0.9 10 \\ 12 13 14 15 16 17 18 1.9 %()

^s

Chart 1 Showing the corrected average diameters of the cell body and the nucleus of the cortical nerve cells of the albino rat, plotted according to increasing brain weight. Based on the data in table 3. Graph GC, average diameter of the cell body of the ganglion cells in the lamina ganglionaris. Graph GN, average diameter of the nuclei of the ganglion cells in the lamina ganglionaris. Graph PC, average diameter of the cell body of the pyramids in the lamina pyramidalis. Ciraj^h PN, average diameter of the nuclei of the pyramids in the lamina pyramidalis. X, 10 days of age. XX and *, 20 days of age. **, 30 days of age.

130 NAOKI SUGITA

If the length of the average diameters represents relatively the cube root of the volume of the cell body or of the nucleus, the actual volume of them may be comparable among themselves by the cube of the diameters. It is clearly seen from the chart that the pyramids in the lamina pyramidalis of the Albino cortex attain their maximum size in a brain weighing from 1.1 to 1.3 grams or 20 to 30 days in age, the curve showing the maximum size in a brain weighing about 1.25 grams, and after that they diminish slightly but steadily in size as the age (brain weight) advances, while, on the other hand, the ganglion cells in the lamina ganglionaris attain nearly their full size in a brain weighing about 0.95 gram or ten days in age; that is, earlier than the pyramids, and after that slowly but steadily increase their size as the brain weight increases. The nuclei in the pyramids and in the ganglion cells change their sizes in much the same way as the cell bodies to which they belong, the graphs for the cell body and that for the nucleus for each kind of cell running nearly similar courses (chart 1).

As shown in chart 1, the graphs suggest that both kinds of cells increase in size very rapidly during the first ten days after birth, and then the rate diminishes rather abruptly during the following ten days (0.95 to 1.15 grams in brain weight) or more, at the end of which phase the pyramids reach the maximum size, after which they decrease slowly, while the ganglion cells still continue to increase somewhat even after this phase.

On examining all the sections which I made, it was seen that the ground tone of the sections uniformly stained with the carbol-thionine has been gradually changing as the age of the brain, from which the sections were taken, increases. In successfully stained sections — even if stained by decoloration — of brains from birth to those weighing less than 1.0 gram, the ground tone is rather purple or violet, when viewed Avith the naked eye by transmitted light. On the other hand, the sections from brains weighing more than 1.3 grams have a rather distinctly blue tone. The intercellular tissue takes more easily the pale blue color — owing to a less decoloration — in older brains, while in younger brains the intercellular tissue remains

GROWTH OF THE CEREBRAL CORTEX 131

quite unstained. The period during which the brain weiglit increases from 1.1 to 1.3 grams coincides with a transitional phase of the color. I regret that I have not been able to reproduce these distinctions of color for the illustration of this paper.

These changes in color suggest that at the 20 to 30 day phase some chemical changes in the structure of the cell body and the nucleus have been occurring.'- At this phase of growth, the cells having attained nearl}^ the full size, the rate of increase in size abruptly diminishes, suggesting that during this phase important changes have occurred. Myelination is proceeding very activel}^ after the brain has attained the weight of 1.0 gram (Sugita, '17 a), and the fact that the cell bodies and nuclei of the pyramids decrease in size as the brain weight passes 1.3 grams while the growth of the cell body and of the nucleus of the ganglion cells become very slow may have some connection with the myelin formation.

Table 3 enables us to examine the measurements for the frontal and for the horizontal sections separately. Generally speaking, at the locality VII, measured in the frontal section (lines denoted by F in table 3) and at the locality X measured in the horizontal section (see lines denoted by H in table 3), the corrected sizes of the cell body and of the nucleus show some differences in the younger brains, but the sizes may be regarded on the whole as practically the same in these two localities in mature brains. If stated more minutely according to the data presented in table 3, the pyramids and the ganglion cells at locality VII (frontal section) grow in size somewhat more slowly as compared with those at locahty X (horizontal section), so that in Groups IV to X the diameters are all smaller for the frontal section than for the horizontal section, in averaged values (see table 3). But if these slight discrepancies be not

2 As noticed in tables 1 and 2, the size of the ganglion cells directly measured on the slides shows a slight decrease during this phase (1.0 to 1.3 grams in brain weight), while, in corrected measurements given in table 3, there cannot be detected any diminution in cell size during the same phase. This decrease in size of the ganglion cells on the slide may have some connection with the chemical changes occurring in the cytoplasm and karyoplasm, which cause different reactions to the reagents used for fixation.

132

NAOKI SUGITA

taken too seriously, it may be stated that on the average the cell bodies and the nuclei of the pyramids attain their maximum size at about tAventy-five days (brain weight, 1.25 grams) and those of the ganglion cells attain nearly the full size at about ten days of age (brain weight, 0.95 gram).

The largest ganglion cells (lamina ganglionaris) in the cerebral cortex of the adult albino rat brain are found in the middle part of the sagittal section, denoted by locality III (Sugita, '17 a). The size of these largest cells at different ages was not systematically investigated by me, but a careful comparison of them with the ganglion cells at localities VII and X, tabulated in this study, show them to be on the average (in brains weighing more than 1.3 grams) 4 to 7 micra greater in the transverse diameter, 7 to 10 micra greater in the longitudinal diameter of the cell body, and 3 to 5 micra greater in both diameters of the nucleus — all in corrected values — than the corresponding diameters of the ganglion cells in localities VH and X, as shown in the following summary :

Average corrected diameters of the cell body and of the nucleus of the ganglion cells in the lamina ganglionaris {Groups XIII-XX)

Cell body. Nucleus. . .

LOCALITIES VII AND X

28 X 37 M (average 32.4 ju) 24 X 25 ;u (average 24.4 ;u)

LOCALITY III

33 X 46 M (average 39.0 m) 28 X 30 yu (average 29.0 m)

The size of the cell bodies and their nuclei in the other layers of the Albino cortex will be considered in a later chapter in this paper.

Figures 3 and 4 give the typical appearance of the pyramids and the ganglion cells, respectively, for each brain-weight group (with a few omissions), all drawn proportional in size to the uncorrected diameters and magnified about 950 times.

V. MORPHOLOGICAL CHANGES IN THE CORTICAL NERVE CELLS

DURING GROWTH

Figures 3 and 4 illustrate the typical pyramids and the ganglion cells from each brain-weight group, as seen in the sections pre

GROWTH OF THE CEREBRAL CORTEX

133

pared by me, from the material fixed in Bouin's fluid, imbedded in paraffine, stained with the carbol-thionine, and projected and enlarged by a fixed number of diameters. The size of the pictures, therefore, corresponds to the uncorrected measurements given in tables 1 and 2.

Though they are increasing in volume very rapidly after birth, the pyramids in the lamina pyramidalis retain up to a brain weight of 0.6 gram (VI, 6 days in age) the characteristics of the

Fig. 3 Showing somi-diagrammatically the increase in size and the morphological changes, in the typical pyramids in the lamina pyramidalis of the cerebral cortex of the albino rat. The Roman nmnber by each cell figure indicates the brain weight group from which the typical pyramid was selected and the drawing made. All cell figures have been uniformly magnified to 950 diameters, according to the uncorrected measurements.

134

NAOKI SUGITA

Fig. 4 Showing scmi-diagraminatically the increase in size and the morphological changes in the typical ganglion cells in the lamina ganglionaris of the cerebral cortex of the albino rat. The Roman number by each cell figure indicates the brain-weight group from which the typical ganglion cell was selected and the drawing made. All cell figures have been uniformly magnified to 950 diameters, according to the uncorrected measurements.

GROWTH OF THE CEREBRAL CORTEX 135

fetal form of the cells, ^ represented by a relatively large, round nucleus thinly enveloped by a small amount of homogeneous cytoplasm and with processes from both poles. The Nissl bodies begin to appear first in a brain weighing 0.8 gram (VIII), showing first in a part of cytoplasm adjoining the nucleus at the apical pole and forming the so-called 'Kernkappe.' The cytoplasm matures rapidly in structure as the brain weight increases from 0.8 to 1.2 grams. As the measurements show, the nucleus attains nearly the full size when the brain weighs 0.95 gram (10 days), but at that phase the cytoplasm has not yet been fully developed. It is meagre in mass, enveloping the nucleus thinly,

Fig. 5 iShowing the cerebral cortex proper at the locality II (fig. 2, Sugita, '17 a) on a fetal brain of the albino rat. Body weight about 1.0 gram, body length (neck-rump) about 19.5 mm., eighteenth day of gestation. Magnification of about 500 diameters, measured directly on the slide.

the Nissl bodies not being yet fully differentiated, but only suggesting the 'Kernkappe.' The cell continues to grow very slowly up to a brain weight of 1.1 to 1.3 grams or about 20 to 30 days in age. Then, as the age advances, the sizes of both the cell body and of the nucleus slowly diminish, while within the cytoplasm the differentiation of the Nissl bodies progresses. As the differentiation progresses, the general tone of color of the section

^ The form of the fetal nerve cells from the locality II of the cerebral cortex of the albino rat is shown diagrammatically in figure 5, which was taken from an Albino fetus of 1.0 gram in body weight, 19.5 mm. in body length at the eighteenth day of gestation. The cortex proper, not regarding the transitional layer, consists of four or five rows of cells with scanty cytoplasm. The average diameter of the nucleus is about 5 to 7 micra on the slide and the thickness of the cortex at this age is about 0.06 mm. on the slide.

136 NAOKI SUGITA

changes from violet to blue, owing to the deeper staining of the Nissl bodies and of the intercellular tissue with the carbolthionine. The apical dendrite thickens rapidly during the period in which the brain weight increases from 1.0 to 1.3 grams, but the basal dendrites are not clearly stained until the brain attains 1.6 grams in weight. Throughout the later life, the cytoplasm is slowly but continuously decreasing in the absolute mass as the age advances, and the size of the nucleus is also diminishing. The nucleolus in the nucleus attains also its full size (the diameter is somewhat less than 2 micra) at the time when the nucleus has attained the maximum size, but it tends to grow shghtly in late rages, w^hile the nucleus show some decrease in size.

The structure of the nucleus of the pyramids is not clearly demonstrable with this stain. As far as can be judged from the present preparations, the chromatin substance in the nucleus begins to develop notably only after the brain has attained the weight of 1.0 gram, and after the nucleus has passed its phase of rapid enlargement.

From the foregoing it will be seen that up to a brain weight of 0.95 gram, the pyramids may be regarded as in the preparatory stage of structural development, attaining at the end of this period nearly the full size of the cell body and of the nucleus. And after this stage increase and differentiation in the cytoplasm and the nucleus chromatin continue slowly until a brain weight of 1.1 to 1.3 grams. After that time they begin rather to diminish in size, but nevertheless, to advance more and more in differentiation, which latter change probably indicates the maturing of the function of the pyramids. Morphologically, the pyramids first attain their fully mature aspects at a brain weight of about 1.6 grams (about 50 days in age).

In my previous studies on the development of the cortex (Sugita, '17 a, '18 b), I named three phases of cortical growth in the early life of the albino rat; the first phase: from birth to the tenth day; the second phase: from the tenth to the twentieth day, and the third phase: from the twentieth to the ninetieth day. Applying this series of phases to the cytological development of the pyramids, the following appears.

GROWTH OF THE CEREBRAL CORTEX 137

In the first phase occurs the rapid enlargement of the cell body and the nucleus, the cell retaining still the fetal form, and not showing any significant differentiation in the internal structure. The Nissl bodies first appear as the so-called ' Kernkappe' at the end of this phase. The tone of color of the sections stained with the carbol-thionine is rather violet.

In the second phase, the size of the cell body and of the nucleus continues to increase, but very slowly, and both attain their maximum sizes at the end of this phase. The differentiation in cytoplasm goes slowly on and the chromatin in the nucleus begins also to differentiate. The tone of the stain is transitional from violet to blue.

Throughout the third phase and afterwards, the size of the cell body and of the nucleus decreases slowly from the maximum values attached at the end of the second phase. But the differentiations of the cytoplasm and the nucleus chromatin steadily continue as the age advances. The apical dendrites gain in diameter and the basal dendrites begin to take the stain. The nucleus sometimes shows the 'Kernfalte.' The tone of the stain is rather blue and the contour of the pyramids clear cut.

The ganglion cells of the lamina ganglionaris enlarge very rapidly and attain nearly their full size at the age of ten days — somewhat earlier than do the pyramids. But the morphological changes which take place in the ganglion cell body and the nucleus are similar to those just described in the pyramids. In the lamina ganglionaris there can be recognized two distinct kinds of nerve cells, one the smaller-sized pyramids, which seem to be very like the pyramids in the lamina pyramidalis, and the other, the larger-sized neurons, which are usually called ganglion cells or giant cells and which characterize the layer. Some of the cells found in the lamina ganglionaris and which grow to be the ganglion cells are from the first somewhat large-sized. These develop more rapidly than the other small cells in this layer, which are intermingled with them. In earlier stages the ganglion cells manifest no structural difference or characteristics marking them off from the smaller cells, but differ only in the size of the cell body and of the nucleus. They retain their fetal

138 NAOKI SUGITA

appearance, that is, an ovoid form with a relatively large nucleus also ovoid or ellipsoid in form and a small amount of envelop-: ing cytoplasm, which seems almost homogeneous in its staining, together with slender processes, until a brain weight of 0.75 gram. The Nissl bodies begin at first to appear in a brain weighing 0.9 gram, as the 'Kernkappe' covering the apical part of the nucleus. The differentiation of the cytoplasm becomes more and more distinct as the brain weight increases and, in brains weighing more than 1.3 grams, the section as a whole takes a blue tone. This change in color tone is probably due to the development of the Nissl bodies in the cytoplasm and the structural changes in the intercellular tissue. The apical dendrites rapidly thicken in brains weighing 1.1 to 1.3 grams and, in brains weighing more than 1.3 grams, we see distinctly some relatively thick basal dendrites and the axis-cylinder becomes visible. The mass of the cytoplasm and the differentiation of the Nissl bodies proceeds steadily as the age advances. In the fully grown brain we see very often small satellite cells surrounding or indenting the cytoplasm of the ganglion cells, though satellite cells appear in relation to some other types of neurons also. Whatever the significance of these satellite cells, it is to be noted that in younger brains they are very rarely seen. The outline of the ganglion cell body is not necessarily sharp nor is the form regularly pyramidal, being sometimes indeed quite irregular and often appearing ovoid or ellipsoid in shape. Lipochrome or fat pigment, usually seen in the adult human cells of this type, is never seen in those of the adult albino rat, even in old age.

The nucleus of the young ganglion cell seems quite simple in structure and it attains nearly the full size in a brain weighing 0.95 gram. After passing this stage, the chromatin structure of the nucleus begins to appear. The size of the nucleus may be said to remain practically the same after this stage, while the cytoplasmic development continues relatively rapidly. The 'Kernfalte' is sometimes visible in brains weighing more than 1.5 grams. The nucleolus in the nucleus of the ganglion cells attains also nearly the full size (diameter is somewhat less than 4 micra) at the phase when the nucleus has reached nearly

GROWTH OF THE CEREBRAL CORTEX 139

the full size (10 days), but continues to grow steadily, though slightly, throughout later life. The size of the nucleolus in the ganglion cells is relatively much larger than in the pyramids.

As for the developmental phases of the ganglion cells according to age, a statement similar to that made concerning the pyramids of the lamina pyramidalis holds true, though in the ganglion cells the size development seems to be accomphshed in general somewhat earlier. In a brain under 1.2 grams in weight, more mature ganglion cells are seen mixed up with those less mature, indicating that the development of the ganglion cells is not uniform, but that some progress more slowly. In a brain weighing more than 1.3 grams, all the ganglion cells seem to have already passed the first phase of development in size, and all the cells are now of full size and probably fully functional.

One observation which I think it important to notice here is that cells in the same layer but in different parts of the cortex do not always show a like degree of development at a given age. Some cells or some cell groups are more precocious or more retarded than their neighbors. My observations apply only to the size and morphology of the most developed cells found together in a selected locality, regardless of the relative maturity of that locality. So the statement that the ganglion cells attain full size at ten days does not necessarily mean that the lamina ganglionaris is completely mature at that age, but it only applies to the size or morphology of the most advanced cells found in the layer. As a matter of fact, the lamina ganglionaris matures in toto earliest, so that in a brain weighing 1.3 grams all the ganglion cells found in the lamina ganglionaris are apparently completely mature, while at the same age the lamina pyramidalis still contains many immature cells among the mature ones, and the full maturity of the latter layer is attained only in a brain weighing more than 1.6 grams (more than 50 days in age).

In respect of cell size and morphological changes, the lamina ganglionaris and the lamina multiformis are the earliest to mature all the elements in them, while the lamina pramidalis matures more slowly, for example, and in a section from a brain twenty days old, we can still see many immature cells mixed with the mature ones in this latter layer.

140 NAOKI SUGITA

VI. ON THE NERVE CELLS IN OTHER LAYERS OF THE CEREBRAL

CORTEX

Figure 6 shows a diagram of cell-lamination of the adult albino rat brain, taken from locality II of the sagittal section (fig. 2, Sugita, '17 a). In comparison with the data on the pyramids in the lamina pyramidalis (III) and the ganglion cells in the lamina ganglionaris (V), the measurements of the cells found in the lamina granulans interna (IV) and the lamina multiformis (VI) show nothing peculiar. Generally speaking, the cell body and the nucleus of the granules do not take the stain as well as in the case of the pyramids and remain rather pale in color. The cells of the lamina multiformis, on the other hand, generally stain deeply. Especially the cytoplasm of the cells forming the inner (ental) sublayer of the lamina multiformis tints very well, so that this sublayer is easily distinguished even at a low magnification by the deep staining of the elements.

The granules in the lamina granulans interna (IV) are smaller in size and lie more crowded than do the pyramids. This layer is not clearly differentiated in brains weighing less than 0.6 gram or less than six days of age, at which stage the immature cells of fetal form prevail in both the lamina pyramidalis and the lamina granularis interna and no characteristic granules are shown. On the sections from a brain weighing 0.5 to 0.6 gram, which had been fixed in formaldehyde and imbedded in paraffine, I could see distinctly a dark band due to the deep staining of the ground substance and characteristic for the adult lamina granularis interna (cf. Sugita, '17 a, p. 526), though the contained cells do not show any of the characteristics of the granules. This is probably the first step in the differentiation of the granular layer. Later we see that the cells lying near the lamina ganglionaris become more and more crowded and somewhat small in size compared with the cells lying in the lamina pyramidalis. In an adult brain weighing more than 1.3 grams, a distinct band of smallersized cells (the lamina granularis interna) appears above the lamina ganglionaris.

GEOWTH OF THE CEREBRAL CORTEX

141

Fig. 6 Diagram of cell-lamination of the frontal cerebral cortex (locality II, fig. 2, Sugita, '17 a) of the adult albino rat brain weighing 1.8 grams, schematically enlarged 66 diameters. I = lamina zonalis, III = lamina pyramidalis, IV = lamina granularis interna, V = lamina ganglionaris, VI = lamina multiformis, which is divided into two sublayers at * by a.band poor in cells.

|ll#'?-'

Mm

J'o V *

■A . f

o»^

Mil

>VI

SaJt- fc'^Jc ^ VT^ ' C jag

THE JOTIRNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 2

142

NAOKI SUGITA

TABLE 4 Giving both corrected and the uncorrected values for the two diameters of the cell body and the nucleus respectively, of the granule cells in the lamina granularis interna {IV, fig. 6) for several brain weight groups

BRAIN WEIGHT GROUP

Group II (birth)

Group III

Group V

Groups VI-VIII

Groups X-XIII

Groups XIII-XV

Groups XVI and above

CELL BODY

Corrected

M

12x15 14x16 15x18 16x20 19x21 16x20 15x20

On the slide

M (10 X 12) (11 X 13) (12 X 14) (13 X 16) (15 X 17) (13 X 16) (12 X 16)

Corrected

11 xl2 12x14 14x15 15x16 16x19 15x16 14x16

On the slide

M

(9 X 10)

(10 X 11)

(11 X 12) (12 X 13) (13 X 15) (12 X 13) (11 X 13)

The average size of the granules measured on the sections here used is given in table 4. In brain-weight Groups II-V, at which stages the layer is not yet clearly differentiated, the measurements were made on the small cells which lie nearest to the lamina ganglionaris and the cells were assumed to be the future granules.

So, in brains weighing more than 1.6 grams (Group XVI), the size of the granules diminishes shghtly as the age advances. Most of the nuclei of the granules are more or less elongated or elliptical in shape and the cytoplasm is very scanty, so that sometimes there can be seen only a thin envelope of the cytoplasm around the nucleus.

In short, the granules at the earlier age are ahnost equal to the growing pyramids in size, but they increase in size somewhat less rapidly as compared with the pyramids, among which they are interspersed at first. They reach their maximum size in a grain weighing between 1.2 and 1.4 grams, and after that period the size decreases as the age advances, showing ^ somewhat compact nucleus.

As already indicated in a former paper (Sugita, '17 a), the lamina multiformis is divided by a pale band (fig. 6,*), poor in cells, into two sublayers. The polymorphous cells in the ectal sublayer have the shapes indicated by their name, but in general they are pyramidal in form, the apex directed ectally, being somewhat flattened and rich in cytoplasm, as compared with the

GROWTH OF THE CEREBRAL CORTEX 143

pyramids. The density of the polymorphous cells in this sublayer is greatest at the earlier ages. During the early ages the most densely crowded pyramids are in the lamina pyramidalis, while by contrast the lamina multiformis seems rather poor in cells. But in adults the cell population of the ectal sublayer of the lamina multiformis appears to be only slightly less than that of the lamina pyramidalis and the size of the polymorphous cells appears nearly equal to that of the pyramids, though, by an exact measurement, they prove to be slightly larger (fig. 6). The shape of polymorphous cells is not uniform and they show many dendritic processes, irregularly arranged. Some, though pyramidal, lie obliquely or transversely, while some hold a reversed position, with the apical dendrite directed entally (Martinotti's cells).

The cells of the ental sublayer of the lamina multiformis are quite different in their appearance. They are polygonal or spindle-shaped and generally lie with their long axis in the plane of the lamina. The cytoplasm of the cells is massive and takes the stain well. The Nissl bodies, however, are not well differentiated. Though not always pyramidal in shape, the assumed apex of the cells appears to be directed towards the occipital pole in the sagittal and the horizontal sections or towards the ventral surface in the frontal section, thus indicating the direction of the migration of the nerve cells from the matrix to the cortex proper. As already stated by me (Sugita, '17a), this sublayer probably serves as a secondary station for cells migrating from the matrix at the ventricular wall to their final destination in the cortex and the number of cells in this sublayer diminishes as the age of the brain advances. So one has some reason to think that a fraction of the cells found in this sublayer are still in transit, at least during the early ages. It should be noted at least that the cells of this sublayer have a morphology in respect of the mass and the staining reaction of their cytoplasm which indicates the stage of migration.

The neuroglia nuclei are abundantly scattered in the ental cortical layers (that is, in the lamina multiformis and the lamina ganglionaris) as compared with the ectal layers (that is, in the

144

NAOKI SUGITA

TABLE 5

Giving the cubes of the average diameters of the cell bodies and of the nuclei of both the pyramids {lamina pyramidalis) and the ganglion cells (lamina ganglionaris) at birth, 10 days, 20 days and 90 days, the ages indicating respectively the beginning of each developmental phase. The values given represent merely the relative volumes of the cell bodies and of the nuclei. Ratios based on the initial value taken as unity are given for each column. The data, on the basis of which the calculations were made, were taken from table 3

BRAIN WEIGHT GROUP

PYRAMIDS IN THE LAMINA PYRAMIDALIS

GANGLION CELLS I.N THE L.tMINA GANGLIONARIS

THE BEGINNING OF EACH

Cell

body

Nucleus

Cell body

Nucleus

DEVELOPMENTAL STAGE

S5 >

la

> o

M

o

> <o

Pi >

_0

^ 3 Ph >

.2

1

Birth

II

IX

XI

XVIII

m3

215 1185 1315 1170

1.00 5.51 6.12 5.44

m3

119

775 790 665

1.00 6.50 6.63

5.58

m3

675 2925 3070 3530

1.00 4.33 4.55 5.23

m3

330 1440 1415 1490

1.00

10 days

4.36

20 days

4.29

90 days

4.52

lamina granulans interna and the lamina pyramidalis) (see fig. 6). At earlier ages, neuroglia nuclei are comparatively scarce in the lamina pyramidalis, but at maturity they are well distributed in this layer, though in the lamina multiformis they are found always abundantly. With the method of . staining here used, we can distinguish two kinds of the neuroglia nuclei, one staining a relatively deep blue, which is the smaller in size (2 to 5 micra in diameter on the slide) , with crowded granules in the chromatin sometimes arranged radially ('Radkern'), and surrounded by evident cytoplasm, and the other staining rather paler and with a violet tone, vesicular ('blasig') in appearance, somewhat larger in size (3 to 6 micra in diameter on the slide) , with scanty chromatin and enveloped by a small amount of cytoplasm. This metachromatism in the staining of the two kinds is very remarkable. Both kinds are found intermingled. In the white matter glia cells are distributed in rough chains, while in the cortex they are, under normal conditions, less well distnbuted than in the white matter. Sometimes, especially in old age, the glia cells are found gathered around the ganghon cells or the pyramids or near the blood-vessels. The satelhte cells which are attached to or

GEOWTH OF THE CEREBRAL CORTEX 145

even invade the cytoplasm of the nerve cells, are usually regarded as neuroglia cells.

vThe method here used, of staining with the carbol-thionine the material fixed in Bouin's fluid and imbedded in paraffine, reveals clearly only the size and shape of the nerve cells in the cerebral cortex. The more detailed structure of the cytoplasm and of the nucleus or the structure of the axis-cylinder and dendrites is not brought out by this method, and for the investigation of these characters other methods are required.

VII. DISCUSSION

According to the foregoing observation, the full size of the largest pyramids in the lamina pyramidalis (about 25 daj^s in age)^ is about 21 x 27 /x for the cell body and 19 x 21 n for the nucleus, and the measurement of those largest atbirth^ is 11 x 15 /x for the cell body and 10 x 11 m for the nucleus, in the fresh condition of the material. The full size of the largest ganglion cells in the lamina ganglionaris (at localities VII and X, about 25 days, for example)"* is 27 x 37 /j. for the cell body and 24 x 25 fx for the nucleus, and the measurement of the largest ganglion cells at birth^ is 17x21 /x for the cell body and 14x16 /x for the nucleus, all in the fresh condition of the brain.

If the volume of the cell bodies or of the nuclei be comparable among themselves according to the cubes of their average diameters, the figures given in table 5 "vvhich presents the cubes of the average diameters of the cell bodies and of the nuclei of the nerve cells at different ages, and which were calculated from the data in table 3, may be used as the basis of discussions on the volume development of the cells. It will be seen from table 5, by a

■* To obtain the values here given, the uncorrected diameters of the cell body and the nucleus in Groups XI-XIII in the frontal and the horizontal sections (tables 1 and 2) were respectively averaged and the results were corrected b^ multiplying by the mean correction-coefficient of Groups XI-XIII for the frontal and the horizontal sections (see table 3).

To obtain the values here given, the uncorrected diameters of the cell body and the nucleus in Group II in the frontal and the horizontal sections (tables 1 and 2) were respectively averaged and the results were corrected by multiplying by the mean correction-coefficient of Group II for the frontal and the horizontal sections (see table 3).

146 NAOKI SUGITA

simple calculation, that at birth the largest ganglion cells are almost 3.1 times as voluminous, at 20 days about 2.3 times, and at 90 days 3.0 times, as the pyramids of the same stage, and the nuclei of the ganglion cells are at birth 2.8 times as voluminous, at 20 days 1.8 times, and at 90 days, 2.2 times as the nuclei of the pyramids of the same stage, if both kinds of cells are assumed to have the similar forms throughout their enlargement.^ It is also seen that, using the same method, the cell body of the pyramids has increased from birth 6.1 times in volume at 20 days and 5.4 times at 90 days, and the nuclei 6.6 times at 20 days and 5.6 times at 90 days, while the cell body of the ganglion cells has increased only 4.6 times at 20 days, 5.2 times at 90 days and the nuclei of the ganglion cells 4.3 times at 20 days and 4.5 times at 90 days, as compared with their initial volumes at birth.

It may therefore be concluded that, throughout the developmental stage of the nerve cells after birth, the rate of enlargement is almost similar in the nuclei and in the cell bodies of both kinds of cells, though the rate is slightly higher in the pyramids than in the ganglion cells in both the cell body and the nucleus during the first twenty days after birth, because the initial volume of the pyramids is small at birth.

As the shape of the cell body is different from that of the nucleus, it is not proper' to compare directly their respective volumes as determined by the foregoing use of their diameters, but they must be first reduced to forms which are comparable as

• Here the nucleus was considered as an ellipsoid, the volume of which is to be calculated by the formula ^ira'^b, when b is the long radius and a is the short radius of the body. As the transverse diameter (n.i) of the nucleus is equal to 2a and the longitudinal diameter (n^) is equal to 26 the volumes of the nuclei may be compared among themselves simply by the factor a-b or ni^nj.

On the other hand, if the volume of the cell body was considered as a circular cone, in which the diameter of the basic circle is equal to the transverse diameter (ci) of the cell body and the height of the cone is equal to the longitudinal diameter (C2) of the cell body, then the volume of the cell body will be

Jtt ( ^ yc2, and the values for the relative volumes of the cell bodies may be compared on the basis of the factor Ci-Cj.

As the average diameters given in table 3 are respectively the square roots of the products nin-i and CiCo, the cubes of the average diameters will be approximately proportional to the values nihi2 and ci^c-2, respectively.

GROWTH OF THE CEREBRAL CORTEX 147

explained in the accompanying note and then table 5 may be consulted again. ^ It is seen from table 5 that at birth the entire cell has almost double the volume of the nucleus, so that the cytoplasm and the nucleus have nearly the same volume. The nucleus-plasm relation changes according to the brain weight. In the pyramids, the total cell body comes to 1.7 times at 20 days and to 1.8 times at 90 days, compared with the volume of the nucleus at the same age. This is owing to the relatively rapid growth of the nucleus. In the ganglion cells, on the other hand, the total cell body is 2.2 times at 20 days and 2.4 times at 90 days, compared with the volume of the nucleus at the same stage. As the pyramids decreases in size after 30 days, the cell size of the pyramids in old age (brain weight more than 2.0 grams) becomes almost equal to that at 8 days of age, but the nucleus-plasm relation is quite different at the two stages. At 8 days the nucleus is relatively large (total cell body is 1.7 or less times the nuclear volume), but in old age the volume of cytoplasm has increased somewhat in relation to the nuclear volume (total cell body is nearly 2.0 times the nuclear volume). These values for comparison were taken from the data here used alone, but, as already noted, sections which were taken from material fixed in 95 per cent alcohol or in Bouin's fluid and imbedded in celloidin show a nucleus which is relatively smaller. In series of sections which have been prepared by methods other than that used by me, the volume relations between the cell body and the nucleus (nucleus-plasm relation) would probably be different from those which I have reported here, but I think it will be fair to assume that the growth changes in the cell body on

^ If the cell body were considered as having an ellipsoidal form with diameters equal to Ci and c^ which denote respectively the transverse longitudinal diameters measured on the cell body the volume, would be \t^( ^ )'{ ^ ) ^'^ ^t^Cx^CiAnd if, on the other hand, the same cell body were considered as a circular cone, the volume may be calculated by 57r( -^ \ ^co, or ^-kc-cCi. As the difference between

these two formulas is not higher than ^ of crC2, I have here compared the

volumes of the cell body and of the nucleus under the assumption that both have the ellipsoidal form, employing once more the figures given in table 5 as the basis of comparison.

148 NAOKI SUGITA

one hand and in the nucleus on the other would probably be similar by the use of any uniform method, even if the absolute values differed for the different methods, and none of them gave exactly the fresh values.

It is remarkable that both the cell body and the nucleus of the cortical cells attain nearly their full size at an early stage of development (at about ten days of age) and then continue to undergo cytomorphic development, without much change in cell size (chart 1). As already pointed out in former papers (Sugita, '17 a, '18 b), the elementary completeness of the cerebral cortex of the albino rat is attained at the age of twenty days, the final thickness of the cortex and the total number of the cortical nerve cells being apparently reached at this age. .\fter this age, the volume of the cortex increases as the age ad\'ances nearly in proportion to, or at a slightly slower rate than, the total volume of the cerebrum. As noted, the size of the pyramidal cells in the lamina pyramidalis attains the maximum size in brains weighing 1.1 to 1.3 grams and the volume of the cell body and the nucleus becomes slightly less during later phases, while the size of the ganglion cells in the lamina ganglionaris increases slightly as the age advances, even after the above-named stage. It must be concluded, therefore, that the subsequent increase in cortical volume is effected by changes in structures other than the cell bodies themselves. And, as a consequence, in mature brains, the cell density in the cortex diminishes more and more, as has been already pointed out in a previous paper (table 3, Sugita, '18 b).

It is very interesting to find that the thickness of the cortex, the total number of the cortical nerve cells, and the size of the cortical cells all have reached nearly their maximum at the same age of twenty days, which is the weaning time of the rat. These relations appear also in the mouse. According to the results obtained by Isenschmid ('11), the thickness of the cerebral cortex of the mouse, measured at a fixed locality — corresponding to locality VII in my sections — attains nearly its full value something before seventeen days in age. And according to the systematic work of Stefanowska ('98), who has studied the devel

GROWTH OF THE CEREBRAL CORTEX 149

opment of the cortical nerve cells by the method of silver impregnation of Golgi, the cortical nerve cells of the mouse have completed their development in respect of their attachments at the age of fifteen days, and the age of fifteen days is the weaning time of the mouse. It appears, therefore, that the completion of certain features of cortical development in relation to the weaning time, the time when the j^oung become independent of the mother, is similar in both the albino rat and the mouse.

VIII. SUMMARY

1. The size of the nerve cells most advanced in development from a fixed locality of the cerebral cortex was systematically^ measured and the developmental changes during postnatal growth studied on the material represented by the grains of 128 albino rats of different ages. The data have been averaged for each brain-weight group and then corrected for the fresh condition of the material, using the correction-coefficients devised for this purpose. The results are given in tables and charts.

2. The full size of the pyramids in the lamina pyramidalis (about twenty-five days in age, average of Groups XI-XIII) is cell body 21 x 27 /j. and nucleus 19 x 21 n and the largest size at birth is cell body 11 x 15 m and nucleus 10 x 11 /x. The size of the ganglion cells in the lamina ganglionaris at the same stage (about twenty-five days in age, average of Groups XI-XIII) is cell body 27 x 37^ and nucleus 24 x 25 fx, while the largest size at birth is cell body 17 x 21 ix and nucleus 14 x 16 n.

In the full-grown albino rat (Groups XVI-XX), the average size of the pyramids is cell body 20 x 26 fj., nucleus 18x19 m and the average size of the ganglion cells is cell body 28 x 38 /jl, nucleus 24 x 25 //.

3. The cell body and the nucleus of the pyramids attain their maximum size at twenty to thirty days in age (1.1 to 1.3 grams in brain weight) . Up to the tenth day of age they retain their fetal morphology. After having passed the maximum at twenty to thirty days, they diminish in size, but the internal structure matures more and more as the age advances.

150 NAOKI SUGITA

4. The cell body and the nucleus of the ganglion cells attain nearly their full size at ten days (0.95 gram in brain weight), when they still show the fetal appearance. After this stage, the size of the cell body increases slowly but steadily as the age advances, while the nucleus remains nearly unchanged in size throughout life.

5. Both the pyramids and the ganglion cells retain clearly the fetal character of form until the brain weighs 0.6 gram or more. The differentiation of the cytoplasm and the Nissl bodies begins to appear in my preparations first in a brain weighing something more than 0.9 gram, the latter showing first as the 'Kernkappe' at the apex of the nucleus. The cells exhibit the mature appearance in a brain weighing more than 1 .4 grams.

6. As for the maturation of the several layers, in general, disregarding the maturation of the individual cells in them, the lamina ganglionaris is completed earliest, so that in a brain weighing 1.3 grams (thirty days in age) all the ganglion cells in this layer are apparently mature, while at the same age the lamina pyramidalis is less mature as it contains relatively many immature cells mingled with the others. The full maturity of the lamina pyramidalis is attained, probably, in a brain weighing 1.6 grams (more than fifty days in age).

7. Throughout the developmental stage of the nerve cells, the rate of enlargement is almost similar in the nucleus and in the cell body in both the pyramids and the ganglion cells ; but when the pyramids are compared with the ganglion cells it appears that' the rate is more rapid in the pyramids than in the ganglion cells in both the cell body and the nucleus during the first ten days after birth.

8. The lamina granulans interna is first differentiated in brains weighing more than 0.6 gram. In younger brains it is confused with the pyramidal layer and cannot be clearly discriminated. The granules attain their maximum size in brains weighing 1.0 to 1.3 grams and then diminish slightly. The final size ( orrected) of the granules in Groups XVI and above, is cell body 15 X 20 // and nucleus 14 x 16 ix.

GROWTH OF THE CEREBRAL CORTEX 151

9. The polymorphous cells in the ectal sublayer of the lamina multiformis are slightly larger than the pyamids of the same age. The polymorphous cells in the ental sublayer of the lamina multiformis are somewhat larger than those of the ectal sublayer, but are irregular in shape and rich in cytoplasm.

10. Two kinds of the neuroglia nuclei are found in the cortex. One staining deep blue with the carbol-thionine, smaller in size (2 to 5 micra in diameter on the slide) and having a radiating structure of the chromatin, and the other staining paler, swollen ('blasig') and somewhat larger in size (3 to 6 micra in diameter on thp slide).

11. Taking a general view of the d^ta already presented in this series of studies, it is very interesting to note that the thickness of the cortex, the total number of the cortical nerve cells, and the size of the cortical cells all attain nearly their full values at the same age of twenty days (1.15 grams in brain weight) ; that is, at the weaning time of the albino rat.

PART II

ON THE INCREASE IN SIZE OF SOME NERVE CELLS IN THE CEREBRAL CORTEX OF THE NORWAY RAT (mUS NORVEGICUS) COMPARED WITH THE CORRESPONDING CHANGES IN THE ALBINO RAT

To compare with the results of the preceding study on the growth in size of the cortical nerve cells in the albino rat brain, data were gathered for the cortical cells of the Norway rat also. According to my previous studies (Sugita, '17 a, '18 a, '18 b), the measurements of the cerebral cortex in the Norway rat in thickness, in total number of cells, etc., have shown some interesting relations to the corresponding measurenients for the Albino. Donaldson and Hatai ('11) made a comparison of these two animals in respect of their body measurements and the size of the central nervous system, and concluded that the greater weight of the brain in the Norway rat is probably due to an enlargement of the constituent neurons rather than to an increase in their number. As my former study (Sugita, '18 b) has de

152

NAOKI SUGITA

TABLE 6

Giving the average uncorrected diameters of the nerve cells and their nuclei in the lamina pyramidalis and the lamina gangi.ionaris measured at the fixed, locality {locality VII) on the frontal sections of the Norway rat brain. The data are given for each brain iveight group only. This table is comparable with table 1

XO. OF

BRAIN

BRAIN- WEIGHT

GROUP

CASES

WEIGHT

grams

NXI

3

1.164

NXIII

1

1.369

NXIV

6

1.430

NXV

3

1.546

NXVI

3

1.629

N XVII

4

1.739

N XVIII

2

1.829

NXIX

2

1,972

NXX

2

2.052

NXXI

2

2.172

N XXIII

1

2.345

LAMIN'.^ PYR.AMIDALIS

Cell body diameter

Transv. Longit

15.2 15.5 15.4 14.8 14.6 14.9 15.0 14.8 14.5 14.3 14.6

20.8 20.9 20.6 19.8 19.8 20.4 20.7 19.4 19.8 20.0 21.0

Nucleus diameter

Transv. Longit

14.5 14.4 14.2 13.8 13.4 13.8 14.1 13.9 13.6 13.3 13.3

15.5 15.5 15.1 15.1 14.1 14.7 14.8 14.3 14.3 14.2 13.9

LAMIXA GANGLIONARIS

Cell body diameter

Transv. Longit

20.5 20.6

21.6 20.5 21.2 21.9 23.5 24.3 23.9 23.9 25.0

29.0 29.9 29.6 28.9 29.0 29.8 32.8 33.7 33.2 34.0 36.0

Nucleus diameter

Transv. Longit

18.1 18.3 18.4 17.8 17.8 18.9 20.7 20.3 20.3 19.4 18.51

19.3 20.2 19.4 19.6 19.2 20.2 21.5 21.6 21.6 21.0 20.51

1 In this group the size of the nucleus of the ganglion cells has fallen down remarkably (see also chart 2), which fact was not seen in the Albino (Group XX). Whether this is due to an actual change in old age or due to incidental variation cannot be definitely affirmed here.

termined that in both fornivS the total number of the nerve cells in the cerebral cortex is practically the same, it becomes desirable to compare the size of the nerve cells in the two animals in order to test the assumption of the above authors.

The material used in. this study comprised 54 Norway rats, sexes combined, the data for which are given in tables 1 and 2 in a former paper (Sugita, '18 a) and which are the same material that was formerly employed for the other measurements on the cortex. It seems unnecessary to repeat these tables here. »

In the selection of the localities in which the largest cells in the lamina pyramidalis and the lamina ganglionaris were measured and in making the measurements, the same procedure was followed as has been described minutely for the albino rat in part I of this paper.

GROWTH OF THE CEREBRAL CORTEX

153

TABLE 7

Giving the average uncorrected diameters of the nerve cells and their nuclei in the lamina pyramidalis and the lamina ganglionaris measured at the fixed locality {locality X) on the horizontal sections of the Norway rat brain. The data are given for each brain weight group only. This table is comparable with table 2

BRAIN WEIGHT GROUP

NXI

NXIII

NXIV

NXV

NXVI

NXVII

X XVIII

NXIX

NXX

NXXI

X XXIII

NO. OF

BRAIN

CASES

WEIGHT

grams

3

1.164

1

1.343

5

1.447

2

1.520

4

1.663

4

1.747

2

1.843

1

1.953

2

2.018

2

2.156

1

2.345

LAMIN.l. PYRAMIDALIS

Cell body diameter

Transv. Longit.

15.4 15.2 15.4 14.8 14.9 14.8 14.5 15.1 15.5 14.7 15.0

20.3 19.9 20.6 20.2 20.0 20.0 20.2 20.8 21.1 20.9 20.8

Nucleus diameter

Transv. Longit

14.1 14.1

14.4 13.9 13.8 13.7 13.8 14.5 14.2 13.8 13.4

15.4 15.1 15.3 15.1 14.9 15.0 14.7 15.3 14.7 14.4 14.0

LAMINA GANGLIONARIS

Cell body diameter

Transv. Longit

20.6 20.4 20.8 20.5 21.0 20.9 20.2 23.5 23.5 23.0 25.8

29.3 28.2 29.0 28.8 29.8 29.5 29.4 30.5 31.0 29.4 32.0

Nucleus diameter

Transv. Longit

18.0 17.8 18.4 18.2 18.3 18.5 18.0 19.5 18.8 18.8 18.41

19.2 19.0 19.7 19.0 19.3 19.5 19.5 20.3 19.0 20.0 19.21

1 See note on table 6.

The results of the measurements aire presented in tables 6 and 7 arranged in the same way as in the corresponding tables 1 and 2 for the Albino. Chart 2 shows graphically the data presented in table 8 which gives the average diameters of the cell bodies and the nuclei for each brain-weight group, corrected for the fresh condition of the material, by multiplying by the correctioncoefficient for the group, which is cited from my previous paper (Sugita, '18 a) and explicitly given in table 8 also. Charts 3 and 4 show some comparisons in cell sizes in the two forms. Chart 3 was plotted according to the actual brain weights of the two forms, and chart 4 was plotted, using the same data for the Norway, but entering these according to the brain weights reduced by 18 per cent, which presumably correspond to the brain weights of the Albino at the same age (see Sugita, '18 a), while the data of the Albino were plotted according to the actual brain weight.

154

NAOKI SUGITA

TABLE 8

Giving the corrected final average diameters of the nerve cells and their nuclei in the lamina pyramidalis and the laynina ganglionaris measured on the frontal and the horizontal sections of the Norway rat brain. The average values of the two for each brain weight group are also given. The correction-coefficient for each brain weight group ^ was taken from previous papers (Sugita, '18 a, '18 b). F = frontal section. H — horizontal section.

LAMINA PYRAMIDALIS

LAMINA GANGLIONARIS

BRAIN WEIGHT

BRAIN WEIGHT

CORRECTIONCOEFFICIENT

GROUP

Cell body diameter

Nucleus diameter

Cell body diameter

Nucleus diameter

grams

M

M

M

M

FN XI

1.164

1.34

23.8

20.1

32.7

25.0

HNXI

1.164

1.30

23.0

19.1

31.8

24.2

1.164

23.4

19.6

32.3

24.6

F N XIII

1.369

1.33

23.9

19.8

33.0

25.5

H N XIII

1.343

1.39

24.2

20.3

33.4

25.6

1.356

24-1

20.1

33.2

25.6

FN XIV

1.430

1.35

24.0

19.7

34.2

25.5

HNXIV

1.447

1.36

24.2

20.3

33.5

25.9

H39

24-1

20.0

33.9

25.7

FN XV

1.546

1.40

23.9

20.2

34.2

26.2

HNXV

1.520

1.42

24.5

20.5

34.5

26.4

1.533

24-2

20.4

34.4

26.3

F N XVI

1.629

1.40

23.8

19.3

34.7

25.9

HNXVI

1.663

1.34

23.2

19.2

33.5

25.2

1.646

23.5

19.3

34.1

25.6

F N XVII

1.739

1.37

23.8

19.5

35.1

26.7

H N XVII

1.747

1.35

23.4

19.3

33.5

25.7

1.743

23.6

19.4

34.3

26.2

F N XVIII

1.829

1.32

23.2

19.0

36.7

27.8

H N XVIII

1.843

1.39

23.8

19.7

34.0

26.0

1.836

23.5

19.4

35.4

26.9

FN XIX

1.972

1.33

22.5

18.8

38.0

27.9

HNXIX

1.953

1.34

23.6

19.8

35.7

26.5

1.963

23.1

19.3

36.8

27.2

FN XX

2.052

1.36

23.1

18.9

38.3

28.5

HNXX

2.018

1.32

23.9

19.0

35.6

25.0

2.035

23.5

19.0

37.0

26.8

GROWTH OF THE CEREBRAL CORTEX

155

TABLE 8— Continued

L.\MINA PYRAMIDALIS

LAMINA GANGLIONARI8

BRAIN WEIGHT

BRAIN WEIGHT

CORRECTIONCOEFFICIENT

GROUP

Cell body diameter

Nucleus diameter

Cell body diameter

Nucleus diameter

grams

M

M

M

M

FN XXI

2.172

1.39

23.5

19.2

39.6

28.1

HNXXI

2.156

1.34

23-. 5

18.9

34.8

26.0

2.164

23.5

19.1

37.2

27.1

F N XXIII

2.345

1.26

22.0

17.2

37.8

24.6

H N XXIII

2.345

1.28

22.6

17.4

36.8

24.1

2.345

22.3

17.3

37.3

244'

^See note on table 6.

Chart 2 shows for the Norway also that the gangHon cells are enlarging slowly but steadily throughout life, while the pyramids rather decrease in size slightly in later life, after having attained the maximum size in brains weighing 1.3 to 1.5 grams. So, in the Norway as in the case of the Albino, the pyramidal cells in the lamina pyramidalis undergo some diminution in the adult brain.

Chart 3 gives a comparison of the cell sizes in brains of like weight in the two forms. In Group N XI, the sizes of the cell body and the nucleus of the pyramids are slightly smaller in the Norway than in the Albino. This is probably explicable by the fact that the Norway brain at this stage is still immature and younger than the Albino brain of like weight. Such a relation has been revealed in other measurements also; for example, in the cortical thickness, the cortical area, etc. (Sugita, '17 a, '18 b). The ganglion cells in the Norway are larger than in the Albino and the difference in the size of the ganglion cells in the two forms increases somewhat as the brain weight advances.

In Groups above N XIII, the ceU size (pyramidal and ganglion cells) in the Norway proved to be generally larger than that in the Albino of the same brain weight.

The summary in table 9 gives the average diameters for the adult Albino (Groups XIII to XX) and the adult Norway (Groups N XIII to N XX).

156

NAOKl SUGITA

TABLE 9

Comparison of diameters of cortical cells in the Norway and the albino rats. The data used here are the averages in Groups XIII to XX and in Groups N XIII to N XX, taken from tables 3 and 8. Differences in diameter and in volume are calcxilated here, the data of the Albino being taken as the standard of comparison

AVERAGE BRAIN WEIGHT

PYR.\MIDS

GANGLION CELLS

Cell body

Nucleus

Cell body

Nucleus

Albino

Norway

grams

1.691 1.694

22.9 23.7

18.8

19.6

32.4 34.9

24.9 26.3

Difference in diameter

Difference in volume

3.5% 10.9%

4.2% 13.1%

7.7% 24.9%

5.6% 17.8%

This summary shows that in mature brains of like weight, the pyramids (cell body and nucleus) in the Norway exceed those in the Albino in average diameters by about 4 per cent and in volume by about 12 per cent, and the ganglion cells (cell body and nucleus) in the Norway exceed those in the Albino in average diameters by about 7 per cent and in volume by about 20 per cent, if the Albino be taken as the standard of comparison. It may be said, therefore, that in the Norway the ganglion cells in the lamina ganglionaris exceed much in size those in the Albino, while the pyramids in the Norway are only somewhat greater than those in the Albino.

In chart 4, which gives a comparison of the nerve-cell sizes between brains of presumably the same age in the two forms, it is shown clearly that the changes in sizes of cell body and the nucleus according to age are quite similar in both forms. The pyramids attain the maximum size at about twenty to thirty days (in the Albino in brains weighing 1.1 to 1.3 grams, in the Norway in brains weighing 1.3 to 1.5 grams, which both come to the same relative position in the curves), and after that they decrease slowly. The ganglion cells in the Norway grow more rapidly than those in the Albino, even in later life. In the latter the ganglion cells remain almost unchanged in size in brains weighing 1.0 to 1.6 grams, while those in the Norway increase in size rather steadily as the age advances.

GROWTH OF THE CEREBRAL CORTEX

157

I

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I

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i i 6 !

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10 11 12 1.3 14 15 16 17 18 19 2.0 21 2.2 23 24 yns.

Chart 2 Showing the corrected average diameters of the cell body and the nucleus of the cortical nerve cells of the Norway rat, plotted according to increasing brain weight. Based on the data in table 7. Graph GC, average diameter of the cell body of the ganglion cells in the lamina ganglionaris. Graph GN ', average diameter of the nucleus of the ganglion cells in the lamina ganglionaris. Graph PC', average diameter of the cell body of the pyramids in the lamina pyramidalis. Graph PN', average diameter of the nucleus of the pyramids in the lamina pyramidalis.

THE JOURNAL OF COMPAE.^^TIVE NEUROLOGY, VOL. 29, NO. 2

158

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Chart 3 Showing a comparison of sizes of the cell bodies and of the nuclei of the ganglion cells in the lamina ganglionaris and of the pyramids in the lamina pyramidalis in brains of the Norway and the Albino, according to the actual brain weights. The data are taken from tables 3 and 7. The chart has been divided and the values 22-26 on the ordinate repeated to prevent confusion among graphs for the cell bodies of the pyramids, PC and PC, and the graphs for the nuclei of the ganglion cells, GN and GN'. In the upper chart: Graph GC, cell body of the ganglion cells in the Norway. Graph GC, cell body of the ganglion cells in the Albino. Graph GN', nucleus of the ganglion cells in the Norway. Graph GN, nucleus of the ganglion cells in the Albino. In the lower chart: Graph PC, cell body of the pyramids in the Norway. Graph PC, cell body of the pyramids in the Albino. Graph PN', nucleus of the pyramids in the Norway. Graph PN, nucleus of the pyramids in the Albino.

GROWTH OF THE CEEEBRAL CORTEX

159

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Chart 4 J Showing a comparison of sizes of the cell bodies and of the nuclei of the ganglion cells in the lamina ganglionaris and of the pyramids in the lamina pyramidalis in brains of the Norway and the Albino, according to age. The Norway brain weight was reduced by 18 per cent and entered at the corresponding brain weight of the Albino. The data were taken from tables 3 and 7. The chart has been divided and the values 22-26 on the ordinate repeated to prevent confusion among the graphs for the cell bodies of the pyramids, PC and PC, and the graphs for the nuclei of the ganglion cells, GN and ON'. In the upper chart: Graph GC, cell body of the ganglion cells in the Norway. Graph GC, cell body of the ganglion cells in the Albino. Graph GN ', nucleus of the ganglion cells in the Norway. Graph GN, nucleus of the ganglion cells in the Albino. In'the lower chart : Graph PC ', cell body of the pyramids in the Norway. Graph PC, cell body of the pyramids in the Albino. Graph PN', nucleus of the pyramids in the Norway. Graph PN, nucleus of the pyramids in the Albino.

160 NAOKI SUGITA

My study of the Norway cortex did not extend to the early life of the animal, but, from the courses of the curves shown in chart 4, it seems probable that, in early life, before ten days after birth, the developmental changes in the cell size would be quite similar to those in the Albino, which have been minutely described in part I, and that we may therefore apply to the Norway rat also the same developmental phases as were formerly applied to the Albino.

Morphological changes in the cytoplasmic and nuclear structures in the Norway rat cells are similar to those in the Albino, if the comparison is made at like ages, so that figures 3 and 4 in part I of this paper may be considered to represent Norway cells as well.

Briefly stated, in the case of the Norway rat, the maximum size of the pyramids in the lamina pyramidalis (in brains weighing 1.3 to 1.5 grams) is cell body 21 x 28 m and nucleus 20x21 n; values only slightly larger than those in the Albino. The final size of the ganglion cells in the lamina ganglionaris (in brains weighing 1.9 to 2.3 grams) is cell body 32x43 n and nucleus 26 X 27 n, which is much larger than the corresponding measurements for the Albino.

Nissl bodies are already seen in brains weighing 1.13 grams — the youngest case in my material — but these bodies assume their mature appearance first in brains weighing more than 1.6 grams.. As regards other developmental changes both in the cytoplasm and in the nucleus, the statements made for the Albino are all applicable to the Norway, if the comparison is made at like ages.

SUMMARY

1. In the full-grown Norway rat (Groups N XIX to N XXIII), the average size of the pyramids in the lamina pyramidalis is cell body 20 x 27 ii, nucleus 18x19 m, and the average size of the ganglion cells in the lamina ganglionaris is cell body 32 x 43 n, nucleus 26 x 27 At.

2. The cell body and the nucleus of the pyramids attain their maximum size (cell body 21 x 28 m, nucleus 20 x 21 m) in brains weighing 1.3 to 1.5 grams, and after that they slightly diminish

GROWTH OF THE CEREBRAL CORTEX 161

in size, but the internal structure matures progressively as the brain weight increases. The cell body and the nucleus of the ganglion cells increases in size continuously throughout life. The last entry for the nucleus of the ganglion cells is an exception to this statement.

3. As compared with the corresponding cells in the albino rat, the pyramids in the adult Norway rat (Groups N XIII to N XX) exceed those in the Albino in diameter on the average by 4 per cent and in volume by 12 per cent and the ganglion cells also exceed in diameter on the average by 7 per cent and in volume by 20 or more per cent.

4. The course of development and the morphological changes in the Norway cells are similar to those in the albino rat, if compared at like ages. At the same age, the Norway brain weight, less 18 per cent, is taken as equal to the brain weight of the Albino.

162 NAOKT SUGITA

LITERATURE CITED

Allen, Ezra 1916 Studies in cell division in the Albino rat (Mus norvegicus var. alba). II. Experiments on technique, with description of a method for demonstrating the cytological details of dividing cells in brain and testis. Anat. Rec, vol. 10, pp. 565-586.

Donaldson, H. H. 1915 The Rat. Memoirs of The Wistar Institute of Anatomy and Biology, no. 6.

Donaldson, H. H., and Hatai, S. 1911 A comparison of the Norway rat with the albino in respect to body length, brain weight, spinal cord weight and the percentage of water in both the brain and spinal cord. Jour. Comp. Neur., vol. 21, pp. 417-458.

IsENSCHMiD, Robert 1911 Zur Kenntnis der Grosshirnrinde der Maus. Abhandl. der Konigl. Preussischen Akad. d. Wissenschaften.

King, Helen Dean 1910 The effects of various fixatives on the brain of the albino rat, with an account of a method of preparing this material for a study of the cells in the cortex. Anat. Rec, vol. 4, pp. 213-244.

Stefanowska, Michelinb 1898 Evolution des cellules nerveuses corticales chez las souris apres la naissance. Annales de la Soc. Royale des Sciences nied. et naturelles de Bruxelles,, vol. 7.

SuGiTA, Naoki 1917 a Comparative studies on the growth of the cerebral cortex. II. On the increase in the thickness of the cerebral cortex during the postnatal growl-h of the brain. Albino rat. Jour. Oomp. Neur., vol. 28, no. 3. 1918 Comparative studies on the growth of the cerebral cortex.

III. On the size and shape of the cerebrum in the Norway rat (Mus norvegicus) and a comparison of these with the corresponding characters in the albino rat. Jour. Comp. Neur., vol. 29, no. 1.

1918 a Comparative studies on the growth of the cerebral cortex.

IV. On the thickness of the cerebral cortex of the Norway rat (Mus norvegicus) and a comparison of the same with the cortical thickness in the Albino. Jour. Comp. Neur., vol. 29, no. 1.

1918 b Comparative studies on the growth of the cerebral cortex.

V. Part I. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal sections of the albino rat brain, together with the changes in these characters according to the growth of the brain. Part II. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal section of the brain of the Norway rat (Mus norvegicus), compared with the corresponding data for the albino rat. Jour. Comp. Neur., vol. 29, no. 2.

author's abstract of this paper issued by the bibliographic service, march 30.

ON TACTILE RESPONSES OF THE DE-EYED HAMLET (EPINEPHELUS STRIATUS)i

W. J. CROZIER

1 . The observations herein discussed grew out of a first attempt to examine the physiology of excitation of the ' common chemical' sense in a teleost bearing a well-developed investment of scales. The work contemplated was rendered impossible, for reasons which will shortly appear, but the cause of the failure has a distinct bearing upon the original problem and a certain significance in several other directions as well.

Epinephelus striatus Bloch, the 'hamlet' or 'grouper,' was used in these experiments. The tests which were contemplated involved the local application of solutions to the skin of the hamlet, and it was necessary to employ fishes in which the chance of visual response had been eliminated. Recourse was had to the removal of the eyes rather than to the use of temporary blinding devices. Hamlets are exceedingly handy, and the removal of one or both eyes, usually while under chloretone anaesthesia, was followed, by quick recovery. Blinded individuals lived in the laboratory for more than four months.

In preliminary tests different regions of the surface of de-eyed hamlets were examined by applying to them from a pipette small volumes of acid and other solutions. Control experiments quickly demonstrated, however, that these fishes were reactive to the mere presence (or near approach) of the undischarged pipette, even when it contained only sea-water. A thoroughly cleaned glass rod, when carefully brought near a de-eyed hamlet, also induced responses of a deliberate and well-defined character.

A very pronounced degree of sensitivity is manifest in these responses, and the source of stimulation is rather precisely located

^ Contributions from the Bermuda Biological Station for Research. No. 86.

163

164 W. J. CROZIER

by the blind fish. When a clean glass rod is carefully and very slowly brought near one side of the head, say to within 4.5 or 5 cm. of the gill cover, the fish bends in the opposite direction and swims slowly backward; or it may back deliberately away for 10 or 15 cm., then abruptly turn away from the side stimulated and assume a position at right angles to that held before being stimulated. When one side of the caudal peduncle is stimulated in this way, the tail is caused to bend away from that side, and the fish swims forward and usually turns in a complete half-circle away from the area of activation.

Unblinded fishes, when not resting on the bottom, usually give somewhat similar responses, although rarely so if any region other than the anterior end is being 'stimulated' by the near approach of a glass rod. With de-eyed individuals the best results are obtained when the fish is quietly swimming or is stationary in mid-water. As noted by Jordan ('17, p. 447), the normal hamlet usually lies on the bottom of an aquarium, particularly in the angle between a wall and the base of the container. When in the latter position, the hamlet does not usually react by body movements to the close approach of a glass or metal rod, although eye movements and increased vibrations of the pectoral or other fins may show that the foreign object is seen and perhaps also sensed in some additional manner. It frequently happened that responses of the kind described were not obtained from totally blinded hamlets when they were in a similar position; that is, when they were resting in a corner of the aquarium.

This applies also to hamlets from which only one eye had been removed; animals so prepared characteristically seek a corner of the aquarium- — a dark corner, if such be available — and for long periods remain in a fixed position with the side

- The aquarium used in most of these experiments was that already described in Jordan's paper ('17). It had solid wooden ends and plane glass sides. In working with hamlets having one or both eyes functional the arrangements were such that the experimenter was screened from the fish, and the glass, or other, rod was suspended from above and moved about by an appropriate arrangement of strings.

TACTILE RESPONSES OF DE-EYED HAMLET 165

carrying the intact eye pressed against the confining wall. They seldom, if ever, moved in any way as the result of a solid object being brought near them on the hlmd side, although when actually touched on that side, however lightly, they made exceedingly violent escaping movements — much more vigorous movements, in fact, than are ordinarily evidenced by the normal seeing fish.

Whether or not the delicate form of sensitivity described for the completely blinded hamlet is present and actively functional in the unblinded animal cannot be decided from the facts so far given; but it can be shown that the responses in question are not the result of special sensory alterations determined by or during anaesthesia, since 1) different anaesthetics (chloroform, ether, chloretone) and various degrees of narcosis could be used for the de-eying operation without affecting the result in any way;

2) there is no discernible increase in sensitivity after a fish previously de-eyed has recovered from a second anaesthetization ;

3) a non-de-eyed fish does not give responses of the character under discussion after recovery from (chloretone) anaesthesia;

4) several hamlets from which the eyes were removed without anaesthesia, gave well-defined reactions of this nature.

Inasmuch as the reactions to the careful approximation of solid bodies were secured very shortly after the operation, and were evident almost to their maximal extent within twenty-four hours, it is doubtful if the inere absence of the eyes has produced this form of sensitivity; the following results, as well as the studies upon normal individuals, support such a conclusion:

a) When the eyes of a medium-sized hamlet were covered by a cap of black velvet, the fish became very restless (owing to mechanical irritation of the harness required to fasten the cap) ; but after about ten hours, good 'avoiding reactions' were obtained upon the careful approach of a glass rod, both at the snout and at the caudal peduncle.

b) In several hamlets the cornea of either eye, or of both eyes, was rendered opaque by searing with a hot iron. The fishes so treated behaved respectively as did those with one or both eyes removed.

166 W. J. CROZTER

The delicate sensitivity manifested in the responses of the bhnd hamlet upon the near approach of foreign objects is therefore not induced by the absence of the eyes or by procedures incidental to their removal; it is present in the normal seeing fish, although reactions to which it might give rise are largely inhibited through visual and coarse mechanical stimulations (touch). It is obvious that this form of irritability, if present but unrecognized, might lead to serious errors in the interpretation of different phases of behavior not only in the hamlet, but also in other, fishes where it may occur.

" 2. De-eyed hamlets, stationary in mid-water or slowly swimming, but not in contact with the bottom or walls of the aquarium, were found to show the following regional distribution of sensitivity to the gentle approach of the rounded end of a clean glass rod (3 mm. diameter) : tip of the snout, side of head, caudal peduncle, top of head, side of body (especially in the region covered by the pectoral fin w^^hen it is folded back on to the body), anterior edge of the erect spinous dorsal fin, soft dorsal fin, caudal fin (except near its distal extremity).

The parts are arranged in the foregoing list according to the vigor of the reactions induced. No well-defined responses could be secured from the ventral surface of the animal nor from the pectoral or pelvic fins. The nature of the response varies with the different regions of the animal; thus, the spinous dorsal was pulled down close to the body when its anterior edge was approached, while the soft dorsal responded by vibratory movements.

About twenty-five individuals were carefully studied to determine the distribution of this sensitivity to 'contact at a distance.' The critical tests were made in filtered 'outside' seawater (the circulating water of the laboratory being less alkaline than normal sea-water), and the conditions were so arranged that no shadows from the body of the experimenter or from the glass rod fell upon the surface of the fish. These tests were made upon single isolated fishes in non-running water.

Rods or wires of a number of different materials were found to induce reactions of this type. In all cases the rods were well

TACTILE RESPONSES OF DE-EYED HAMLET 167

cleaned; metal rods or wires were brightly polished and the strips of wood were freshly planed. Tests were made with rods immediately after cleaning and also when they had lain in seawater for an hour or more. The substances used were:

Metals: copper, platinum, gold, zinc, cadmium, aluminum, wrought iron, steel, galvanized iron, and brass.

Woods: 'cedar,' spruce, oak, elm and cypress.

Miscellaneous: glass, hard rubber, sealing-wax, soft rubber (red, white, and black tubing), porcelain, hard paraffin, sandstone, and compressed carbon.

The great variety of materials which induced the same response is sufficient to show that the process of stimulation did not depend upon the diffusion of chemical excitants nor (in the case of the metals) upon any 'action at a distance,' either primarily electrical or through the escape of charged atoms of metal (cf. Mathews, '07). The cadmium stick and the wires of platinum used in the tests were particularly pure, and no difference in the response they induced could be detected after they had been covered with neutral paraffin. The reactions are somewhat variable, and it is conceivable that some substance may stimulate in this fashion (i.e., 'chemically') more than others, but I could find no evidence of it in the hamlet. This point was tested with some care, because I had learned from Prof. G. H. Parker of reactions found by him with the catfish when approached by metal rods. Nor could I find anything of this sort in Amphioxus, Balanoglossus, sea-anemones, crabs (blinded), the 'rhinophores' of nudibranchs, or several teleosts that were examined.

Rods of brass, iron, glass, or wood of different diameters and shapes were then tried. Fishes of fairly uniform size (about 30 cm. length) were used in comparative experiments. To avoid, as far as possible, communicating undesired trembling movements to the rods, and thus to the water, the rods were in many tests clamped firmly in the middle of the aquariuni and the behavior of the blinded hamlet when approaching them during slow swimming movements was compared witlj the result when a rod was carefully brought near a part of the body. The result was in

168 W. J. CROZIER

either case the same; when slowly swimming the de-eyed hamlet will most often neatly avoid contact with a rod or wire situated in its path, but more successfully if the end or edge of the rod presents a sharp corner. Similarly, in many cases, the fish is somewhat better stimulated by a thin wire (less than 1 mm. in diameter) than by a thicker one and by a rod of square cross section than by one of similar size (several centimeters in diameter) but with a smoothly rounded end and circular cross section.

The inference from these tests is, unavoidably, that mechanical deformations in the water, of a somewhat irregular character, are the means of stimulation. It was shown by appropriate elimination experiments that the nostrils and lateral-line organs could not be concerned, and this is further made obvious from a consideration of the local nature and manner of distribution of these reactions over the body of the fish.^

The mode of excitation in these reactions is in certain particulars significantly different from that in some reactions which have previously been attributed to tactile excitation of the skin in teleosts (cf. Parker, '04, pp. 61, 62; Jordan, '17). A current from a pipette or ripples at the water surface frequently failed to induce any perceptible reaction in a de-eyed hamlet, although immediately after this, or immediately before, a slender rod or wire slowly brought to within 5 cm. of the snout or caudal peduncle led to well-defined reactions. Moreover, it was often possible to get good reactions to a thin rod in water much disturbed by a current of relatively large volume.

The snout and lips of the hamlet were the most sensitive regions of the animal's surface. There is thus a general parallelism between the distribution of this delicate tactile sensitivity and that of skin sensitivity to currents, as described by Jordan ('17). Whether or not this indicates the actvity of the tactile corpuscles in the reactions herein discussed, I am not sure; but I suspect that the tactile corpuscles may not be involved, although con ^ It may be suggested that the reactions of Amoebae to insoluble substances, as described by Schaeffer ('16), are possibly due to some such form of irritability as that herein considered. Certain peculiar phenomena obtainable with human erythrocytes (Oliver, '14; Kite) are also suggestive in this connection.

TACTILE RESPONSES OF DE-EYED HAMLET 169

elusive evidence for this belief cannot be adduced. The higher sensitivity of the anterior end of the de-eyed hamlet was not occasioned by the presence of freshly exposed tissue surfaces in the orbits or by other injuries, since in several cases the animals were kept in aquaria for more than four months, long after the orbit surfaces had cleanly healed, and their reactions were as distinct as those of recently de-eyed fishes.

The relatively acute sensitivity of the region behind each pectoral fin, as judged by the reactions obtained when it was approached by a rod, is probably a secondary condition, due to the fact that the pectoral fins are usually in slight motion, creating in the water waves which impinge upon tl^se surfaces; any disturbance of these wave fronts or fin currents would result in a greater stimulus than that afforded by the near approach of a rod or wire to a stationary part.

3. I have ventured to describe these tactile reactions of the de-eyed hamlet at some length, because the fine, 'epicritic' nature of the sensitivity evidenced toward minute mechanical disturbances in the water is of particular use for the purposes of certain critical experiments regarding chemical stimulation of the skin of fishes. It will be observed that crude tests made by applying solutions from a ffipette to the skin of Epinephelus would be quite pointless, since the blinded fish reacts with precision to the presence of the undischarged pipette. The degree of sensitivity in these delicate tactile reactions is nevertheless rather definitely fixed at a uniform level, as seen in the more than twenty-five individuals I have examined. The speed, vigor, and amplitude of these reactions give them a perfectly definite character. It is conceivable that this tactile sensitivity might be enhanced or diminished under various conditions and that such variations would be reflected in the behavior of the de-eyed fishes, and that, in fact, a good opportunity would be offered for discovering the way in which tactile terminals may be influenced by such treatment of the skin as is involved in the local application of chemical excitants. If, as is supposed by Coghill ('14, p. 197; '16, p. 302), those responses of fishes and amphibians usually regarded as being initiated through excitation of ter

170 W. J. CROZIER

minals representing a 'common chemical sense/ are in realitj'^ due to the heterologous activation of tactile and pain terminals/ owing to destruction of the epithelium, then it would be expected that the local application of irritants to the skin of the hamlet would produce one of two effects; either tactile sensitivity would be noticeably increased immediately thereafter or, following relatively severe treatment, it would be found more difficult to bring about tactile activation. In the former case it might be held that excitants for the 'common chemical' sense are capable of acting upon tactile receptors in a sensory way.

In testing this matter, my experiments dealt mainly with the areas of skin on QJther side of the caudal peduncle, although other regions were also examined, notably, the lips and giU-covers.

In different individuals these areas were treated with solutions of cocaine hydrochloride in sea-water by painting the surface in question (held out of water) with a brush. The dermal chromatopores in the region cocainized quickly contract and remain contracted for some hours. The area treated is sharply outlined by the blanching of the skin. The narcotized area is thus clearly delimited for reference in stimulation trials.

Even slight cocainization causes a complete suppression of the sensitivity to rods or wires, as well* as to water currents; slightly stronger narcosis obliterates all responses to touch. Even then, however, the anaesthetized surface is fully active in the reception of stimulation from acid and alkaline solutions (HCl, NaOH, NH4OH, n/20-n/40) or from dilute solutions of quinine. The sensitivity to delicate mechanical stimulation in these experiments returns with equal rapidity whether or not the narcotized area has been stimulated chemically while under anaesthesia.

The hamlet, normal or de-eyed, reacts to local treatment with n/20 NaOH or NH4OH on the caudal peduncle after the spinal cord has been transected, but this operation obliterates the sensitivit}^ to minute mechanical disturbances at all levels posterior to the cut and decreases the amplitude of responses of this nature in other regions.

■* A view suggested also hy Watson ('14, pp. 419) and apparentfj^ accepted in some degree by Herrick ('16, pp. 85).

TACTILE RESPONSES OF DE-EYED HAMLET 171

By several stimulations in rapid succession the vigor of the response elicited upon the near approach of a glass rod may be to some extent heightened. Such reactions are never so vigorous as those called forth by acid or alkali. If, however, tactile stimulation by this means be induced immediately after relatively severe chemical irritation (n/10 HCl from apippette), it is found either that the local irritability is quite unaffected or that it is slightly decreased. With weaker acid, inducing, nevertheless, very vigorous reactions, no effect could be detected upon subsequent excitability by the near presence of glass rods or wires.

The results of the test thus briefly outlined are uniformly in agreement with the idea that (within physiological limits) the excitation of the 'common chemical sense' has nothing to do with tactile receptors or with the destruction of the epithelium, since the delicate form of 'touch at a distance' employed in the de-eyed hamlet shows no specific effects of a sort otherwise to be expected when the receptive areas of this sense are bathed with chemical excitants. These results make it impossible to suppose that acid, for example, could disorganize the skin (as suggested by Coghill) sufficiently to induce violent painful excitation and yet at the same time leave sensitivity to minute mechanical disturbances practically unaffected.

And if acid acted directly upon tactile receptors, it would be expected that organs of delicate tactile receptivity would behave toward subsequent mechanical activation as if they had recently been activated; as previously described, this is apparently not the case. It might be objected that the source of stimulation could not, in the 'tactile' experiments with wires and rods, be localized with sufficient precision for critical use. Yet this would be incorrect, as could very nicely be shown in tests made upon small narcotized areas of the skin. Regions (on the caudal peduncle) not more than 2 cm. in diameter were painted with cocaine, and when the pale anaesthetized part was approached with the end of a thin rod, no reactions followed, although similar spots 3 cm. away were of fully normal sensitivity.

This result confirms the conclusion which I supported in a previous paper ('16), to which Coghill ('16) has made further and (it

172 W. J. CROZIER

seems to me) quite miwarranted objection. According to a conception first formally advanced by Botezat ('10) and later applied by Parker ('12) to the general chemical irritability of moist surfaces in vertebrates, the stimulation of epithelial free nerve terminals is accomplished secondarily through the activity of substances diffusing from the more external epithelial cells (some of which may be supposed to be in a special receptive state, although this is not necessary) to deeper parts. There is obviously no necessity that the nerve terminals concerned be situated near the surface immediately exposed to the activating agent. The cells primarily activated by acid or alkali in the 'common chemical sense' experiments are undoubtedly those of the very outermost layer of the skin. A study of the conditions of chemical activation in primary receptors (of the earthworm) shows, or seems to show, that a chemical reaction occurs between the activating agent and some receptor constituent.^

This means that the acid or other agent stimulates after union with, or penetration of, the surface of the superficial cells. The acid or other substance does not act directly upon deeper layers of the skin, for the good and sufficient reason that the stimulation time is utterly inadequate for any such process, even though the changed condition in the cell primarily affected can obviously be transmitted from cell to cell through the whole depth of the epidermis in a very brief time.^ The fact that one small area of the skin may be excited repeatedly by acid or by alkali shows that no destructive action is wrought by these excitants (within reasonable limits of concentration).

It is becoming more and more necessary to recognize that receptor organs depend for their differential irritability upon the possession of specific substances which enter into excitation reactions. There is reason to suppose that in mechanical stimulation surfaces (intracellular, intercellular, or both) are tempo ^ Some of the results of this investigation are in course of publication.

^ This primary effect may or may not be an increase in cell permeability, but it undoubtedly does involve an alteration in the relations between ions at the surfaces of the stimulated cells; hence the violent stimulating effect of distilled water under certain circumstances, as Loeb long ago found in the case of the frog's foot.

TACTILE RESPONSES OF DE-EYED HAMLET 173

rarily broken down, to a certain extent, so that substances normally kept apart are free to intermix and react. There is no reason to expect that the products of the chemical activation of epithelial cells should be able to bring about a specific action upon tactile nerve endings or upon the specialized accessory end organs of the tactile sense. Tactile organs, 'corpuscles,' or what not may obviously be (and in fact frequently are) situated at some distance from the outer epithelial surface; it is probable, however, that the 'epicritic' form of irritability described in the hamlet depends upon very superficial structures; hence their particular value for the present research.

These considerations may enable one to see why it w^ould be somewhat surprising to find tactile organs in fishes capable of being normally excited by acids, for example.

It is easily seen that differential anaesthesia is, by itself, in many cases a poor criterion of sensory differentiation ; and yet, in the case of cocaine, when the results obtained by this method agree perfectly with other and quite independent methods of analysis, the results must perforce be accepted. In the present case it is rendered probable that the production of stimulation by chemical irritants applied to the general surface of Epinephelws has nothing to do with tactile receptors, and that the obliteration of tactile ('epicritic') sensitivity by cocaine is not an 'artifact' due to the specifically more intense action of the chemical irritants. Even in coelenterates there are indications that irritant chemicals and mechanical agencies respectively act in a sensory way upon differentiated receptors having diverse internal connections (Parker, '17), and the present observations confirm the idea that these agencies have modes of action in lower vertebrates as separate as they are in man.

4. Responses similar to those described for the de-eyed hamlet are exhibited by the normally blind cave fishes, according to Eigenmann (cited by Whitman, '99, p. 303). The parallehsm is striking, since in both cases the direction from which a rod is being brought near is accurately located, while vibrations of a coarser order may not be responded to. In^the blind fishes, however, this form of sensitivity is said to be more active in younger individuals than in adults.

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 2

174 W. J. CROZIER

Inasmuch as tactile sensitivity of a very highly developed character is present in the hamlet possessing well-developed functional eyes, there is no reason to believe that a similar superior degree of tactile irritability has been developed in the blind cave fishes as the result of their lack of vision."

Concerning the function of this sense in Epinephelus, it may be suggested that it is useful at night or when the fish is maneuvering in darkened crannies of the 'coral reefs.'

SUMMARY

The de-eyed hamlet (Epinephelus striatus) gives well-defined reactions to the near approach of solid bodies. In the seeing fish this form of sensitivity is present, but motor effects which it might induce are almost completely inhibited. Mechanical deformations in the water of very minute amplitude and of a somewhat irregular nature are the source of stimulation in these responses, which cannot be attributed to chemical or to electrical disturbances. The presence of this exceedingly delicate form of sensitivity, generally distributed over the surface of the fish and leading to deliberate reactions of a well-defined character, has been used to discover any influence of chemical excitants, locally applied, upon the end organs of tactile sensitivity. Although the existence of this 'epicritic' form of irritabilit}^ interferes with any direct study of the mode of excitation in 'common chemical sense' reactions, it can nevertheless be shown, with its aid, that the generally distributed 'common chemical' irritability of this fish does not involve tactile receptors. Since the hamlet with well-developed eyes exhibits a high degree of tactile discrimination, such as has been described for blind cave fishes, — although the existence of this sensitivity would be quite overlooked unless

^ It should be added that after living in the laboratory for more than four months after the removal of the eyes, three hamlets were cai-efuUy compared with several others recently de-eyed as regards their comparative 'tactile' irritability; no differences could be detected. Hence continued lack of vision does not lead to an increased development of the hamlet's 'epicritic' tactile irritability.

TACTILE RESPONSES OF DE-EYED HAMLET 175

blinded animals were studied, — it is unnecessary to suppose that sensory structures appropriate to this type of irritability have been determined either by blindness or by life in caves. Agar's Island. Bermuda.

LITERATURE CITED

BoTEZAT, E. 1910 tJber Sinnesdriisenzellen und die Funktion von Sinnesap paraten. Anat. Anz., Bd. 37, pp. 513-530. CoGHiLL, G. E. 1914 Correlated anatomical and physiological studies of the

growth of the nervous system of Amphibia. I. The afferent system

of the trunk of Amblystoma. .Jour. Comp. Neur., vol. 24, pp. 161 233.

1916 II. The afferent system of the head of Amblystoma. Ibid., vol. 26, pp. 247-340.

Crozier, W. J. 1916 Regarding the existence of the 'common chemical sense'

in vertebrates. Ibid., vol. 26, pp. 1-8. Herrick, C. J. 1916 An introduction to neurology. Phila., 355 pp. Jordan, H. 1917 Rheotropic responses of Epinephelus striatus Bloch. Amer.

Jour. Physiol., vol. 43, pp. 438-454. Mathews, A. P. 1907 An apparent pharmacological 'action at a distance' by

metals and metalloids. Ibid., vol. 18, pp. 39-46. Oliver, W. W. 1914 The crenation and flagellation of human erythrocytes.

Science, N. S., vol. 40, pp. 645-648. OsTERHouT, W. J. V. 1916 The nature of mechanical stimulation. Proc. Nat.

Acad. Sci., vol. 2, pp. 237-239. Parker, S. H. 1904 Hearing and allied senses in fishes. Bull. U. S. Fish.

Comm., vol. 22 (for 1902), pp. 45-64.

1912 The relation of smell, taste, and the common chemical sense

in vertebrates. Jour. Acad. Nat. Sci., Phila., Ser. 2, vol. 15, pp. 221 234.

1917 Nervous transmission in the actinians. Jour. Exp. Zool., vol. 22, pp. 87-94.

ScHAEFFER, A. A. 1916 On the behavior of Ameba toward fragments of glass and carbon and other indigestible substances, and toward some very soluble substances. Biol. Bull., vol. 31, pp. 303-326.

Watson, J. B. 1914 Behavior: an introduction to comparative psychology. New York, xii + 439 pp., ills.

Whitman, C. O. 1899 Animal behavior. Biol. Lect., Mar. Biol. Lab., Woods Hole (1898). Boston, pp. 285-338.

author's abstract of this paper issued bt the bibliographic service, march 30

COMPARATIVE STUDIES ON THE GROWTH OF THE CEREBRAL CORTEX

VII. ON THE INFLUENCE OF STARVATION AT AN EARLY AGE UPON THE DEVELOPMENT OF THE CEREBRAL CORTEX. ALBINO RAT

NAOKI SUGITA

From The Wistar Institute of Anatomy and Biology

TWO CHARTS

1. INTRODUCTION

Investigations on the influence of partial or complete starvation upon the growth of the body under various conditions have been made by many authors, and it has long been known that of all the organs the brain is least affected in weight by underfeeding while, in younger animals in active growth, the brain weight may even increase during severe underfeeding. These facts were early observed by Chossat ('43) in pigeons, Falck ('54) in dogs and Voit ('66) in cats, later by Bechterew ('95) in kittens and puppies and Lassarew ('97) in guinea-pigs, and recently by Hatai ('04, '08, '15), Donaldson ('11), Jackson ('15 a, '15 b), and others working in the albino rat. Jackson made experiments with complete and partial starvation on adult albino rats and also held the young albino rats at constant body weight for a considerable period by partial underfeeding, and in all his experiments the brain was found to be only slightly affected in weight. Hatai underfed young rats so as to cause a reduction of 30 per cent in total body weight, while the average loss in brain weight was only 5 per cent. According to Donaldson's experiments on the young albino rats (thirty days old) under moderate underfeeding for three weeks, it was found that the underfed are on the average 41.2 per cent less in body weight than the controls and nevertheless only 7.7 per cent less in brain weight.

177

THE JOURNAL OF COJIPARATIVE NEUROLOGY, VOL. 29, NO. 3

JUNE. 1018

178 NAOKI SUGITA

According to lYiy previous studies on the normal development of the cerebral cortex during the period of most active growth (Sugita, '17, '17 a, '18 a, '18 b, '18 c), it was found that the growth of the cortex is precocious and that its elementary organization (that is, the cortical thickness, the cortical cell number and cell size, etc.) is nearly completed at the time of weaning, when the albino rat is twenty days of age. The investigations by the several authors cited above were, however, made mostly on animals which were already weaned, because, of course, feeding experiments necessitate a strict food control. But at this stage (after weaning), the elementary organization of the cerebral cortex is already completed. For my object, which was to determine the effect of starvation on the early development of the cerebral cortex, it was necessary to use animals in which the growth of the cerebral cortex was still in active progress and to note the influence upon the organization of the cortex of longer and shorter periods of inadequate feeding.

For this it is necessary to use the very young animals, still dependent on the mother. During this period the growth impulse in the brain is especially strong and the results of underfeeding are somewhat peculiar, as the brain weight may even increase under severe underfeeding. In complete starvation, growth is stopped and the brain weight remains constant. Thus, von Bechterew ('95) studied on new-born kittens and puppies the influence of complete starvation upon the brain w^eight. His results were that the brain weight, at the time of death after three or four days of starvation, was like the initial weight of the organ at birth. The brain had not grown, but also it had not lost in weight.

By applying severe starvation to the albino rat immediately after birth, it has been my object in the present study to obtain answers to the following questions:

1. How far will the growth of the body and of the brain be arrested?

2. Will the normal relation between body weight, body length, and tail length be modified?

GROWTH OF THE CEREBRAL CORTEX 179

3. What will be the relation between body weight and brain weight in the underfed rats?

4. How far will the size and shape of the cerebrum be influenced?

5. Will the thickness of the cortex of the stunted rats be different from that of the standard?

6. How far will the Volume of the cerebral cortex be modified?

7. Will the number of the cortical cells increase normally according to age?

8. Will the development in the size of the nerve cells be influenced by starvation?

9. What will be the effect of the starvation on the percentage of water and on the alcohol extractives?

2. THE TEST ANIMALS

After several preliminary tests on producing underfed young, I adopted the following three procedures, which are fairly reliable:

I. Separation of the young from the nursing mother for a maximum period each day.

II. Entrusting one mother with an excessive number of young and thus reducing the amount of milk available for each of the young.

III. Underfeeding the nursing mother and thus reducing the quantity of milk secreted.

I treated five litters by the first method (Series I), two litters by the second method (Series II), and one litter by the third method (Series III). The detailed records of these experiments are on file at The Wistar Institute of Anatomy and Biology. All the material, consisting of forty-six test individuals and fourteen controls, from the above eight litters, was supplied from the rat colony at The Wistar Institute. They are all from mothers of standard size which were kept throughout the experiment under good sanitary conditions.

This study was carried on from October, 1916 to July, 1917, at The Wistar Institute of Anatomy and Biology.

180 ■ NAOKI SUGITA

3. MATERIAL

Series I (Litters A, B, C, D, and E, table 1)

Procedure. In each litter, half of the young were selected for the experiment and marked with hectograph ink on the back and the remaining individuals were used as the controls. The young under experiment were taken away from 'the mother each day and kept packed in cotton in a warm place, but without any food or water, for the time which had been determined. Table 1 contains the records of the number of hours during which each test individual in this series was isolated each day.

Litter A {horn October 16, 1916) was composed of nine young. Five (c, a, d, f, and h) were subjected to experiment and were separated from the mother daily beginning on the very day of birth, the f oodless interval being increased day by day, as recorded in table 1. Sundays were excluded from any experimentation. The duration of starvation, daily and total, and the age at which the animals were killed is recorded also in table 1. Four controls (b, e, g, and i) were also killed one by one at the same' ages as the test animals. The total hours of isolation, the average per day, and the percentage of hours isolated during the total life of the individual in hours, are given in the lower part of the table. As the young are not fed continuously, even when they were with the mother, this percentage will but roughly indicate the grade of underfeeding to which the young were subjected. They were killed for examination at the ages of 3, 4, 9, 11, and 15 days (see X in table 1).

Litter B {born October 15, 1916) consisted of ten young. Five (a, c, e, f and i) were separated daily from their mother, as in the case of Litter A, and the remaining young (b, d, g, h, and j) were used as controls. The experiment was begun at the age of one day in Litter B, a day later than in the case of Litter A. They were killed for examination at the ages of 4, 8, 11, 12, and 19 days.

Litter A and B represent groups in which mild starvation was instituted from a very early age.

Litter C {born October 18, 1916) was composed of seven young, of which four (a, c, d, and f) were used for experiment and three

GROWTH OF THE CEREBRAL CORTEX 181

(b, e, and g) for control. The experiment was begun five days after birth. One test rat (f) and one control (g) were killed by the mother. For the first three days mild starvation was tried, and then, from the age of nine days, severe starvation was instituted. They were killed for examination at the ages of '15, 17, and 28 days.

Litter D {horn October 23, 1916) consisted initially of eight young, of which five (a, c, d, e, and g) were used for experiment and three (b, f, and h) for control. One underfed (g) and one control (h) were killed by the mother. In this litter severe starvation was begun at the age of three days. The animals were killed at the ages of 9, 10, 16, and 18 days.

Litter E {horn Novernher 4, 1916\ was composed of eight rats, of which six (a, b, c, d, g, and h) were selected for experiment and two (e and f) for control. Severe starvation with some intervals of feeding was begun at the age of three days. In this litter pairs of test rats of the same age were killed for examination (on the 7th, 10th, and 17th days of the experiment) to determine individual variations.

Litters D and E represent groups in which relatively severe starvation was begun at an early age.

Series II {Litters F and H)

Procedure. In this series one nursing mother was placed in charge of an excessive number of young. The results were not very good, because some relatively lucky or strong ones always got more than their share of milk, while the others were in a condition of severe underfeeding.

Litter F {horn Octoher 15, 1916). To a young small primipara, which had just given birth to ten young, were entrusted ten more young from two other litters which had been born on the same day. Unhappily, the young from three different litters were not separately marked. The rate of growth among them was later found to be unequal, owing probably partly to litter characteristics and partly to the inequality of the milk ration. Individuals were selected arbitrarily and killed for examination at intervals of one to three days (at the ages of 11, 14, 17, 19,

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20, 23, 24, 26, 30, and 40 days). Those killed were replaced by individuals of like age from other litters, so as to keep the number in this litter always above thirteen. After twenty days, the mother was removed and the young fed with a small amount of ordinary food. The last eight young, which survived beyond the age of forty days, were rejected as too old for the purpose of this study.

Litter H {born January 2, 1917). A mother having just given birth to eight young was entrusted with nine more young from another litter which had been born on the same day. The underfed young of this litter were all employed for the study on the percentage of water and for the histological study of myelination in the brain and not included in the study of the cerebral cortex.

Series III {Litter G)

Litter G (born October 23, 1916). In this series a nursing mother was severely underfed immediately after the parturition. This litter consisted of eleven young. Only a fraction (one-tenth to one-twentieth) of the ordinary diet with unlimited water was supplied daily to the mother. She was found to lose slowly in body weight day by day. The amount of milk was consequently much reduced, but not completely stopped, as could be determined by examining daily the stomach contents of the young. By this method I was able to get a series of young which were very poorly developed. The young were killed for examination at the ages of 8, 10, 11, 12, 15, 16, 18, 22, and 25 days.

Table 2 contains the observed body weight and brain weight of the young in Litters F, G, and H, when examined, for a comparison with table 1.

•4. BODY WEIGHT, BODY LENGTH AND TAIL LENGTH

Table 3a (not published, because of its complexity, but on file at The Wistar Institute), gives for each individual in this study the sex, age, observed body length, tail length, and brain weight. The standard tail length and the standard brain weight for the observed body length were also entered for comparison, the

GROWTH OF THE CEREBRAL CORTEX

185

TABLE 2

Showing for each test individual in Series II and III (Litters F, G, and H) the sex, age, and body and brain loeights, at time of examination

LITTER (series II AND III)

SEX

AGE OF KILLING

BODY WEIGHT

BRAIN WEIGHT

days

grams •

grains

Fa

m

11

8.5

0.709

b

f

14

9.8

•0.954

c

f

17

13.5

1.106

d

f

19

13.3

1.218 •

e

m

20

12.4

1.148

f

m

23

11.2

1.230

g

f

• 23

14.2

1.224

h

m

24

13.5

1.170

i

f

26

17.0

1.197

J

f

30

24.2

1.219

k

m

30

18.7

1.222

1

f

40

40.0

1.310

Ga

m

8

7.5

0.679

b

f

8

7.4

0.703

c

f

10

10.3

0.864

d

m

11

9.8

0.929

e

f

12

8.8

0.907

f

m

15

7.3

0.881

g

in

16

7.3

0.948

h

m

18

9.6

1.119

i

f

22

12.2

1.110

J

m

25

17.2

1.234

Ha

f

13

8.8

0.880

b

f

17

10.8

1.024

c

f

23

14.7

1.135

d •

f

28

17.2

1.166

e

m

32

20.0

1.215

f

f

37

19.3

1.101

g

m

43

21.1

1.295

values having been calculated for each individual by the use of formulas given in 'The Rat' (Donaldson, '15). Here the body length was chosen as the basis for comparison, because the increase in body length has proved less variable than body weight. Table 3 was condensed from the original complete table (table 3a) by dividing the individuals, the tests, and controls within each litter into two groups, according to the observed brain

186 NAOKI SUGITA

weight and taking averages for each group. Group I consists of those which have brains weighing less than 1.0 gram and presumably still in the first phases of cortical development (Sugita, '17 a) and Group II those which have brains weighing more than 1.0 gram and probably in the second or third phase of cortical development. So, one litter in Series I was divided into four groups, the tests having brain weights less than 1.0 gram (T. I), the tests having brain weights more than 1.0 gram (T. II), the controls having brain weights less than 1.0 gram (C. I) and the controls having brain weights more than 1.0 gram (C. II). This grouping prevails throughout all condensed tables (tables 3 to 13, 16 and 17) published in this paper. The average values were all obtained according to individual measurements, and the average standard values were also obtained by averaging from the full tables, which give the individual cases. As the standard values were not based on the average measurements given in the condensed tables, those standards given in the condensed tables sometimes deviate slightly from the standard values which would be directly obtained for the given average measurements.

On comparing, in table 3, the observed measurements with the corresponding standards, no significant difference between them has been detected, either in the underfed or in the controls. Only the body weight in the underfed is slightly lower as compared with the standard for the same body length, but it amounts to no more than 8 per cent.

This comparison indicates that, though the underfed young show a considerable retardation in total growth according to age (see table 4), yet the relation between the body and the tail lengths and the body weight is but little affected, at least during the early period of active growth. So the only marked difference between the underfed and the controls of the same body length or body weight would be the age, if their brain weights are disregarded. The effect on the brain weight will be discussed in the next chapter.

GROWTH OF THE CEREBRAL CORTEX

187

TABLE 3

Giving for each litter group in this sttidy the average age, body length, tail length, and body weight, the last two compared with the corresponding standard measurements for the observed body length, calculated according to sex by the use of formulas given in 'The Rat' 'Donaldson, '15). The general averages for the test and the control groups are given at the foot of the table. T = test, C = control.

TEST CONTROL

SEX

AVERAGE AGE

BODY

LENGTH

TAIL LENGTH

BODY WEIGHT

SERIES, LITTER AND GROUP

Observed

standard

aocord ina to

body

length

Observed

Standard according to bodylength

Series 1

A c, a, d, f

h

b, e, g i

T. I T. II

C. I C. II

1 m, 3 f 1 f

3 m 1 f

days

715

8 17

ni m .

56.3 74.0

66.7 96.0

mm.

26.5 48.0

31.7 62.0

mm. 26.3 47 .0

37.0

71.0

grams

7.2

13.9

11.7 30.1

grams 7.1

13.9

10.2 26.3

Series I

B a, c, e, f

i

b, d g, h, j

T. I T. II

C. I C. II

3 m, 1 f 1 m

2f 3f

919

6

18

59.8 75.0

57.0 86.3

27.8 50.0

25.5 53.3

29.8 46.0

27.5 61 3

7.3 12.7

7.1 20.5

7.9 13.6

7.0 20.3

Series I C a, c, d

b, e

T. II C. II

2 m, 1 f 2 f

20 22 —

82.0 98.5

51.7 71.5

54.3 73.5

15.1

27.6

17.5 29.4

Series I

D a, c, d

e

b

f

T. I T. II

C. I C. II

1 m, 2 f 1 m

1 m 1 m

12 18

9 22

61.0

78.0

69.0 91.0

39.0 54.0

39.0 65.0

31.7 49.0

40.0 63.0

6.9 13.0

11.2 24.0

8.2 15.0

1.0

21.9

Series I

E a, b, c, d

g, h

e, f

T. I T. II

C. II

3 m, 1 f 2 f

1 m, 1 f

1220

17

65.8 82.0

87.0

35.0 58.0

56.5

36.8 56.0

60.0

9.7 16.2

21.6

9.9 17.9

0.4

Series II

Fa, b

c-1

T. I T. II

1 m, I'f 4 m, 6 f

13 25+

63.5 83.9

33.0 61.5

34.5 57.1

9.2 18.1

9.1 19.4

188

NAOKI SUGITA

TABLE Z— Continued

TEST CONTROL

SEX

AVE RAGE AGE

BODY LENGTH

TAIL LENGTH

BODY WEIGHT

SERIES, LITTER AND GROUP

Ob

Standard accord

Ob

Stsadard accord

served

ing to body length

served

ing to body length

days

mm.

7)1 m.

mm.

grams

grams

Series III

Ga-g

T.

I

4 m, 3 f

11 +

63.0

32.9

33.7

8.3

8.8

h-j

T.

II

2m, If

22

7i.O

48.7

46.7

13.0

14.1

Series II

H a

T.

I

1 f

13

63.0

33.0

34.7

8.8

9.

b-g

T.

II

2 m, 4 f

30

81.7

64.0

53.8

17.2

17.1

Average 1

T.

I

11

61.8

32.5

32.5

8.2

8.6

.(Series I-III)J

T.

II

21+

79.0

54.5

51.2

14.9

16.1

Average )

C.

I

8

64.2

32.1

34.8

10.0

9.4

(Series I)/

C.

II

19+

91.8

61.7

65.8

24.8

23.7

5. BODY WEIGHT AND BRAIN WEIGHT

Table 4 was condensed from table 4 a (unpublished), which gives data for each individual in this study, and shows for each group, in the three series, the sexes, average age, average duration of starvation (denoted by percentage value of the hours of isolation), and the observed body and brain weights, accompanied by the average values for the group of the individual standard weights, for the same ages, and of the individual standard brain weights for the same ages and for the same body weights. For the calculation of the standard values for each individual the sex was regarded, because in body and brain weights the sex difference is clear ('The Rat,' Donaldson, '15). The average differences of the observed values from the standards are given for each group in percentage, the standards being taken, respectively, as the norms for comparison.

A glance at the table reveals three differences which are clearly marked :

1. The underfed rats have, as a rule, body weights considerably less than the standard values for the same age.

GROWTH OF THE CEREBRAL CORTEX 189

2. The underfed rats have brain weights somewhat less than the standard values for the same age.

3. The underfed rats have brain weights mar" edly higher than the standard values for their observed body weight.

It was already noted in the introduction that the central nervous system as represented by the brain suffers little or no loss of initial weight even in the case of severe starvation. In my series-T-underfeeding of the albino rat at an early age — the body weight of the rats stunted by starvation, as compared with the standards for the same age, were deficient (on the average by litters, table 4) by from 19 to 44 per cent. On the other hand, the brain weights were less than the standards for the same age by from 4 to 12 per cent (for litters, table 4, but by from 3 to 17 per cent for individuals, table 4 a), while for the same body weights they were from 15 to 29 per cent (for litters, table 4, but up to 65 per cent for individuals, table 4 a) above the standard values.

Considering together all the five litters (A to E) of Series I, in which the young were starved by separating them at an early age from the mother daily, it appears that the underfed rats at the end of the first twenty days after birth (during the suckling period) are about 29 per cent (average of A, T. I and II, B, T. I and II, C, T. II, D, T. I and II, and E, T. I and II) behind the standards in body weight, while they are only 8 per cent (averge of the above-cited cases) behind in the brain weight. In Series II and III, in both of which the young were subjected to early and continuous underfeeding, increasing in intensity, by the method of reducing the ration of milk, but without removal from the nest, the underfed young have shown a slightly better development in brain weight (in relation to body weight), the average being also 8 per cent (average of F, T. I and II, G, T. I and II, and H, T. I and II) less than the standard for the same age, while the body weight is on the average as much as 39 per cent (average of the above-cited cases) below the standard value. Whether removing the young from the nest increases the relative effect of underfeeding on the brain, as these results suggest, can be determined only by experiments with that question as the main point in view.

190 NAOKI SUGITA

In connection with the underfeeding, as practiced in Series I, some interesting results of overfeeding have been noticed in the control animals ; overfeeding having taken place in the case of the controls of Litters A to E on account of the periodic isolation of a number of the members of the litter. The controls have shown generally, as seen in table 4 a (unpublished) and also in table 4, some excess in body and brain weights, as compared with the standard values for the same age. The excess in body weight is on the average 19 per cent (average of A, C. I and II, B, C. I and II, C, C. II, D, C. I and II, and E, C. II), while the brain weight is on the average 6 per cent (average of the above-cited cases) higher than the standard for the same age and 2 per cent higher than the standard for the same body weight. Thus, by moderate overfeeding, the growth in body weight is definitely accelerated and, at the same time, the growth in brain weight is also accelerated, nearly in proportion to the increase in body weight.

If the observed brain weights are compared with the standard brain weights for the observed body weight, it is clearly seen that the observed brain weights are higher than the standard by 24 per cent (average of all eight litters T. groups only). Of course, the younger the individual, the higher is the percentage, because the standard brain weight is smaller in the young animals and they are not increasing in direct proportion to the body weight, but nearly as the logarithm of the latter value. So it may be roughly stated that the brain weights in the underfed young albino rats have values below the standard weights for the same age and above those for the same body weights, but always falling nearer to the standard age values.

6. THE SIZE AND SHAPE OF THE CEREBRUM

The five diameters of the cerebrum of the underfed young were measured and recorded according to the procedure already described in my first paper of this series (Sugita, '17, figs. 1 and 2). The measurement W.B, represents the greatest frontal diameter; the measurement W.D, the frontal diameter passing the middle point of the fissura sagittalis; the measurement L.G, the greatest distance from the frontal pole to the occipital

GROWTH OF THE CEREBRAL CORTEX

191

TABLE 4 Shuiv ng for each litter group in this study the average age, duration of isolation denoted by the percentage of the life span, observed body weight, compared with the standard body weight for the same age, and observed rain weight, compared with the standard values for the same age and the observed body weight, respectively. Standard values were all calculated by the use of the formulas given in 'The Rat' (Donaldson, '15). Within each litter the starved animals were divided nto two groups, T I having brains weighing less than 1.0 gram and T. II having brains weighing more than 1.0 gram. The control animals were also grouped in the same way into two groups, C. I and C. II. Averages ivere taken within each group. In lines designated 'percentage difference' (abbreviated 'per. diff.'), the deviations of the observed measuremmts from the standard values were given in percentage, the respective standard values being taken as standards of comparison. At the foot of the table, the average as to the test and control groups are given and the percentage differences from the standards are also ca'culated

TEST CONTROL

SEX

AVERAGE AGE

a a w

d fc

K «  Eh 1

BODY WEIGHT

BRAIN WEIGHT

SERIES, LITTER AND GROUP

Observed

Standard according to age

Ob served

Stanflard according to age

Standard according to observed body weight

days

per cent

gramf

(jrains

grams

grams

grams

Series I

A 0, a, d, f

T. I

1 m, 3 f

t —

32

7.2

.9.7

0.584

0.6U

0.441

h

T. II

1 f

15

44

13.9

16.5

1.C24

1.048

0.952

(per. diff.)

(-19)

(- 5)

(+15)

b, e, g

C. I

3 m

S

11.7

10.9

0.740

0.750

0.790

i

C. II

1 f

17

30.1

18.1

1.278

1.099

1.301

(per. diff.)

(+44)

(+ 9)

(- 4)

Series I

B a, c, e, f

T. I

3 m, 1 f

9

30

7.3

in

0.644

0.775

0.468

i

T. II

1 m

19

44

12.7

18.7

1.052

1 .131

0.901

(per. diff.)

(-34)

(-11)

(+24)

b, d

C. I

2 f

6

7.1

8.6

0.543

0.559

0.437

g. h, J

C. II

3 f

18

20.5

18.7

1.144

1.112

1.148

(per. diff.)

(+ 1)

(+ 1)

(+ 6)

Series I

C a, c, d

T. II

2 in, 1 f

20

44

15.1

20.4

1.105

1.146

0.946

(per. diff.)

(-26)

(- 4)

(+17)

b, e

C. II

2 f

22

27.6

22.6

1.307

1.165

1.234

(per. diff.)

(+22)

(+12)

+ 6)

192

NAOKI SUGITA

TABLE i— Continued

TEST CONTROL

SEX

AVERAGE AGE

5 H H 3 2; b Q 0. 1=

« 2 > a

K > 6, CO

BODT WEIGHT

BRAIN WEIGHT

SERIES, LITTER AND GROUP

Observed

Standard according to age

Observed

Standard according to age

Standard according to observed body weight

Series I D a, c, d

e (per. diff.)

b

f

(per. diff.)

T. I T. II

C. I C. II

Im, 2f

1 m

1 m 1 m

days

12 18

9 22

per cent

57 65

grams

6.9 13.0

11.2 24.0

grams

14.0

18.0

(-38)

11.8 21.1 (+ 7)

grams

0.778 1.089

0.870 1.220

grams 0.943

1.112 (- 9)

0.840 1.184

(+ 3)

grams . 0.437

0.921

(+37)

0.782 1.237 (+ 4)

Series I E a, b, c, d

(per. diff.)

e. f (per. diff.)

T. I T. II

C. II

3m, If 2f

Im, If

1220

17

46 44

9.7 16.2

21.6

14.3 20.7 (-26)

17.S (+25)

0.835 1.122

1.179

0.977 1.159

(- 8)

1.077 (+ 9)

0.664

1.042

(+15)

1.171 (+ 1)

Series II

Fa, b

c-1

(per. diff.)

T. I T. II

Im, If 4 m, 6 f

13 25+

9.2 18.1

14.9 25.6 (-33)

0.832 1.204

1.000 1.231 (- 9)

0.631 1.046

(+21)

Series III

Ga-g

h-j

(per. diff.)

T. I T. II

4 m, 3 f 2m, If

11+ 22

8.3 13.0

13.6 21.5 (-39)

0.844 1.154

0.914 1.181

(- 5)

0.561 0.871 (+39)

Series II

H a

b-g (per. diff.)

T. I T. II

1 f 2 m, 4 f

13 30

8.8 17.2

15.1 31.5

(-44)

0.880 1.156

1.003 1.298 (-12)

0.600 1.045 (+24)

Average 1

(Series I-III)J

(per. diff.)

Average }

(Series I-III)j

(per. diff.)

T. I T. II

11 21 +

8.2 14.9

13.3 (-38)

21.6 (-31)

0.771 1.113

0.895

(-14)

1 . 163

(- 4)

0.543 (+42)

0.966

(+15)

GROWTH OF THE CEREBRAL CORTEX

193

TABLE i— Continued

TEST CONTROL

SEX

AVERAGE AGE

. !Z H W O O fa

p. K

BODY WEIGHT

BRAIN WEIGHT

SERIES, LITTER AND GROUP

Observed

Standard according to age

Observed

Standar 1 according to age

Standard according to observed boily weight

Average 1

(Series I) J

(per. diff.)

C. I

days

8

per cent

grn7ns

10.0

grams

10.4

(- 4)

grams

0.718

grains 0.716

(+ 0)

grams

0.670

(+7)

Average \

(Series I) /

(per. diff.)

C. II

19+

24.8

19.6

(+27)

1.226

1.127 (+ 9)

1.218

(+ 1)

pole; the measurement L.F, the sagittal diameter from the frontal to the occipital pole running parallel to the sagittal fissure, and the measurement Hi. is the greatest vertical height at the stalk of the hypophysis. In table 5, which was condensed from table 5 a (unpubhshed) for each individual, the average brain weight, the average measurements W.B, L.G and Ht. are given for each group, both test and control, compared with the corresponding standard measurements for the brains of the same weight, which were originally calculated for each individual using the formulas formerly presented by me (Sugita, '17), and then condensed. The measurements L.F and W.D are given, also condensed for each group, in table 9.

On examining table 5, it appears that the measurement W.B of the underfed is smaller on the average by 2 per cent (average of all eight litters, T. groups only) than standard for the brains of the same weight, while the measurement L.G of the underfed is greater on the average by 2 per cent (average of all eight litters, T. groups only). The height in the underfed seems to be slightly less, by about 1 per cent on the average. On the other hand, if the controls be considered in the same way, they show also slight deviations from the calculated standard values, thus, on the average (Litters A to E, C. groups only), W.B is smaller by 1 per cent, L.G greater by 0.8 per cent and Ht. smaller by about 3 per

THE JOURNAL OF COMP.^R.^TIVE NEUROLOGY, VOL. 29. NO. 3

194 NAOKI SUGITA

cent in the controls. As a matter of fact, the measurement of Ht. could not be so accurate on' account of difficulty in fixing the dorsal limit, so that these slight differences in Ht. should not be taken too seriously. The measurement of L.G and W.G can be made accurately so that these results are trustworthy.

Taking these deviations in the controls into account, the general statement may be made that underfeeding alters the shape of the cerebrum, so that it becomes slightly elongated, when compared with the normal cerebrum of the same weight. This difference is probably due to the fact that, although the underfed cerebrum is arrested in growth, it nevertheless tends to enlarge normally and, as already determined (Sugita, '17) becomes more and more elongated as the age advances.

If, for the brains of like weight, the width-length indices

obtained bv the formula ^^^ are compared between

L.t

the underfed and the controls (compare table 9) or the standard values (based on table 3, Sugita, '17), it will be seen that the index value tends to be lower in the underfed, especially in the members of Litters F and G which were underfed continuously and rather severely. In the latter litters the index values for each individual are smaller by 2 to 7 points than the index values for the standard brains of like weights (the data for these calculations are contained in table 9 a, not here published). The average index values in Litters F and G are 102 (for T. I groups) and 97 (for T. II groups), while the corresponding standard values are, respectively, 106 and 103 (Sugita, '17).

7. THICKNESS OF THE CEREBRAL CORTEX

Tables 6 a, 6 b, and 6 c (all unpublished) were originally prepared to give the cortical thickness for each individual as measured at the localities I to VIII in the sagittal and frontal sections and to give the average cortical thickness in each section and the general average thickness, to be compared with the respective standards presented in a former paper (Sugita, '17a). Table 6, which follows, contains in condensed form the corrected data for the thickness of the cerebral cortex of the underfed Albinos and that of

TABLE 5

Giving for each litter group in this study the average brain weight and the average tneasurements L.G, W.B and Hi. of the cerebrum, each corn-pared with the corresponding standard values for the same brain weight, calculated by the use of the for7nulas given by. me (Sugita, '17). The averages for the test and control groups are given at the foot of the table.

SERIES, LITTER AND

TEST CONTROL

AVERAGE BRAIN WEIGHT

W.

B.

L.

G.

Ht.

Observed

Standard

Observed

Standard

Observed

Standard

grams

turn.

mm.

mm.

Tnm.

mm.

mm.

Series I

A c, a, d, f

T.

0.584

10.79

10.94

9.69

9.20

6.99

7.06

h

T.

1.024

13.05

13.00

12.30

12.30

8.45

8.70

b, e, g

C.

0.740

11.63

11.90

10.73

10.63

7.50

7.68

i

C.

1.278

13.85

14-00

13.15

13.25

8.95

9.30

Series I

B a, c, e, f

T.

0.644

11.11

11.38

10.25

9.96

7.36

7.38

i

T.

1.052

13.20

13.15

12.35

12.40

8.50

8.75

b, d

C.

0.543

10.50

10.78

9.73

9.18

6.90

6.95

g., h, j

C.

1.144

13.47

13.48

12.75

12.77

8.68

9.00

Series I

C a, c, d

T.

1.105

13.10

13.35

12.72

12.62

8.70

8.88

b, e

C.

1.307

13.78

14-10

13.63

13.33

8.83

9.40

Series I

D a, c, d

T.

0.778

11.67

12.17

11.25

10.80

7.98

7.92

e

T.

1.089

12.90

13.30

12.75

12.55

8.60

8.85

b

C.

0.870

12.25

12.60

11.40

11.65

8.00

8.20

f

C.

1.220

13.95

13.80

13.30

13.05

8.80

9.20

Series I

E a, b, c, d

T.

0.835

12.08

12.41

11.35

11.16

8.29

8.10

g, h

T.

1.122

13.35

13.40

12.68

12.70

8.98

8.95

e, f

C.

1.179

13.55

13.60

12.78

12.85

8.88

9.05

Series II

F a, b

T.

0.832

12.00

12.53

11.50

11.13

7.95

8.05

c-1

T.

1.204

13.30

13.73

13.11

12.98

9.30

9.15

Series III

Ga-g •

T.

0.844

12.22

12.46

11.46

11.32

8.13

8.69

h-j

T.

1.154

13.27

13.53

13.03

12.80

8.95

9.00

Average 1

T.

0.753

11.65

11.98

10.92

10.60

7.78

7.87

(Ser. I-III)J

T.

1.107

13.17

13.35

12.71

12.62

8.78

8.90

Average 1

C.

0.718

11.46

11.76

10.62

10.49

7.47

7.61

(Ser. I) /

C.

II.

1.226

13.72

13.80

13.12

13.05

8.83

9.19

195

196 NAOKI SUGITA

the controls from the same litter, and it gives for each group, underfed and controls, the average brain weight and the corrected cortical thickness in the sagittal and frontal sections of the brain, together with the average thickness. The data for obtaining the correction-coefficient are given in the full table for each individual, but in the condensed table 6 orily the average values of the correction-coefficients for each group appear. The application of the correction-coefficient was made in the way formerly described (Sugita, '17 a). The horizontal sections of underfed brains were not prepared for this study.

Table 6 shows also a comparison of the average thickness of the cortex in the underfed young with that for the standard Albino of the same brain weights. As the present study was not extended to the horizontal sections, the average thickness of the cortex was determined from only the two kinds of sections from the same individual and it was compared with the corresponding average for the standards. In the standards, these values proved to be within 0.5 per cent of the general average thickness of the cortex based on the three kinds of sections. Here, in table 6, the standard values were obtained from the somewhat smoothed curve based on the data formerly presented (table 9 and chart 9, Sugita, '17a).

Table 6 a (unpubhshed) for the sagittal section showed for the underfed that the cortical thickness at the frontal pole (locality I) is evidently very much greater than that of the controls or the corresponding standard value for the same brain weight, comparison having been made on the basis of the data given formerly (table 6 and chart 4, Sugita, '17 a). Locality II was the next which exceeds in the cortical thickness on the side of the underfed. Localities III and IV stand in general slightly in favor of the underfed, but at locality V, the occipital pole, there was found no notable difference in the cortical thickness between the underfed and the standard. As a rule, the cortical thickness of the normal Albino diminishes from the frontal to the occipital pole — from locality I to locality V — and the cortex at the frontal pole increases most rapidly in the early age. This is also just the order of the excesses in the cortical thickness of the underfed

GROWTH OF THE CEREBRAL CORTEX 197

when compared with the standard values for the brains weighing the same. The cortical thickness at each locality of the controls was on the average fairly in accord with the standard (the detailed evidence for these conclusions is contained in table 6 a, not here published).

In table 6 b (unpublished), in which the cortical thickness at localities VI, VII, and VIII of the frontal section was given, it was also clearly seen that the localities VI and VII are much greater in the cortical thickness, compared with those of the controls or the standard values of the same brain weight. The excess amounts on the average to more than 10 per cent. The locality VIII, at which the cortex is heterogeneous in laminar structure, did not show any significant difference in the cortical thickness, compared with the normal, though in some cases here and there it was found somewhat thicker in the underfed (the evidence for these determinations is contained in table G b, not here published).

One more notable thing found in the cerebral cortex of the underfed was that, while in the controls and standards the locality VII is always somewhat greater in thickness than the locality VI, the relation has, in many cases (18 out of 44) of the underfed, proved to be reversed (A a, h; B i; C a, c; D d, e; E c, h; F b, c, f, h; G a, c, g, e and h).

Generally considered, the localities which are situated nearer to the ventricular wall, the locus of the cell division, seem to have gained much more in the cortical thickness in the case of the underfed, while the localities remote from the matrix (for example, locality V) or the part constructed heterogeneousl}^ (for example, locality VIII) appear to be modified but little by underfeeding.

As is to be seen in table 6, the average thickness of the cortex is in favor of the underfed Albinos. If compared with the standard values for the same brain weight, the average cortical thickness in the underfed young (table 6) is greater than tjie standard on the average by 7 per cent (average of all eight litters, T. groups only), while t^e controls are greater on the average by only 1.8 per cent (average of Litters A to E^ C. groups only). According

198

NAOKI SUGITA

TABLE 6 Giving for each litter group in this study the average age, brain weight, and the average cortical thickness in the sagittal and frontal sections. The general average cortical thickness was obtained and compared with the standard value for the same brain weight, quoted from a previous paper (Sugita, '17a). The data for each individual and for each locality of the cortex were originally tabulated in three full tables (tables 6a, 6b and 6c) which are on file at The Wistar Institute and from which this table 6 was condensed. The correction-coefficients are given in averages for each litter group for each kind of section. The averages for the test and control groups are given at the end of the table.

TEST CONTROL

AVERAGE AGE

AVERAGE BRAIN WEIGHT

SAGITTAL SECTION

FRONTAL SECTION

AVERAGE

SERIES, LITTER AND GRODP

Correction coefficient

Cortical thickness

Correction

coefficient

Cortical

thickness

Cortical

thickness

Standard for the same brain weight

days

grams

mm.

mm.

mm.

mm.

Series I

A c, a, d, f

T.

7

0.584

1.16

1.24

1.18

1.47

1.35

1.'9

h

T.

15

1.024

1.21

1.64

1.28

2.05

1.85

1.73

> b, g

C.

8

0.688

1.09

1.34

1.14

1.46

1.40

1.38

i

C.

17

1.278

1.23

1.77

1.26

2.00

1.89

1.84

Series I

B a, c, e, f

T.

9

0.644

1.12

l..;3

1.17

1.53

1.43

1.40

i

T.

19

1.052

1.20

1.66

1.37

2.15

1.91

1.74

b, d

C.

6

0.543

1.08

1.18

1.09

1.32

1.25

1.25

g, h, j

C.

18

1.144

1.24

1.74

1.31

2.01

1.88

1.80

Series I

C a, c, d

T.

20

1.105

1.17

1.74

1.25

2.08

1.91

1.77

b, e

C.

22

1.307

1.17

1.76

1.16

1.97

1.87

1.85

Series I

D a, c, d

T.

12

0.778

1.15

1.54

1.24

1.89

1.72

1.61

e

T.

18

1.089

1.17

1.73

1.28

2.10

1.92

1.77

b

C.

9

0.870

1.13

1.55

1.22

1.87

1.71

1.67

f

C.

22

1.220

1.14

1.78

—

—

1.82

Series I

E b, c, d ,

T.

12

0.867

1.11

1.53

1.23

1.95

1.74

1.66

g, h

T.

20

1.122

1.20

1.81

1.26

2.15

1.98

1.79

e, f

C.

II

17

1.179

1.10

1.68

1.21

1*94

1.81

1.79

GROWTH OF THE CEREBRAL CORTEX

199

TABLE 6

-Continued

TEST CONTROL

AVERAGE AGE

AVERAGE BRAIN WEIGHT

SAGITTAL SECTION

FRONTAL SECTION

AVERAGE

SERIES, LITTER AND GROUP

Correction coefficient

Cortical thickness

Correction coefficient

Cortical

thickness

Cortical thickness

Standard for the same brain weight

days

grams

mm.

mm.

mm.

mm.

Series II

Fa, b

T. I

13

0.832

1.17

1.57

1.21

1.8

1.72

1.62

c-1

T. II

25+

1.204

1.24

1.81

1.32

2.15

1.98

1.82

Series III

Ga-g

T. I

11 +

0.844

1.14

1.55

1.24

1.89

1.72

1.63

h-j

T. II

22

1.154

1.19

1.78

1.26

2.15

1.97

1.80

Average 1

T. I

11

0.758

1.14

1.46

1.21

1.77

1.61

1.54

(Her. I-III) j

T. II

20

1.107

1.20

1.74

1.29

2. 2

1.93

1.77

Average 1

C. I

8

0.700

1.10

1.36

1.15

.55

1.45

US

(Ser. I) /

C. II

19+

1.226

1.18

1.75

1. 4

1.98

1.86

1.82

to table 6 c (unpublished), which gives comparisons of cortical thickness of the underfed with the standard in each section, the average cortical thickness in the sagittal section of the underfed exceeds the standard on the average by 5.3 per cent and that in the frontal section of the underfed on the average by 8.7 per cent.

8. AREA OF THE CORTEX IN THE SAGITTAL AND FRONTAL SECTIONS

Following the procedures which have been described earlier for the measurement of the area of the cortex in the sagittal and frontal sections of the Albino brains (Sugita, '18 b), the data for the underfed Albinos were obtained. Table 7 presents in condensed form for each group the averaged data on the corrected area of the cortex together with the average correction-coefficient for each group, in the sagittal and frontal sections, respectively. The observed data, as measured on the slides, and the data for correction-coefficient for each individual were tabulated in tables 7 a and 7 b (unpublished), on the basis of which table 7 was made. In table 7 (and in table 7 b) the total areas of the frontal sections (one hemicerebrum) and the percentage of the cortical area to the total area of the section are also entered.

200

NAOKI SUGITA

TABLE 7

Giving for each litter group in this study the average brain weight, the corrected areas of the cortex in the sagittal and frontal sect'ons, and the total area of the frontal section and the average correction-coefficients for each group for each kind of section. The percentage values of the cortical area to the area of the total section in the frontal section are also given for each group. This table was condensed from two detailed tables for individual observed data and the data for the correction-coefficients. The averages for the test and control groups are given at the foot of the table

TEST CONTROL

AVERAGE

BRAIN WEIGHT

SAGITTAL SECTION

FRONTAL

SECTION

SERIES, LITTER AND GROUP

Correction-coefficient

Area of cortex

Correction-coefficient

Area of cortex

Total area of section

Percentage of cortical area to the total

area

grams

mm."

mm,.

mm.

per cent

Series I

A c, a, d, f

T. I

0.584

1.16

14.6

1.18

13.4

28.8

45

h

T. II

1.024

1.21

22.2

1.28

22.8

45.0

51

b, g

C. I

0.688

1.09

17.4

1.14

15.2

31.9

46

i

C. II

1.278

1.23

27.4

1.26

21.7

43.6

50

Series I

B a, c, e, f

T. I

0.644

1.12

16.9

1.17

15.0

31.6

47

i

T. II

1.052

1.20

23.3

1.37

23.4

45.7

51

b, d

C. I

0.543

1.08

9.1

1.09

11,6

25.1

46

g, h, j

C. II

1.144

1.24

24.6

1.31

21.7

45.3

47

Series I

C a, c, d

T. II

1 . 105

1.17

24.5

1.25

22.0

43.6

50

1), e

C. II

1.307

1.17

27.8

1.16

22.2

46.0

48

Series I

D a, c, d

T. I

0.778

1.15

19.4

1.24

17.9

36.1

50

e

T. II

1.089

1.17

24.2

1.28

20.0

41.0

49

b

C. I

0.870

1.13

20.6

1.11

18.7

38.8

48

f

C. II

1.220

1.14

26.7

—

—

—

—

Series I

•

E b, c, d

T. I

0.867

1.11

19.9

1.23

19.8

38.4

52

g. h

T. II

1.122

1.20

25.9

1.26

23.4

45.9

51

e, f

C. II

1.179

1.10

24.2

1.21

22.2

45.2

49

Series II

F a, b

T. I

0.832

1.17

20.8

1.21

18.6

38.0

50

c-I

T. II

1.204

1.24

26.0

1.32

23.4

47.3

50

GROWTH OF THE CEREBRAL CORTEX

201

TABLE l^Continued

TEST CONTROL

AVERAGE

BRAIN WEIGHT

SAGITTAL

SECTION

FRONTAL

SECTION

SERIES, LITTER AND GROUP

Qorrection-coefficient

Area of cortex

Correction-coefficient

Area of cortex

Total area of section

Percentage of

cortical

area to

the total

area

grams

mm 2

mm.

mm .

per cent

Series III

G a-ig

T.

I

0.844

1.14

20.1

1.24

19.2

38.5

50

h-j

T.

II

1.154

1.19

25.6

1.26

22.9

46.2

50

Average 1

T.

I

0.758

1.14

18.6

1.21

17.3

35.2

49

(Ser. I-III)j

T.

II

1.107

1.20

24.5

1.29

22.6

45.0

50

Average \

C.

I

0.700

1.10

15.7

1.15

15.2

31.9

48

(Ser. I) /

C.

II

1.226

1.18

26.1

1.24

22.0

45.0

49

The above-mentioned corrected data for each individual were separately paired with the corresponding standard values for the same brain weight, quoted from my previous study (Sugita, '18 b) in table 8 a (unpul)lished) and from this latter table 8 was condensed, giving only the averages for each group.

Briefly stated, the area of the cortex in the sagittal section of the underfed is on the average greater by 1.4 per cent (average of all eight litters, T. groups only) than in the standard, while the controls are on the average about 1.9 per cent less than the standard.

The average area of the total frontal section is in the underfed greater than that of the standard by 2.4 per cent (average of all eight litters, T. groups only), while the controls are less by 3.8 per cent (average of Litters A to E, C. groups only) than the standard, and the area of the cortex in the frontal section is in the . underfed greater on the average by 5.0 per cent, while in the controls less by 2.1 per cent, than the standard (table 8). From these observations, it may be easily concluded that in the underfed the proportion of the cortex to the total section is higher than in the standard or control, as shown by the percentage values directly calculated for each brain (table 7 b) and given in a condensed form in the last column of table 7, where the values are

202

NAOKI SUGITA

TABLE 8

Giving for each litter group in this study the average brain iveight, the corrected areas of the cortex in the sagittal and frontal sections, and the area, of the entire frontal section, respectively, compared tvith the corresponding standard values for the same brain weight. The standard values are all entered according to my previous presentation (Sugita, '18b). This table was condensed from an original complete table 8a for each individual. The averages for the test and control groups are given at the end of the table.

AVER

SAGITTAL SECTION

FRONTAL SECTION

Area of cortex

Tota

area

Area of cortex

SERIES, LITTER AND

AGE

BRAIN

WEIGHT

GROUP

Corrected

Stan^^ard

Area

Corrected

Standard

Corrected

Standard

Area

Thick

Thick

ness

ness

grams

mm.

mm.

mm.

mm. 2

mm.

wm.2

mm.'

mm.

Series I

A c, a, d, f

0.584

14.6

13.8

11.4

28.8

28.3

13.4

12.9

8.9

h

1.024

22.2

23.0

13.5

45.0

42.0

22.8

20.7

11.1

b, g

0.688

17.4

16.0

12.6

31.9

31.8

. 15.2

15.0

10.1

i

1.278

27.4

26.7

15.5

43.6

48.5

21.7

23.0

10.9

Series I

B a, c, e, f

0.644

16.9

15. Jt

12.5

31.6

30.4

15.0

14.2

9.6

i

1.052

23.3

23.6

14.0

45.7

43.0

23.4

21.0

10.9

b, d

0.543

13.1

13.0

11.0

25.1

28.3

11.6

11.9

8.6

g, h, j

1.144

24.6

25.2

14.1

45.3

45.2

21.7

21.7

10.8

Series I

C a, c, d

1.105

24.5

2Jt.h

14.0

43.6

44.1

22.0

21.5

10.6

b, e

1.307

27.8

27.1

15.8

46.0

49.3

22.2

23.3

11.3

Series I

D a, c, d

0.778

19.4

18.9

12.6

36.1

34-8

17.9

17.0

9.5

e

1.089

24.2

24.5

14.0

41.0

44-0

20.0

21.3

9.5

b

0.870

20.6

20.5

13.3

38.8

38.0

18.7

18.8

10.0

f

1.220

26.7

26.0

15.0

—

47.0

—

22.5

—

Series I

E b, c, d

0.867

19.9

20.3

13.0

38.4

37.5

19.8

18.7

10.1

g, h

1.122

25.9

25.0

14.3

45.9

44.5

23.4

21.5

10.9

e, f

1.179

24.2

25.3

14.4

45.2

46.0

22.2

23.6

11.4

GROWTH OF THE CEREBRAL CORTEX 203

TABLE 8— Continued

AVER

SAGITTAL SECTION

FRONTAL SECTION

Area of cortex

Tota

area

Area of cortex

SERIES, LITTER AND

AGE

BRAIN

WEIGHT

GROUP

Corrected

Sttt7ld ard

Area

Corrected

Standard

Corrected

Standard

Area

Thick

Thick

ness

ness

grams

mm. 2

nim.

mm.

m,m.'

mm."

mm. 2

m.m.

TOTO.

Series II

F a, b

0.832

20.8

19.4

13.2

38.0

36.5

18.6

17.9

9.9

c-1

1.204

26.0

25.9

14.4

47.3

46.7

23.4

22.3

10.9

Series III

Ga-g

0.844

20.1

19.8

13.0

38.5

36.9

19.2

18.2

10.2

h-j

1.154

25.6

25.7

14.3

46.2

45.3

22.9

21.9

10.7

Average 1 (T. I)

0.758

18.6

17.9

12.6

35.2

34-1

17.3

16.5

9.7

(Ser. I-III)/ (T.II)

1.107

24.5

24.6

14.1

45.0

44-2

22.6

21.5

10.7

Average\ (C. I)

0.700

15.7

16.5

12.3

31.9

32.7

15.2

15.2

9.6

(Ser. I) / (C. II)

1.226

26.1

26.1

15.0

45.0

47.2

22.0

22.8

11.1

higher on the average by 3 per cent (1 to 4 per cent in individual cases) than the standard or controls. These results fit with the observation that in the underfed the cortical thickness in the frontal section is 8.7 per cent greater than for the standard (chapter 7).

9. COMPUTED VOLUME OF THE CORTEX

In a former paper (Sugita, '18 b), it was assumed that, as the form of the cerebrum of the albino rat is relatively simple and nearly constant, the relative volumes occupied by the cortical cells could be computed, and compared among themselves, by reducing the data obtained by measurement to a simple geometrical form, since the cortical areas in the sagittal and frontal sections stand in fixed relations to the respective diameters L.F and W.D and to the cortical thickness of the sections from the same brain. These relations have been expressed as follows (Sugita, '18 b):

204 NAOKI SUGITA

Cortical area (mm.-) in sagittal section

L.F (mm.) ^ constant (1)

Cortical thickness (mm.) in the same

Cortical area (mm.-) in frontal section ^rr t^ / x , , .^s

-7s — T- — 1 xi- r } w — Til -=- **^ Mimm..) = constant (2)

Cortical thickness (mm.) m the same ^ ^

And the computed volume of the cortex should be obtained simply by the following formula :

L.F X W.D X T (ah in millimeters), (3)

where T gives the general average thickness of the cerebral cortex of the same brain.

As shown in table 9, which has been condensed from table 9 a (unpublished) for each individual, the constant ratios obtained by the above formulas (1) and (2) fall between 1.10 and 1.29 for the sagittal sections and between 0.80 and 0.95 for the frontal sections, throughout both the underfed and the control groups. The averages of the ratios for the sagittal and frontal sections of the underfed are, respectively, 1.18 and 0.88, and those of the controls are, respectively, 1.20 and 0.88. I have previously given the figures 1.22 and 0.91, respectively, as these ratios of the standard albino rat brains weighing more than 0.5 gram. So it may be assumed that the ratios are nearly the same in both the underfed and the controls; slight differences in the underfed from the standard may be regarded as due to the facts that the cerebrum of the underfed is slightly more elongated and the cortical thickness is somewhat greater than in the standard. As the product of the coefficients in the underfed (I'.IS X 0.88) falls somewhat lower than that in the standard (1.22 X 0.91), the results of L.F X W.D X T should be about 5 per cent higher in the underfed than in the standard.

The relative volumes of the cortex, obtained by the formula (3), are computed and given in table 11 (without any special correction), compared with the corresponding standard values for brains of the same age, instead of for brains of the same weight. The relative volume of the cortex in the underfed brains, which are considerably retarded in total weight development, is greater than for the standard brains of the .same weight, which are necessarily younger and less developed as regards the cortical elements than the underfed brains of like weight.

GROWTH OF THE CEREBRAL CORTEX 205

Since in the underfed the average cortical thickness in the sagittal and frontal sections was used in place of the standard T, based on the thickness of the sagittal, frontal and horizontal sections (compare Sugita, '17 a), therefore corresponding values of T have been used in calculating the standard values for the present comparison.

For this comparison, the test animals may be considered in two groups, T. I and T. II. In T. I groups, in which all test rats have a brain weight less than 1.0 gram, the average computed volume of the cortex is less than the standard by 16 per cent, while in T. II groups, which contain the test rats with brains weighing above 1.0 gram, it is more than the standard on the averagfe by 1 per cent. On the other hand, the cortical volume in C. I groups, which embraces the controls having brain weights less than 1.0 gram, is on the average 2.4 per cent less, and in C. II groups, the controls with brain weights above 1.0 gram, it is on the average 7.5 per cent more than the standard for the same age (table 11, last lines). As these comparisons are based on the numbers obtained by calculation and not on the direct measurement, slight discrepancies cannot be regarded as significant, and, as already noted, the results in the underfed are open to special correction of a few per cent for an accurate comparison.

The underfed brains are much retarded in the weight development and the brains weighing up to 1.0 gram include those of ages up to sixteen days, at which age the normal rats have a brain weight 10 per cent heavier than the test rats (chapter V). We conclude, therefore, that, calculated by the formula L.F X W.D X T, the relative volumes of the cortex in the underfed are nearly the same as in the standard in the brains weighing more than 1.0 gram (T. II groups), while, on the contrary, they are considerably smaller than the standard in the case of the brains weighing under 1.0 gram or under the age of sixteen days, if the age be taken as the standard of comparison.

It appears, therefore, that in rats underfed severely the cortical volume is considerably retarded in growth during the early period of development, but this is probably fairly compensated later when the brain attains a weight of more than 1 .0 gram or an age

206

NAOKI SUGITA

TABLE 9

Giving for each litter group in this study the average brain weight, the measurements L.F and W.D, the quotient of the cortical area divided by the cortical thickness {given also in table 8), and the ratio of the latter to the measurement L.F or W .D, for the sagittal and frontal sections. The width-length index which is obtained by {W .D X 100)/L.F is also given. This table was condensed from an U7ipublished table 9a for each individual. The averages for the test and control groups are given at the foot of the table. The ratios given in this table 9 are based on the average of the individual ratios a7id not on those obtained directly from the average L.F or W.D and the average quotients

H

CORT.

CORT.

TEST CONTROL

<

m a <

AVERAGE BRAIN WEIGHT

L.F

.\REA

RATIO

W. D

AREA

RATIO

z

SERIES, LITTER AND GROrP

CORT.

THICKN.

IN

SAGITTAL

CORT. THICKN.

IN FRONTAL

is

•<:

SECTION

SECTION

^

days

grams

mm.

7nm.

mm.

mm.

Series I

A c, a, d, f

T.

7 —

0.584

9.28

11.4

1.23

9.88

8.9

0.89

106

h

T.

II

15

1.024

11.85

13.5

1.14

12.00

11.1

0.93

101

b, g

c.

8

0.688

9.90

12.6

1.27

10.60

10.1

0.95

107

i

c.

II

17

1.278

12.95

15.5

1.20

12.85

10.9

0.84

-99

Sey-ies I

B a, c, e, f

T.

9

0.644

9.70

12.5

1.29

10.46

9.6

0.92

108

i

T.

II

19

1.052

12.10

14.0

1.16

12.45

10.9

0.88

103

b, d

C.

6

0.543

8.78

, 11.0

1.24

9.85

8.0

0.88

112

g, h, J

C.

II

18

1.144

12.28

14.1

1.16

12.40

10.8

0.87

101

Series I

C a, c, d

T.

II

20

1.105

12.32

14.0

1.14

12.17

10.6

0.87

99

h, e

C.

II

22

1.307

13.30

15.8

1.19

12.98

11.3

0.87

98

Series I

D a, c, d

T.

12

0.778

10.90

12.6

1.15

10.77

9.5

0.88

99

e

T.

II

18

1.089

12.25

14.0

1.14

11.85

9.5

0.80

97

b

C.

9

0.870

10.95

13.3

1.21

11.45

10.0

0.82

104

f _

C.

II

22

1.220

12.40

15.0

1.21

12.80

—

—

103

Series I

E b, c, d

T.

12

0.867

10.65

13.0

1.22

11.30

10.1

0.90

106

g, h

T.

II

20

.1.122

12.10

14.3

1.19

12.35

10.9

0.88

102

e, f

C.

II

17

1.179

12.23

14.4

1.18

12.48

11.4

0.92

102

GROWTH OF THE CEREBRAL CORTEX

207

TABLE Q— Continued

»

CORT.

CORT.

SERIES, LITTER AND GROUP

TEST CONTROL

o

<;

H

<

AVERAGE BRAIN WEIGHT

L.F

AREA

CORT.

THICKN.

IN SAGITT.\L

RATIO

W. D

AREA COKT.

THICKN. IN

FRONTAL

RATIO

m 1 X

Q 2

>

<

SECTION

SECTION

?

days

grams

mm.

mm.

mm.

mm..

Series II

F a, b

T.

I

13

0.832

11.18

13.2

1.19

11.23

9.9

0.88

101

c-1

T.

II

25+

1.204

12.66

14.4

1.14

12.30

10.9

0.88

97

Series III

Ba-g

T.

I

11 +

0.844

10.99

13.0

1.18

11.22

10.2

0.90

102

h-j

T.

II

22

1.154

12.58

14.3

1.14

12.20

10.7

0.87

97

Average 1

T.

I

11

0.758

10.45

12.6

1.21

10.81

9.7

0.90

104

(Ser. I-III)/

T.

II

20

1.107

12.27

14.1

1.15

12.19

10.7

0.87

99

Average \

C.

I

8

0.700

9.88

12.3

1.24

10.63

9.6

0.88

108

(Ser. I) /

C.

II

19+

1.226

12.63

15.0

1.19

12.70

11.1

0.88

101

of more than sixteen days, so that after this period there is no longer any significant difference in the cortical volumes between the test and the standard animals.

10. NUxMBER OF NERVE CELLS IN THE CEREBRAL CORTEX •

The actual number of nerve cells in the frontal cortex in a unit volume of 0.001 mm,^, or 0.1 mm.^ in area on the shde by 10 micra in thickness, was counted in the lamina pyramidalis and in the lamina ganglionaris at locality VII, the middle part of the cortical band of the frontal section. The procedure for counting the cell number, adopted by me for the standard values and described in my previous paper (Sugita, '18 b), has been strictly followed here also. The number of cells in the lamina pyramidalis and the lamina ganglionaris and the number of the ganglion cells in a unit volume have been recorded and then converted into the number of cells in the same unit volume in the fresh condition of the brain by the use of the correction-coefficients based on observations. All the data have been tabulated in table 10 a (unpublished) and condensed in table 10 for each group. The

208

NAOKI SUGITA

TABLE 10

Givitig for each litter group in. this study the average age, hraiti, weight, correctioncoefficient, and the corrected number of nerve cells in a unit volume {0.001 mm.^) in the lamina pyramidalis and the lamina ganglionaris and the corrected number of ganglion cells only in the same volume, measured at locality VII. This table was condensed from a detailed table, table 10a (unpublished), which gives the same data for the individual cases. The averages for the test and qpntrol groups are given at the foot of the table.

TEST

AVERAGE

AVERAGE

CORRECTION

NUMBER OF CELLS IN

0.001 mm.'

GROUP

CONTROL

AGE

WEIGHT

COEFFI

Lamina

Lamina

Ganglion

CIENT

pvrami

gansjlio

cells in

dalis

nans

lam. gangl.

days

grams

Series I

•

A c, a, d, f

T. I

7 —

0.584

1.18

271

167

47

h

T. II

15

1.024

1.28

120

86

21

b, g

C. I

8

0.688

1.14

224

131

40

i

C. II

17

1.278

1.26

107

75

20

Series I

B a, c, e, f

T. I

-9

0.644

1.17

232

132

39

i

T. II

19

1.052

1.37

117

77

19

b, d

C. I

6

0.543

1.09

268

177

58

g, h, i

C. II

18

1.144

1.31

109

76

21

Series I

C a, c, d

T. II

20

1.105

1.25

109

73

20

b, e

C. II

22

1.307

1.16

109

79

26

Series

D a, c, d

T. I .

12

0.778

1.24

152

90

21

e

T. II

18

1.089

1.28

118

81

18

b

C. I

9

0.870

1.22

152

93

27

f

C. II

22

1.220

1.14

111

75

22

Series I

E a, b, c, d

T. I

12

0.835

1.21

144

101

25

g, h

T. II

20

1.122

1.26

116

79

21

e, f

C. II

17

1.179

1.21

116

79

23

Series II

Fa, b

T. I

13

0.832

1.21

162

98

29

c-1

T. II

25+

1.204

1.32

105

74

19

GROWTH OF THE CEREBRAL CORTEX

209

TABLE 10— Continued

TEST CONTROL

AVERAGE AGE

AVERAGE

BRAIN WEIGHT

CORRECTION COEFFICIENT

ND.MBER OP CELLS IN 0.001 mm.^

GROUP

Lamina

pyrami dalis

Lamina

ganglio naris

Ganglion

cells in

lam.gangl

Series III Ga-g

days

T. I T. II

grams 11 +

22

0.844

1.154

1.24 1.26

149 108

94 80

24 20

Average ) (Ser. I-III)/

Average ) (Ser. I) /

T. I T. II

C. I C. II

1120 819+

0.753 1.107

0.700 1.226

1.21 1.29

1.15 1.24

185 113

215 110

, 114

79

134

77

31 20

42 22

sum of the cell numbers in the lamina pyramidalis and the lamina ganglionaris, which may be regarded as representing the average cell density in the cerebral cortex, are also given in table 11, as A^, and compared with the corresponding standard values for the brains of the same age, taken from a former paper (Sugita, '18 b). When compared in this way, it is seen that the observed cell number in a unit volume is generally higher than the standard in brains which weigh less than 1.0 gram (T. I groups). The excess in cell number in underfed brains weighing less than 1.0 gram (T. I groups) is on the average 17 per cent, and that of the control brains weighing less than I.O gram (C. I groups) is on the average about 7 per cent. On the other hand, the average cell number of the underfed brains weighing more than 1.0 gram (T. II groups) is almost equal to, while that of the control brains weighing more than 1.0 gram (C. II groups) is less by 4 per cent than, the standard for the same age. The underfed brains are underdeveloped in weight and the brains weighing less than 1.0 gram (T. I groups) contain those of ages up to sixteen days. These relations lead me to conclude that, in the underfed brains weighing less than 1.0 gram or under sixteen days in age, the cell density denoted by A^ (the average cell number in two unit volumes) is distinctly high, when compared with the normal brains of the same age, probably because the brain size or weight

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 3

210 NAOKI SUGITA

or the cortical volume is relatively undeveloped in comparison with the cell number (see above) . In older brains weighing more than 1.0 gram or of ages above sixteen days, these discrepancies have been somewhat balanced, but, when compared with the controls, the underfed brains remain generally slightly higher in the cell density even in rats of sixteen days or older.

Considered in relation to the facts presented in the previous chapter showing that the computed volume of the cortex is below the standard in the underfed brains weighing less than 1.0 gram, it may inferred that the underfed brains, underdeveloped in weight and size, have a relatively higher cell density, because the normal number of cells is crowded into a cortex of smaller total volume.

11. RELATIVE VALUE OF THE COMPUTED NUMBER OF CELLS IN THE ENTIRE CORTEX

As previously shown (Sugita, '18 b), the computed number of nerve cells in the entire cortex may be obtained and the values compared among themselves by the use of the following formula :

N X L.F X W.D X T {L.F, W.D and T, in millimeters),

where N means the relative cell density represented by the sum of the cell numbers in the unit volume in the lamina pyramidalis and in the lamina ganglionaris (that is, the number in two unit volumes), given in table 11, based on table 9, and L.F X W.D X T is the computed volume of the cortex, as already given in the foregoing chapter.

In table 11, these relative values for the volume of the cortex and for the cell number in the cortex in the underfed Albinos are given for each group, each paired with the corresponding standard values for brains of the same age, all condensed from table 11a (unpublished), which gives the corresponding data for each individual. Every standard value was taken from my previous presentation (Sugita, '18 b). Throughout the underfed and the controls, these pairs of figures seem to be nearly in accord, showing on the average only 1.7 per cent excess in the underfed and 3,4 per cent excess in the control brains (average

GROWTH OF THE CEREBRAL CORTEX 211

of all groups), as compared with the standards. As alreadynoted in chapter 9, the results obtained by the use of formulas are open to some error, and in addition the results in the underfed are subject to special correction of a few per cent for a fair comparison, so that the differences recorded may be regarded as probably insignificant and the computed cell number in the entire cortex of the underfed may presumably be considered as equal to the standard number for brains of the same age. If this is so, the process of the cell division in the cerebrum during early life must have been going on undistui"bed even by the severe underfeeding, though both the size and the weight of the brain have been arrested in development by this, in some cases very considerably.

12. SIZE OF NERVE CELLS

The standard size of the pyramids (in the lamina pyramidalis) and the ganglion cells (in the lamina ganglionaris) in the cerebral cortex of the albino rats at different ages was presented in my sixth paper (Sugita, '18 c). In the present study on the influence of the severe underfeeding upon the growth of the cerebral cortex, the size of the nerve cells in the cortex was also determined bj^ the measurement of the transverse and longitudinal diameters of the cell body and the nucleus in the pyramids (in the lamina pyramidalis) and in the ganglion cells (in the lamina ganglionaris) at locality VII in the frontal section, in the same manner as for the standard determinations (Sugita, '18 c). The results have been tabulated in table 12 a (unpublished) and condensed in table 12 for each group. The average diameters of the cell body and of the nucleus are obtained by extracting the square roots of the respective products of the transverse by the longitudinal diameters, and these have been corrected, by applying the correction-coefficient, to the fresh condition of the brain. The corrected average diameters have been tabulated in table 13 a (unpublished), compared respectively with the corresponding standard values for the brains of the same age, and condensed in table 13. The correction-coefficients which were used are given in table 12.

212

NAOKI SUGITA

TABLE 11

Giving for each litter group in this study the average hrain weight, the age, the computed cortical volume, the cell density and the computed number of cells in the entire cortex, as based on the observed measurements presented in this paper, each compared with the corresponding standard values for the same age. Standard values were taken from my previous presentation (Sugita, '18b). This table was condensed from an original full table 11a {unpublished) , which gives the data for each individual. At the end of the table the averages for the test and control groups are given.

TEST CONTROL

AVERAGE AGE

AVER AGE

BRAIN

WEIGHT

CORTICAL volume:

L.F X W.D X T

cell density:

N

CELL number: N XL.FX W.D XT

GEO UP

Starved

and control^

Standard

for the same age

Starved

and controls

Standard

for the same age

Starved

and controls

Standard for the same age

days

grams

mm J

OTTO. 3

Series I

A c, a, d, f

T.

I

7 —

0.584

134.4

151.8

437

375

482.9

450.8

h

T.

II

15

1.024

263.1

265.0

206

202

542.0

535.0

b, g

C.

I

8

0.688

159.9

165.0

355

354

452.4

467.5

i

C.

II

17

1.278

314.5

275.0

182

198

572.4

545.0

Series I

B a, c, e, f

T.

I

9

0.644

151.6

187.0

364

298

489.1

479.2

i

T.

II

19

1.052

287.7

285.0

194

191

558.1

544-0

b, d

C.

I

6

0.543

112.4

126.5

445

388

457.8

44s. 5

g, h, j

C.

II

18

1.144

285.5

278.3

184

195

526.2

543.3

Series I

C a, c, d

T.

II

20

1.105

287.3

284.7

182

191

521.6

542.0

b, e

C.

II

22

1.307

320.9

289.5

188

188

603.4

540.5

Series I

D a, c, d

T.

I

12

0.778

201.1

238.3

242

213

486.4

505.3

e

T.

II

18

1.089

278.7

280.0

199

195

554.6

546.0

b

C.

I

9

0.870

214.4

207.0

245

230

525.3

476.0

Series I

E b, c, d

T.

I

12

0.867

210.3

249.3

238

207

497.1

516.7

g, h

T.

II

20

1.122

295.9

290.0

194

188

574.0

545.0

e, f

C.

II

17

1.179

278.0

272.5

195

197

535.9

535.0

GEOWTH OF THE CEREBRAL CORTEX

213

TABLE n— Continued

TEST CONTROL

AVERAGE AGE

AVER AGE

BRAIN

WEIGHT

CORTICAL VOLUME

L.F X W.D X T

CELL density:

N

CELL number:

NXL,FX

W.D X T

GROUP

Starved

and controls

Standard for the same

Starved

and controls

standard for the same

Starved

and controls

standard for the same

age

age

age

days

grams

rnm.^

mm.^

Series II

Fa, b

T.

I

13

0.832

218.7

252.5

260

206

550.4

520.0

c-1

T.

II

25+

1.204

307.9

SOS 4

178

180

548.7

545.7

Series III

Ga-g

T.

I

11 +

0.844

213.2

229.1

248

225

520.4

504.1

h-j

T.

II

22

1.154

302.2

294.7

189

186

570.3

546.7

Average 1

T.

I

11

0.758

188.2

218.0

298

254

504.4

496.0

(Ser. I-III)/

T.

II

20

1.107

289.0

286.1

192

190

552.8

543.5

Average 1

C.

I

8

0.700

162.2

166.2

348

S24

478.5

^62.3

(Ser. I) /

C.

II

19

1.227

299.7

278.8

187

195

559.5

541.0

By comparing the corrected values in the underfed with the standard values, the average diameters of the cell body and of the nucleus in the underfed brains are found to be generally smaller, on the average, by 9.8 per cent (cell body by 8.6 per cent and nucleus by 11.0 per cent) than the standard value. At the end of the following table 13 appears a summary of the comparisons, arranged as in the earlier tables in this study.

As seen in this summary, both the pyramids and the ganglion cells are much retarded in development in size of the cell body in the underfed brains weighing less than 1.0 gram or of ages under sixteen days, the average diameters of the cell body being 11.5 per cent (in the pyramids 11.2 per cent and in the ganglion cells 11.8 per cent) smaller than the standard for the same age. But in the underfed brains weighing more than 1.0 gram, this arrest in size-development of nerve cells is no longer so notable, the average diameters of the cell body being smaller than the standard by only 5.7 per cent (in the pyramids by 8.3 per cent and in the ganglion cells by 3.1 per cent). The size of the

214

NAOKI SUGITA

TABLE 12

Giving for each litter group in. this study the average brain iveight, the correctioncoefficient, and the observed {not corrected) diameters (transverse and longitudinal) of the cell body and the micleus of the pyramids (in the lamina pyramidalis) and of the ganglion cells (in the lamina ganglionaris), measured at locality VII in the frontal section. This table was condensed from table 12a (tin published) for individual cases. The averages for the test and control groups are given at the foot of the table

m

% o

o

CO < X

k2

<

■z

o

K S

LAMINA PYRAMIDALIS

LAMINA GANGLIONARIS

SERIES, LITTER AND

Cell body diameters

Nucleus diameters

Cell body diameters

Nucleus

diameters

>

s 2

C

q

>

e

03

H

bl 13 O

a

OJ

■a

J

>

1

M

a o

grams

M

M

M

M

li

M

n

Series I

A c, a, d, f

T.

0.584

1.18

11.5

17.2

10.5

11.2

14.8

22.4

13.0

15.6

h

T.

II

1.024

1.28

14.2

19.5

13.3

15.1

19.8

29.2

17.2

19.8

' b, g

C.

0.688

1.14

14.1

19.0

12.9

14.3

18.2

25.8

16.1

18.2

i

C.

II

1.278

1.26

15.2

22.0

14.1

15.5

20.1

30.5

18.0

20.1

Series I

B a, c, e, f

T.

0.644

1.17

13.3

18.8

12.0

13.5

17.2

25.3

16.0

17.5

i

T.

II

1.052

1.37

14.0

20.4

13.4

15.7

19.5

28.3

17.4

19.6

b, d

C.

0.543

1.09

13.9

18.0

12.4

13.6

18.6

24.1

15.6

17.0

g, h, j

C.

II

1.144

1.31

14.7

20.8

14.4

15.4

19.9

30.3

18.3

19.6

Series I

C a, c, d

T.

II

1.105

1.25

14.6

21.3

13.9

14.3

18.8

29.9

17.7

19.3

b, e

C.

II

1.307

1.16

16.0

21.1

14.4

15.3

19.9

30.4

17.8

19.6

Series I

D a, c, d

T.

0.778

1.24

14.3

19.4

12.9

13.8

17.6

27.7

15.4

17.2

e

T.

II

1.089

1.28

14.0

20.0

12.2

14.0

18.3

28.8

16.2

19.4

b

C.

0.870

1.11

16.1

19.8

14.5

15.8

21.1

27.2

18.2

19.8

f

C.

II

1.220

1.14

14.9

21.5

14.2

14.8

19.2

28.6

17.2

18.0

Series I

E a, b, c, d

T.

0.835

1.23

13.5

19.8

12.8 14.3

17.9

28.3

16.0

18.2

g, h

T.

II

1.122

1.26

14.0

20.7

12.5 14.2

19.7

30.7

16.5

18.1

e, f

C.

II

1.179

1.21

15.1

21.7

13.9 15.4

19.2

30.6

17.6

19.2

GROWTH OF THE CEREBRAL CORTEX

215

TABLE 12— Continued

o

|i

<

n

w -< K

« 2

fa

m

u

z

e^

K H

§5

LAMINA PYRAMIDALI8

LAMINA GANGLIONABIB

SERIES, LITTER AND GROUP

Cell body diameters

Nucleus diameters

Cell body diameters

Nucleus diameters

>

C

2

M

C! O

1-1

>

a S

s o

>

c

C

o

>

H

bC

C

o

grams

M

M

M

M

M

M

M

Series I7

F a, b

T. I

0.832

1.21

14.8

19.7

13.6

14.7

19.3

28.6

17.6

19.3

c-1

T. II

1.204

1.32

14.9

21.0

13.7

14.8

19.0

30.0

17.3

19.1

Series III

Ga-g

T. I

0.844

1.24

14.0

19.8

13.1

14.3

17.9

28.4

16.8

18.4

h-j

T. II

1.154 0.753

1.26

13.9

19.8

12.6

13.9

18.3

28.7

16.2

18.1

Average \

T. I

1.21

13.6

19.1

12.5

13.6

17.5

26.8

15.8

17.7

(Ser. I-III) /

T. II

1.107

1.29

14.2

20.4

13.1

14.6

19.1

29.4

16.9

19.1

Average |

C. I

0.700

1.15

14.7

18.9

13.3

14.6

19.3

25.7

16.6

18.3

(Ser. I) /

C. II

1.226

1.22

15.2

21.4

14.2

15.3

19.7

30.1

17.8

19.3

nucleus is much more affected by the underfeeding than that of the cell body. In the underfed brains of T. I groups the average diameter of the nucleus is smaller by 13.9 per cent (in the pyramids by 15.3 per cent and in the ganglion cells by 12.5 per cent) and in those of T. II groups it is smaller by 8.0 per cent (in the pyramids by 11.0 per cent and in the ganglion cells by 5.1 per cent) than the standard for the same age. The deficiency in the average diameter of the cell body by 6 to 12 per cent and that of the nucleus by 8 to 14 per cent correspond to the inferiority in volume of about 20 to 45 per cent and 25 to 50 per cent, respectively.

On the other hand, in the control brains of all weights, the size of the cell body and of the nucleug have proved to be also somewhat smaller than the standards, but the deviations are not so much in comparison with the underfed, the deficiency in the average diameters of the cell body and the nucleus being on the average 5.3 per cent (table 13).

216

NAOKI SUGITA

TABLE 13 Giving for each litter group in this study the average age, brain weight, the corrected average diameters of the cell body and the nucleus of the pyramids {in the lamina pyramidalis) and the ganglion cells {in the lamina ganglionaris), based on the condensed data in table 12, each compared with the corresponding standard values for the same age, taken from my former presentation {Sugita, '18c.) This table was condensed from table Ida {unpublished) for individual cases. The averages for the test and control groups and their percentage relations are given at the end of the table, {per. diff.) = percentage difference

TEST CONTROL

H O <

m o <

> <

» <

a

B

m o <

> <

L.\MIN.\ PYR.A.MID.\.L1S

L.\MIN.\*G.\NGLION.\^RIS

SERIES, LITTER AND

Cell body Aver, diameter

Nucleus Aver, diameter

Cell body Aver, diameter

Nucleus Aver, diameter

1 1

!:

o O

u

■a

a

o3

s

u

-d

a B

m

T3 01

a

S 02

days

grams

M

M

M

M

J"

M

M

M

Series I

Ac, a, d, f

T.

7 —

0.584

16.6

19.4

13.3

16.6

21.6

25.9

16.8

20.7

h

T.

II

15

1.024

21.1

23.7

18.1

19.8

30.6

31.3

23.6

24.4

b, g

C.

8

0.688

18.7

19.6

15.4

16.9

24.7

26.7

19.5

21.2

i

C.

II

17

1.27

23.1

23.8

18.7

20.0

31.2

31.3

2 .1

24.4

Series I

B a, c, e, f

T.

9

0.644

18.4

20.7

14.8

17.8

24.3

27.9

19.4

22.1

i

T.

II

19

1.052

23.2

24.0

19.8

20.0

32.1

31.4

25.1

24.5

b, d

C.

6

0.543

17.4

18.5

14.3

15.8

23.3

24.9

17.8

19.8

g, h, j

C.

II

18

1.144

23.1

23.9

19.7

20.0

32.4

31.3

25.0

24.4

Series I

C a, c, d

T.

II

20

1.105

22.1

23.9

17.6

20.0

29.7

31.4

22.9

24-4

b, e

C.

II

22

1.307

21.4

24.0

17.4

20.0

29.1

31.5

21.8

24.5

Series I

D a, c, d

T.

12

0.778

20.6

22.9

16.6

19.5

27.4

30.1

20.2

23.8

e

T.

II

18

1.089

21.4

23.9

16.8

20.0

29.5

31.3

22.8

24.4

b

C.

9

0.870

21.8

22.1

18.4

18.8

29.3

28.4

23.2

23.0

f

C.

II

22

1.220

22.4

24.1

18.2

20.1

29.5

31.6

22.1

24.5

Series I

E a, b, c, d

T.

X2

0.835

19.8

23.0

16.4

19.8

27.1

30.9

20.7

24-2

g, h

T.

II

20

1.122 21.5

24-0

16.8

20.0

31.0

31.4

21.7

24.5

e, f

C.

II

17

1.179 22.0

23.7

17.7

19.9

29.5

31.3

22.4

24.5

GROWTH OF THE CEREBRAL CORTEX

217

TABLE n— Continued

TEST CONTROL

O <

> <

s

z

a o m o <

LAMINA PYRAMIDALIS

LAMI.VA GANGLIONARIS

SERIES, LITTER

Cell body Aver, diameter

Nucleus Aver, diameter

Cell body Aver, diameter

Nucleus Aver, diameter

1

6

S

5

O

3

1

o

Q

-a c 5

o

■E

-0

a

dans

grams

ij

M

At

M

M

M

Series II

F a, b

T. I

13

0.832

20.8

2S.2

17.1

19.8

28.5

31.1

22.3

H.4

' c-1

T. II

25+

1.204

22.9

23.9

18.6

20.0

31.0

31.5

23.6

H.4

Series III

Fa-g

T. I

11 +

0.844

20.6

22.5

17.0

19.2

27.9

29.9

21.9

23.5

h-j

T. II

22

1.154

21.0

24.1

16.7

20.1

29.0

31.5

21.7

24.5

Average

(Ser. I-III)

T. I

11

0.753

19.5

22.0

15.9

18.8

26.1

29.3

20.2

23.1

(per. diff.)

(-11.2)

(-15.3)

(-11.8)

(-12.5)

Average

(Ser. I-III)

T. II

20

1.107

21.9

23.9

17.8

20.0

30.4

3H

23.1

24.4

(per. diff.)

(- 8.3)

(-11.0)

(- 3.1)

(- 5.1)

Average

- (Ser. I)

C. I

8

0.700

19.3

20.1

16.0

17.2

25.8

26.7

20.2

21.3

(per. diff.)

(- 3.8)

(- 6.7)

(- 3.2)

(- 5.1)

Average)

(Ser. I)

C. II

19+

1.226

22.4

23.9

18.3

20.0 30.3

31.4

23.1

24.5

(per. diff.)

(- 6.2)

(- 8.5)j

(- 3.3)

(- 5.5)

It is also seen that by underfeeding the nucleus is more affected than the entire cell body both in the pyramids (deficiency in diameters; T. I groups: cell body 11.2 per cent and nucleus 15.3 per cent, T. II groups: cell body 8,3 per cent and nucleus 11.0 per cent) and in the ganglion cells (deficiency in diameters; T. I groups: cell body 11.8 per cent and nucleus 12.5 per cent, T. II groups: cell body 3.1 per cent and nucleus 5.1 per cent) of brains of all weights, while the pyramids are more markedly affected than the ganglion cells both in the cell body (deficiency in diameters on the average of T. I and T. II groups: pyramids 9.8 per cent and ganglion cells 7.5 per cent) and in the nucleus (deficiency

218 NAOKI SUGITA

in diameters on the average of T. I and T. II groups: pyramids 13.2 per cent and ganglion cells 8.8 per cent). In young brains which weigh less than 1.0 gram, the influence of the underfeeding is considerable, while in brains weighing more than 1.0 gram or of ages more than sixteen days we can not detect any large arrest in the size-development, especially of the ganglion cells (the sizes of the cell body and the nucleus of the ganglion cells in the T. II groups are quite equal to the corresponding sizes in C. II groups) (tables 12 and 13). These observations are in agreement with the conclusions reached by Morgulis Til).

13. PERCENTAGE OF WATER IN BRAIN

As stated earlier (in chapter III), Litter H in Series II, in which a young primipara mother was entrused with seventeen young in order to produce a series of underfed young, was used partly for the investigation of the percentage of water in the underfed brain and partly for a histological study of myelination (not considered at this time).

In this Series II the development in brain weight is not so greatly arrested, as compared with the arrest in body growth, as in Series I. As already shown, in Litter F, which was treated in a similar manner, the brain weight is on the average 9 per cent low, but in this Litter H it has been possible to arrest the brainweight growth on the average by about 12 per cent, compared with the standard of the same age (compare table 4) .

Table 14 gives for each individual examined in this litter the sex, the age, the brain weight, and percentage of water in the brain, each accompanied by the standard percentage of water contained in the brains of the same age and sex and also of the same weight and sex. The differences are given in special columns.

By obtaining averages, it is found that the underfed brain contains slightly (0.48 per cent) more water, when compared with the normal brain of the same age and somewhat (1.4 per cent) less water, when compared with the normal brain of the same weight. This means in terms of the percentage of water.

GROWTH OF THE CEREBRAL CORTEX

219

TABLE 14

Showing for each brain in litter H the sex, the age, the brain weight, and the percentage value of water in the brain, accompanied with the standard values of percentage of water in brain for the same age and for the same brain weight. The differences between the observed percentages and the corresponding standard values are given in special columns, ivith their averages. *

NO.

.SEX

AGE IN

D.\ys

BRAIN WEIGHT

PERCENTAGE OF WATER

BRAIN OBSERVED

PERCENTAGE OF

WATER

STANDARD FOR THE

PERCENTAGE OP

WATER

STANDARD FOR THE

Same age

Difference in observed

Same brain weight

Difference in observed

grams

H a

f

13

0.880

86.39

85.^0

+0.99

86.82

-0.43

b

f

17

1.024

84.15

83.82

+0.33

85.08

-0.93

c

f

23

1 . 135

82.00

81.93

+0.07

83.21

-1.21

d

f

28

1.166

80.83

80.74

+0.09

82.70

-1.87

e

m

32

1.215

80.31

80.04

+0.27

81.70

-1.39

f

f

37

1.101

80.12

79.55

+0.57

83.78

-3.66

g

m

43

1.295

80.24

79.32

+0.92

80.56

-0.32

Averag

e

+0.48

-1.40

that the underfed brain is shghtly underdeveloped for its age, but somewhat overdeveloped for its weight. Similar relations have been revealed by the comparisons already made. Normally about 0,5 per cent excess in percentage of water in the brain would mean at the early ages approximately one or two days' retardation in development (compare table 74 in 'The Rat/ Donaldson, '15).

From the same litter (Litter H) I took with each of the above individuals a second rat for the study of the myelination, because it is known that the percentage of water in the brain is correlated with its myelination. The brains under seventeen days of age showed no fibers in the frontal sections, as stained with PalKultschitzky method. The twenty-eight-day brain showed only a few faintly stained fibers in the cortex, the fibers in the corona radiata (designated C. E. by Watson, '03) being already myelinated. Material above thirty-seven days was not examined. This passing examination of a small number of cases roughly indicates, therefore, that the first appearance of myelina

220 NAOKI SUGITA

tion in somewhat retarded, because, according to the investigation of Watson ('03), myelination in the corona radiata should have begun at eleven days and radiations into the cortex should have been recognized at twenty-four days. But a more detailed test for this j5rocess is required before any special use can be made of the results.

14. RELATIVE QUANTITIES OF THE ALCOHOL EXTRACTIVES

In my former paper (Sugita, '17 a) a chart, based on the data given in 'The Rat' (Donaldson, '15), was presented to show the absolute quantity of sohds contained in the Albino brain according to the brain weight. For comparison with this, I calculated also the relative quantity of alcohol-extractive substances in the Albino brains, as shown by comparing the initial weight of the brain with its weight after extraction by 80 per cent alcohol (for twenty-four hours) and 90 per cent alcohol (for twenty-four hours) according to a uniform procedure. As the brains were treated uniformly throughout the investigation, the results are comparable among themselves.

The results from 120 normal albino rat brains, grouped in twenty brain-weight groups (Groups I to XX), are given here in table 15 and plotted also in chart 1, in which the smooth curve (in a dotted line) represents the percentage weight of the extracted brain on the fresh brain weight. In chart 1, the graph which presents the absolute amounts of solids (in grams) according to the brain weight is also given in a solid line based on the chart in my former paper (chart 12, Sugita, '17 a). It was remarked previously (Sugita, '17 a) that in the Albino brains weighing between 0.95 gram and 1.4 grams, that is, between ten and thirty-five days of age, the rate of increase in solids is somewhat higher than in the periods before and after that phase, and this fact was formerly interpreted as indicating that, during this phase, the myelination in the brain had been proceeding very actively. This interpretation is now supported by the graph which gives the percentage weight of the brain. This graph varies inversely to the amount of the alcohol-extractives

GROWTH OF THE CEREBRAL CORTEX

221

and, as it decreases relatively rapidly in the phase during which the brain grows in weight from 0.9 gram to 1.35 grams, or in the ages between nine and thirty-three days, it shows that during that phase the alcohol-extractives increased.

The turning points in the both graphs marked with crosses X and XX) and asterisks (* and **), respectively, are in fair

•/n

"•r

500

78

!.

"■■—

-...

y

400

74 72

--.'.._

. ~

c

>

^

y

^v

\

^

'^

iou

68 66 64 62 60

1

/

/-'

i'i"

•

200

!

/

•

1

^

^

)00

-^

^

-^^

i

Q2 0.3

0.5 Q6 QT

09 10 \\ i.2 13 1.4 1.5 1.6 1.7 1.8 19 2.0 W

Chart 1 The dotted line shows the ratio between the initial brain weight and the weight after its dehydration and extraction in 80 per cent alcohol (for twentyfour hours) and 90 per cent alcohol (for twenty-four hours) according to a uniform procedure, plotted on the brain weight. The data were taken from table 15. The graph was drawn connecting the middle points of each pair of entries, and ** indicate the turning points in the graph.

The solid line shows the absolute weight of the solids in the brain according to the brain weight. The data were taken from table 74 in 'The Rat' (Donaldson, '15) and calculated by me. * and ** indicate the turning points in the graph.

For the ratios of brain weight the scale is given on the left side of the chart and for the absolute weight of the solids the scale is given on the right side.

coincidence, so that it may be concluded that the mass of the alcohol-extractives would be in proportion to the grade of myelination in the brain, and by following the former the progress in myelination could be estimated roughly.

It must be emphatically stated that my figures given in table 15 do not represent the total quantity of the alcohol-extractives,

222

NAOKI SUGITA

TABLE 15

Giving for each brain-iveight group of the normal albino rat the average initial brain-weight in the fresh condition and the brain weight after dehydration and extraction in 80 per cent alcohol (for twenty-four hours) and 90 per cent (for twentyfour hours) by a uniform procedure. The ratio of the final brain weight to the ^initial weight is given in the last column as a percentage value. Based on observations on 120 albino rats, sexes combined.

BRAIN WEIGHT

BRAIN-WEIGHT GROUP

NUMBER OF CASES

BRAIN WEIGHT WHEN FRESH

AFTER

DEHYDRATION IN

80 AND 90

PER CENT ALCOHOL

RATIO TO THE

INITIAL BRAIN WEIGHT

gravis

grams

per cent

II (birth)

6

0.271

0.213

78.6

III

8

0.343

0.267

77.8

IV

9

0.428

0.332

77.5

V

14

0.543

0.416

76.7

VI

5

0.636

0.479

75.4

VII

4

0.755

0.571

75.7

VIII

10

0.844

0.630

74.7

IX (10 days)

5

0.954

0.714

74.8

X

6

1.047

0.757

72.3

XI (20 days)

5

1.161

0.820

70.6

XII

5

1.245

0.874

70.2

XIII

8

1.341

0.921

68.6

XIV

5

1.449

0.989

68.2

XV

7

1.558

1.074

68.9

XVI

8

1.667

1.131

67.9

XVII

6

1.721

1.170

68.0

XVIII (90 days)

5

1.832

1 222

66.7

XIX

1

1.924

1.317

68.4

XX

3

2.037

1.369

67.2

because the extraction was not complete. My figures are only by-products in a study on histological technique, and to obtain the total quantity of the extractives the brain must have stayed much longer in alcohol of a higher concentration. My data therefore give merely the relative values for the quantity of the alcohol-extractives, but are comparable among themselves and with the values from the underfed brains treated in the same manner.

In giving the ratio of the brain weight after extraction in alcohol (by this method) to its initial weight, no correction was made for the weight of water replaced by alcohol, because my object was

GROWTH OF THE CEREBRAL CORTEX 223

only to compare the results among themselves and not to determined the exact quantity of the extractive substances.

Table 16 gives for each group in this study the ratio of the brain weight after dehydration in 80 per cent alcohol (for twentyfour hours) and in 90 per cent alcohol (for twenty-four hours) to its initial weight in the fresh condition, calculated in the same way as in table 15 and each paired with the standard ratio for the same age, quoted from table 15. Thus compared, the underfed brains show in general a higher ratio, the difference amounts to 1.0-4.3 per cent, on the average 1.9 per cent, while the difference in the control brains is generally low, on the average + 0.4 per cent.

This examination tells us roughly that in the underfed brains the alcohol-extractives are somewhat less in quantity than in the normal brain, if the age be taken as the standard of comparison, and, therefore, it may be concluded that they are somewhat retarded in the formation of alcohol-extractive substances and therefore in myelination. Reviewing tables 14 and 16 together, we see that during underfeeding the myelination process or the increase in the alcohol-extractives is retarded slightly, but is going on, not greatly affected by the outside influence, regularly according to its age. It is fair to say, however, that the differences thus determined by extraction are seemingly less than those shown by the histological tests,

15. A DISCUSSION OX THE RELATION BETWEEN THE BODY

WEIGHT AND THE BRAIN WEIGHT IN THE UNDERFED

ALBINO RATS

By examining table 4 it will be readily seen that under severe underfeeding at an early age, the increase in the body weight and the brain weight, according to the age, is notably reduced, and, as a consequence, the acutely underfed (Series I, chapter 5 and table 1) have lost, in the course of first twenty days after birth (during suckling period), about 29 per cent in body weight, but only 8 per cent in brain weight, when compared with the corresponding standard values for the same age. By chronic starvation, during which the young (excessive in number) were left

224

NAOKI SUGITA

TABLE 16

Giving for each litter group in this study the average age, the initial brain weight in the fresh condition and the brain weight after extraction in 80 per cent alcohol {for twenty-four hours) and 90 per cent alcohol {for twenty-four hours) by a uniform procedure, and the ratio of the latter to the initial weight. The corresponding standard values for the same age loere calculated 07i the basis of the data in table 15 and compared with each arid the difference between them given as an average for each group. This table %uas condensed from table 16a {unpublished) for individual cases. The averages for the test andcontrol groups are given at the end of the table.

SERIES, LITTER AND

TEST CONTROL

AVERAGE AGE

AVERAGE BRAIN WEIGHT

AFTER EXTRACTION IN 80 PER CENT AND 90 PER CENT , ALCOHOL

standard ratio for the brain

of the same age

DIFFERENCE

GROUP

Final brain weight

Ratio to

the initial

brain

weight

FROM THE STANDARD

Series I

A c, a, d, f

b

b, g

i

T. I T. II

C. I C. II

days

715

817

gram.1

0.584 1.024

0.688 1.278

grams

0.450 0.779

0.517 0.928

per cent

77.2 76.0

75.7 72.7

per cent

75.7 72.8

75. li. 72.3

per cent

+ 1.5 +3.2

+0.3 +0.4

Series I

B a, c, e, f

i

b, d

T. I T. II

C. I C. II

919

6 18

0.644 1.052

0.543 1.144

0.488 0.799

0.414 0.826

76.1 76.0

76.4

72.2

74.9 71.7

76.1 72.1

+ 1.2 +4.3

+0.3 +0.1

Series I

C a, c, d

b, e

T. II C. II

20 22

1.105 1.307

0.816 0.934

73.9 71.5

72.9 71.8

+ 1.0 -0.3

Series I

D a, c, d

e

b f

T. I T. II

C. I C. II

1218

9 22

0.778 1.089

0.870 1.220

0.584 0.795

0.656 0.863

75.1 73.0

75.4 70.8

73.7 72.0

74.5 71.0

+ 1.4 + 1.0

+0.9 +0.2

Series I

Ea, b, c, d

e

T. I C. II

1213

0.835 1.024

0.626 0.760

75.0 74.1

73.7 73.4

+ 1.3 +0.7

Series II

F a, b

c-k

T. I T. II

13 25+

0.832 1.198

0.636 0.862

76.7 72.3

73.4 70.7

+3.3 + 1.6

GROWTH OF THE CEREBRAL CORTEX

225

TABLE IQ— Continued

SERIES, LITTER AND GROUP

TEST CONTROL

AVERAGE AGE

AVERAGE BRAIN WEIGHT

.AFTER EXTRACTON

IN 80 PER CENT AND

90 PER CENT

ALCOHOL

■n.- , Ratio to hr«i. the initial

Standard ratio for the brain

of the same age

DIFFERENCE FROM THE STANDARD

Series III

Ga-g

h-j

T. I T. II

days

11+

22

gra m s

0.844 . 1.154

gratnts

0.641 0.833

per cent

76.0

72.2

per cent

73.9

71.2

per cent

+2.1 + 1.0

Average \ (Ser. I-III)/

Average 1 (Ser. I) j

T. I T. II

C. I C. II

11+

20+

818+

0.753 1.104

0.700 1.195

0.571 0.814

0.529 0.862

76.0 73.9

75.8 72.3

74.2 71.9

75.3

72.1

+ 1.8 +2.0

+0.5 +0.2

continuously with the mothers (Series II and III, chapter 2 and table 2), the loss in the brain weight is relatively less, in some individual cases nothing, while the body weight suffers much more, compared with the acutely underfed groups (Series I).

The observed body weight and the brain weight of each individual in this study are plotted separately for each litter in chart 2, A to H, according to the advancing age. Comparing the set of graphs both for the body weight and the brain weight within every litter, it is clearly seen at a glance that the courses of the graphs are similar, so that one, which advanced in age but has a smaller body weight, has also a relatively smaller brain weight, and vice versa. From this it is concluded that, though the brain, with a strong impulse to grow, regularly increases in weight with age and is only slightly affected by outside influence, yet it is controlled somewhat by the growth in the entire body. Thus, within certain limits, the brain weight may be said to be a function of the body weight: a rat reduced in body weight by starvation has a brain also reduced in weight and, on the other hand, a rat excessive in body weight for its age, through overfeeding, has an exces'S of brain weight for its age, as seen in the control groups shown in table 4. In the interrupted starvation tests (Series I), an average reduction of 29 per cent in the body weight

THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29. NO. 3

226

NAOKI SUGITA

yns, yni

"-^

JTli

« 

,--y

^

-"

15 20 25 <J.

10 15 20 25 30 35 #0 ic^t

Chart 2 Giving for each litter in this study the relation between the body weight and the brain weight of the individuals. The capital letters for each small chart designate the litter. The data given in table 3 were plotted according to the advancing age in days. • ■ ' '— '• Observed body weight of the underfed, in grams. %

o o Observed brain weight of the underfed, in grams.

Observed body weight of the controls, in grams.

Observed brain weight of the controls, in grams.

For the body weight the scale is given on the left side and for the brain weight the scale is given on the right side of the chart.

GROWTH OF THE CEREBRAL CORTEX 227

is accompanied by 8 per cent reduction in the brain weight in the test rats, and an excess of 14 per cent in the body weight by an excess of 6 per cent in the brain weight in the controls. These relations indicate that the brain weight is affected in abnormal conditions of nutrition during early life so that its percentage is altered by about one-third the percentage of the change of the body weight, either plus or minus, as compared with the standard values. On the other hand, in chronic inanition (Series II and III) where the young rat is not disturbed, the brain-weight loss was also 8 per cent against a body weight loss of 39 per cent. It appears, therefore, that during the early helpless period the brain development is highly disturbed by the changes in the environmental conditions represented by removal from the nest, but that when the rats are not disturbed it is much less affected even by severe underfeeding.

Table 17 gives for each group in this study the brain weight — body weight ratio, in percentage value, paired with the ratio obtained from the corresponding standard values for the same age and sex, calculated on the data given in table 4. The complete data for each individual are contained in table 17 a (unpublished) from which table 17 was condensed. In the underfed the above ratios are all higher than the standard, as was to be expected, while in the controls lower ratios are sometimes seen, which, in turn, means an overgrowth of the body. The average differences for each litter and group are given and the values are indicative of the severity of starvation combined with the special characteristics of the litter. Within each litter the range of the differences is narrow but the evidence for this statement is furnished by the unpublished detailed table 17 a.

16. A DISCUSSION ON THE CHANGE IN SHAPE OF THE CEREBRUM

In my first paper (Sugita, '17) it was stated that the Albino cerebrum becomes relatively longer as the age advances. During starvation, the rate of increase in every dimension diminishes considerably, but the relations between the three dimensions remains nearly unchanged, so that, as a result, the underfed brain is somewhat elongated in shape in comparison with the standard

TABLE 17 Giving for each litter group in this study the average age, the sex, th

brain weight —

body weight ratio, compared with the same ratio for the standard rat of the same age and sex. The difference of the ratio for each group is given in the last column This table was condensed from table 17a (unpublished) for the indiAt the foot of the table the averages for the test and control groups

of the table, vidual cases are given.

SERIES, LITTER AND GROUP

TEST CONTROL

AVERAGE AGE

SEX

RATIO OF

BRAIN

WEIGHT TO

BODY

WEIGHT

The same

in standard

rat of the

savie age

DIFFERENCE FROM THE STANDARD

days

per cent

per cent

per cent

Series I

A c, a, d, f

T. I

7 —

1 m, 3 f

7.9

6.5

+ 1.4

h

T. II

15

a f

7.4

6.3

+ 1.1

b, e, g

C. I

8

3 m

6.4

6.8

-0.4

i

C. II

17

1 f

4.2

6.1

-1.9

Series I

B a, c, e, f

T. I

9

3 m, 1 f

8.7

6.7

+2.0

i

T. II

19

1 m

8.3

6.0

+2.3

b, d

C. I

6

2 f

7.6

6.5

+ 1.1

g, h, J

C. II

18

3 f

5.7

6.0

-0.3

Series I

C a, c, d

T. II

20

2 m, 1 f

7.7

5.8

+ 1.9

b, e

C. II

22

2f

5.3

5.6

-0.2

Series I

D a, c, d

T. I

12

1 m, 2 f

11.3

6.8

+4.5

e

T. II

18

1 m

8.4

6.2

+2.2

b

C. I

9

1 m

7.8

7.1

+0.7

f

C. II

22

1 m

5.1

5.6

-0.5

Series I

E a, b, c, d

T. I

12

3 m, 1 f

8.6

6.8

+ 1.8

g, h

T. II

20

2f

7,0

5.6

+ 1.4

e, f

C. II

17

Im, 1 f

5.6

6.4

-0.8

Series II

F a, b

T. I

13

1 m, 1 f

9.1

6.8

+2.3

c-1

T. II

25+

4 m, 6 f

7.5

5.1

+2.4

Series III

Ga-g

T. I

11 +

4 m, 3 f

10.3

6.9

+3.4

h-j

T. II

22

2 m, 1 f

9.3

5.5

+3.8

Average 1

T. I

11

9.3

6.8

+2.5

(Ser. I-III)/

T. II

21 +

7.9

5.8

+2.1

Average 1

C. I

8

7.3

6.8

+ 0.5

(Ser. I) /

C. II

19+

5.2

5.9

-0.7

228

GROWTH OF THE CEREBRAL CORTEX 229

brain, which is the same in weight but younger. As shown in table 5, in the underfed brains the measurement L.G (the sagittal diameter) is on the average nearly 2 per cent (about 0.25 mm. in a brain weighing 1.0 gram) greater. than the standard, while, on the other hand, as shown in table 6 a (unpublished), in the underfed the cortical thickness at the frontal pole (locality I) .which was measured almost in the same direction w^ith L.G is also greater by 10 per cent (about 0.25 mm. in a brain weighing 1.0 gram) than the standard for the same brain weight, while the cortex at the occipital pole (locality V) is nearly equal to the standard in thickness. Considering together the above facts, the sagittal length of the central nuclei only, if measured between the frontal and occipital poles, would be supposedly about the same in both the underfed and the standard brains weighing alike. On the other hand, the width W .B is, in the underfed, less by nearly 2 per cent (about 0.3 mm. for 1.0 gram brain) than in the standard, and the cortical thickness at locality VII, which was measured at the side of the cerebrum, is thicker in the underfed by nearly 10 per cent (about 0.4 mm. for the both hemispheres in a 1.0 gram brain (based on the unpublished table 6 b for each locality) , and therefore the central nuclei in the underfed are less in width by about 0.7 mm. (for a 1.0 gram brain) than the standard for the same brain weight. In short the central nuclei are notably elongated in shape in the underfed brain compared with the normal brain of like weight.

17. A DISCUSSION ON THE THICKNESS OF THE CORTEX IN THE

UNDERFED

As described in Chapter 7, the cortical thickness in the starved brain is on the average markedly greater than the standard for the same brain weight. In the sagittal sections, the locality I surpasses the standard most, the localities II and III are the next, while the localities IV and V are almost equal in thickness to the standard (these statements are based on the unpublished table 6 a for each locality). This order in which the localities surpass the standard in thickness is the same as the order in rate of increase in the cortical thickness during the post

230 NAOKI SUGITA

natal growth (Sugita, '17 a). The same statement is true for the iocahties VI, VII, and VIII in the frontal sections (based on the unpublished table 6 b). The order in the rate of increase in the cortical thickness is an index of the grade of intensity in cell migration to those localities and of the growth impulse of the elements there. From previous studies (Sugita, '17 a), it was found that, as a rule, the cortical thickness decreases from the frontal to the occipital pole and from the dorsal to the ventral aspect, and the nearer a locality is to the ventricular wall or the matrix the more rapid the rate of increase in the thickness of the cortex. In underfed brains, the localities which show normally the higher rate of increase in thickness are also greater in the cortical thickness when compared with the standard. So, in the underfed, the cerebral cortex is generally thicker than the standard for the same brain weight and thicker in each locality in proportion to the rate of increase in the thickness of that locality under normal conditions.

In short, the growth in the cortical thickness in the case of the underfed is more advanced than that of the normall brain of the same weight, which is, of course, younger.

18. A DISCUSSION ON THE RELATION BETWEEN CELL DENSITY AND THE COMPUTED VOLUME OF THE CEREBRAL CORTEX

As stated earlier, the cell density of the cerebral cortex, represented by the number of nerve cells in two unit volumes (N), is, in the underfed Albino brain, under sixteen days in age, considerably higher than the standard for the same age, and accordingly the cell size in the underfed must be smaller than the standard size and, by inference, the cell attachments also underdeveloped for the age. The relations between these data will be examined now according to my measurements as presented in this paper.

The cortical area as measured in the sections from the underfed brains proves to be slightly greater than the standard values for the same brain weight, but on the other hand, it is distinctly less in brains under sixteen days of age than the standard values

GROWTH OF THE CEREBRAL CORTEX 231

for the same age, which belong to brain weights higher by about 10 per cent.

Let us take as an example an underfed brain which weighs less than 1.0 gram for examination. The computed volume of the cerebral cortex is in the underfed smaller on the average by 16 per cent than the standard for the same age (chapter 9). As shown by calculation, the computed number of nerve cells in the entire cortex is almost the same in both the standard and the underfed, throughout all ages, so that the process of cell division appears to have been going on undisturbed by the condition of underfeeding. The cell density, the cell size, and the cortical volume must therefore be regulated so as to provide the cerebral cortex with the number of cells fixed according to the age, regardless of the starvation.

To present the relation, the formula A^ X L.F X W.D X T was used. The value. of iV X L.F X W.D X T has proved in my present material fro*n the underfed to have been 1,7 per cent higher than the standard, but as this is open to some correction, it may be regarded as approximately the same in both the underfed and the corresponding standard. To be less in the cortical volume, which was computed by the formula L.F X W.D X T, by about 16 per cent or more, the cell density must be increased by about 19 per cent or less theoretically. * This latter figure is fairly in accord with that obtained in my direct observation; that is, 17 per cent excess in the number of cells in a unit volume in the underfed brains (chapter 10). To be reduced in cortical volume by 16 per cent or more, the individual cell must theoretically be reduced in volume also in the same ratio, in order not to be reduced in total number. My results in cell-size measurement showed that the individual cells measured are reduced in average diameter by about 12 per cent, and accordingly in average volume by about 30 per cent or more. These figures appear somewhat higher than was to be expected, but it must be recalled that these figures apply only to the largest cells found in the measured locality, and this class of cells may suffer a disproportionate arrest, so that the figures do not indicate what has" taken place in the small cells and those of average size. Furthermore, in the

232 NAOKI SUGITA

cerebral cortex the neuroglia, the intercellular tissue and the blood-vessels occupy considerable space and these may not be reduced in volume in the same proportion as the large nerve cells. These facts combined seem to furnish an explanation why the largest nerve cells, which have been here studied, deviate somewhat in size from the figures theoretically to be expected.

The data here presented show, I think, that the relations betv/een the cell density and the cortical volume in the underfed fit with the formulas presented earlier and which represent the relations in the normal Albino brains.

19. A DISCUSSION ON THE PROCESS OF MYELIN ATION

Tables 14 and 16 supply the data on which the myelination process in the underfed Albino brain may be tentatively discussed.

In Donaldson's series ('11), which consisted of twenty-two litters of albino rats in which the underfeeding was begun at 30 days of age and in which all were killed after three weeks and compared with the controls from the same litter, the average brain weight of the underfed was 1 .402 grams and the percentage of water 79.28, while the average brain weight of the controls was 1.519 grams and the percentage of water 79.39. Here the underfed had 0.11 per cent less water. By examining the sections from the underfed and the controls, the author could not discover any recognizable difference in myelination between them. Hatai ('04) made a partial starvation experiment, extending over three weeks, using the albino rats in the growing stage, about thirty days old. In this series, the final average brain weight was 1.341 grams and the percentage of water 79.15 or 0.21 per cent less than in the controls from the same litter and killed at the same age and in which the final brain weight was 1.508 grams and the percentage of water 79.36. In the same series, the solids extracted with alcohol and ether were determined. The average amount c f the extractives in the test brains was 46.7 per cent, or 0.9 per cent more than in the controls, in which it was 45.8 per cent. Though higher in percentage in the underfed.

GROWTH OF THE CEREBRAL CORTEX . 233

the absolute mass of the extractive substances is 0.065 gram (about 5 per cent of the brain weight) less than in the controls of the same age. The absolute weights were in the underfed 0.626 gram and in the controls 0.691 gram. These extractives represent mainly the myelin which is contained in the sheaths of the nerve fibers, and the above results mean that the extractive substances are increasing at the same rate or slightly slower in the underfed than in the controls.

In my material as seen in table 14, the underfed brains contain slightly more water (by 0.48 per cent on the average) than the standard of like age, and, as presented above (chapter 13), the frontal section showed a higher percentage in area of the cortex against the area of the central nuclei, which latter contain the bulk of the mj'elin sheaths. On the other hand, the underfed brains contain less water (by 1.4 per cent on the average) than the standards of the same brain weight. Comparisons of the absolute weight of the solids in the underfed brain with the corresponding standard value for the same brain weight and for the same age, based on data in 'The Rat' (Donaldson, '15), are given in table 18. The underfed has shown as a rule considerably less in total solids than the standard for the same age, though it proved to be only slightly higher in percentage of water than the standard (also table 14). ■,

From the above, the absolute mass of the solids in the underfed brain seems to be more than in the standard for the same brain weight, but less than in the standard for the same age. So the increase in solid mass is somewhat retarded by starvation. It will be noted that in my series of rats the percentage of >vater in the underfed was 0.48 per cent above that in the standards of like age and this is the reverse of the results reported by Donaldson and by Hatai in the studies just cited. This discrepancy probably depends on the fact that my rats are absolutely much younger than those studied by the other authors, but the explanation must await further study.

Since, as shown in chart 1, the relative values of the quantity of the alcohol-extractives has a fixed relation to the absolute weight of the sohds in the brain, the above statement may be also

234

NAOKI SUGITA

TABLE 18

Giving for each individual in Litter H {Series II) the sex, the age, the observed brain weight, percentage of water, and the calculated absolute weight of the solids in the brain, compared with the standards for the percentage of water and the mass of solids for the brains of the same weight and of the same age. Averages are given in the last line.

STARVED

STANDARD

Sex

Age

Brain weight

Percentage of water

Mass of solids

For the same brain weight

For the same age

No.

Percentage of water

Mass of solids

Brain weight

Percentage of water

Mass of solids

H a b c d e f g

f

f

f

f

m

f

m

13 17 23 28 32 37 43

grams

0.880 1.024 1.135 1.166 1.215 1.101 1.295

per cent

86.39 84.15 82.00 80.83 80.31 80.12 80.24

grams

0.120 0.162 0.204 0.224 0.239 0.219 0.256

per cent

87.45 85.08 83.21 82.60 81.70 83.78 80.51

grams

0.110 0.153 0.191 0.203 0.222 0.179 0.252

0.187

grams

1.003 1.099 1.208 1.282 1.338 1.391 1.468

per cent

85.40 83.82 81.93 80.74 80.04 79.55 79.32

grams

0.146 0.178 0.218 0.247 0.267 0.285 0.304

Average

28

1.117

82.01

0.203

83.48

1.256

81.54

0.235

confirmed by the data given in table 16, in which it is clearly shown that in the underfed the alcohol-extractives are slightly less developed as compared with the standards for the same age.

20. SUMMARY

1. Young albino rats were experimentally starved throughout the suckling period, by one of the following methods :

Series I. Separation of the young from the nursing mother for the maximum time each day.

Series II. Entrusting one mother with an excessive number of young (over seventeen) at the same time and thus reducing the amount of milk for each young one.

Series III. Starving the nursing mother and thus reducing the quantity of milk secreted.

I employed five litters for Series I, two litters for Series II, and one litter for Series III; in all forty-six individuals were subjected to experiment and there were fourteen controls.

GROWTH OF THE CEREBRAL CORTEX 235

2. The underfed and the controls were killed at different ages (between three and forty days) and the body measurements and the brain weights recorded. The brain was fixed, sectioned, stained, and examined according to the standard procedure previously adopted for these studies (Sugita, '17, '17 a, '18 b, '18 c) and the size of the cerebrum, the thickness of the cerebral cortex, the area of the cortex in the sections, the number of nerve cells in a unit volume of the cortex, and the size of the pyramidal and the ganglion cells, were all determined and then corrected to the values for the fresh condition of the material, by the use of the correction-coefficients devised for these purposes.

Using these data, the relative volume of the cerebral cortex and the number of nerve cells in the entire cerebral cortex were computed, employing the formulas already devised by me (Sugita, '18 b). All the observed and computed data were compared with the corresponding respective standard values for the normal Albino brain of the same weight or of the same age, as given in my previous papers (tables 3, 4, 5, 6, 8, 11 and 13).

3. In Series I the underfed rats were found to be 29 per cent less in the body weight and 8 per cent less in the brain weight, than the standards for the same ages (between three and forty days). In Series II and III the underfed rats were 39 per cent less in the body weight while 8 per cent less in the brain weight. It appears from this that starvation without removal from the nest, and the corresponding disturbance to the young, retards the growth of the brain relatively less, despite the greater arrest in the body growth.

The underfed brain weight was found on the average 24 per cent higher than the standard for the same body weight. The brain weights in the underfed have values between the standards for the same age and those for the same body weight, but generally fall nearer to the former.

The brain weight is a function of the body weight : a rat which is more reduced in body weight by starvation has a more reduced brain weight. The brain weight — body weight ratio is always higher in the underfed than in the standard for the same age, and the difference between the ratios roughly indicates the severity of

236 NAOKI SUGITA

the starvation. Thus in those severely underfed the difference is higher than in those less severely underfed.

4. The shape of the cerebrum in the underfed is slightly elongated as compared with that of the standard with the same brain weight and approximates that for the same age. As the result of underfeeding, the growth of the central nuclei seems to be more arrested in width than in length and the changes in the growth in the cortex in thickness matter little for the shape of the cerebrum.

5. The thickness of the cortex is on the average 10 per cent greater in the underfed in the localities I, II, VI, and VII than in the standards for the same brain weight. By averaging according to the entire section, the average thickness in the sagittal section of the underfed exceeds that of the standard by 5.3 per cent and in the frontal section by 8.7 per cent. The general average thickness of the cortex in the underfed is consequently greater by about 7 per cent than the standard for the brain of the same w^eight. The locahties which normally show the higher rate of increase in thickness during the postnatal growth are those which are notably greater in the cortical thickness in the underfed brains.

6. The relative volume of the cerebral cortex, computed by the formula L.F X W .D X T, is generally smaller in the underfed than in the standard for the same age. In the underfed brains weighing up to 1.0 gram (that is, under sixteen days of age), it is on the average less by 16 per cent or more, while in the underfed brains weighing more than 1.0 gram it is 6 per cent greater than the standard. So it may be said that, in rats underfed severely, the cortical volume is considerably retarded in growth in early period of development, but this is somewhat compensated or overcompensated later when the brains attain the weight of more than 1.0 gram or in age of more than sixteen days.

7. The cell density in the cerebral cortex, represented by the sum of the number of pyramids in the lamina pyramidahs and the number of nerve cells in the lamina ganglionaris in two unit volumes of 0.001 mm.^, is considerably higher in the underfed than in the standard rat for the same age. The excess in cell

GROWTH OF THE CEREBRAL CORTEX 237

density in underfed brains weighing less than 1.0 gram is on the average 17 per cent, and that in underfed brains weighing more than 1.0 gram is almost equal to the standard for the same age. As in the underfed brains weighing less than 1,0 gram, the relative volume of the cortex is smaller than in the standard, it follows that the underfed brains, if they contain the same number of cells, must have a relatively higher cell density in a unit volume to balance the smaller total volume of the cortex.

8. The relative value of the computed number of the nerve cells in the entire cortex, calculated by the formula A^ X L.F X W.D X T, in the underfed was compared with the corresponding standard value for the same age and the former was found to be only slightly higher than the latter, so that they may be regarded as practically the same. If so, the process of the cell division in the cerebrum must have progressed according to the advancing age, in spite of the starvation.

9. The size of the nerve cells was studied on the pyramids in the lamina pyramidalis and on the ganglion cells in the lamina ganglionaris. The cell body of the pyramids in the underfed brains weighing less than 1.0 gram is smaller by 11.2 per cent in average diameter and that in brains weighing more than 1.0 gram smaller by 8.3 per cent than the standards for the same age. The corresponding figures for the nuclei of the pj^ramids are 15.3 per cent and 11.0 per cent.

The cell body of the ganglion cells in the underfed brains weighing less than 1.0 gram is smaller in average diameter by 11.8 per cent, and that in the underfed brains weighing more than 1.0 gram is smaller by 3.1 per cent than the standards for the same age. The corresponding values for the nuclei of the ganglion cells are less by 12.5 per cent and 5.1 per cent, respectively. So, on the average, the nerve cells in the cortex of the underfed of all weights are smaller in average diameter by about 9 per cent (for the underfed brains weighing less than 1.0 gram by about 12 per cent and for those weighing more than 1.0 gram only by about 6 per cent), and consequently smaller in volume by about 25 per cent than the standard cells of the same age. These determinations apply only to the largest cells found at the measured locality.

238 NAOKI SUGITA

10. The underfed brains (Series II) contain on the average sUghtly (0.48 per cent) more water, if compared with the normal brain of the same age, and somewhat (1.4 per cent) less water, if compared with the normal brain of the same weight. This means probably that, in terms of the percentage of water, the underfed brain is slightly underdeveloped for its age and somewhat overdeveloped for its weight. If the absolute weight of the soHd mass be calculated and compared with the standard for the same brain weight and sex, the solids are found to be somewhat more in the underfed and if the same compared with the standard for the same age and sex the solids are always less in the underfed. The relative value of the alcohol-extractives, obtained by comparing the initial brain weight with its weight after dehydration and extraction in 80 per cent alcohol (for twenty-four hours) and 90 per cent alcohol (for twenty-four hours) according to a uniform procedure, shows that in the underfed brains the amount of the alcohol-extractives is somewhat smaller than in the normal of the same age.

The above observations indicate that in thie underfed the myelination process in the brain is somewhat retarded for the age. This assumption was supported in a general way by the direct examination on the sections obtained from the underfed brains.

11. Briefly, we conclude that by starvation in the early days the brain suffers much in its development in toto, but the cell division is going on quite normally according to its age. The growth of the cells in size is retarded and the formation of myelinated fibers somewhat diminished by inanition. So the smaller weight and size of the underfed brain is due to an arrest in the growth and development of the constituent neurons and not to a decrease in their number.

GROWTH OF THE CEREBRAL CORTEX 239

LITERATURE CITED

Bechterew, W. von 1895 Uber den Einfluss des Hungerns auf die neugeborenen Tiere, insbesondere auf das Gewicht und die Entwicklung des Gehirns. Neurol. Centralbl., Bd. 14, pp. 810-817.

Chossat, Charles 1843 Recherches experimentales sur Tinanition. Memoire auquel I'Academie des Sciences a decerne en 1841 le prix de physiologie experimentale. Extrait des memoires de I'academie royale des sciences. Tome 8 des savants etrangers. Paris, Imprimiere Royal.

Donaldson, H. H. 1911 The effect of underfeeding on the percentage of water, on the ether-alcohol extract, and on medullation in the central nervous system of the albino rat. Jour. Comp. Neur., vol. 21, no. 2. 1915 The Rat. Memoirs of The Wistar Institute of Anatomy and Biology no. 6.

Falck, C. p. 1854 Beitrage zur Kenntnis der Wachstumsgeschichte des Tierkorpers. Virchow's Archiv, Bd. 7.

Hatai, S. 1904 The effect of partial starvation on the brain of the white rat. Amer. Jour. Physiol., vol. 12, no. 1.

1908 Preliminary note on the size and condition of the central nervous system in albino rats experimentally stunted. Jour. Comp. Near., vol. 18, no. 2.

1915 Growth of the body and organs in albino rats fed with a lipoidfree ration. Anat. Record, vol. 9, pp. 1-20.

Jackson, C. M. 1915 a Effect of acute and chronic inanition upon the relative weights of the various organs and systems of adult albino rats. Amer. Jour. Anat., vol. 18, pp. 75-116.

1915 b Changes in the relative weights of the various parts, systems and organs of young albino rats held at constant body weight by underfeeding for various periods. Jour. Exp. Zool., vol. 19, pp. 99-156.

Lasarew, N. 1895 Zur Lehre von der Veranderung des Gewichts und der zelligen Elemente einiger Organe und Gewebe in verschiedenen Perioden des vollstandigen Hungerns. Dissertation, Wasschau (cited by Miihlmann, '99).

Morgulis, S. 1911 Studies of inanition in its bearing upon the problem of growth. I. Archiv f. Entw., Bd. 32, Heft 2.

MtJHLMANN, M. 1899 Russische Literatur liber die Pathologie des Hungerns (der Inanition). Sammelreferat. Centralbl. f. allg. Pathologie, Bd.

10, pp. 160-220; 240-242.

SuGiTA, Naoki 1917 Comparative studies on the growth of the cerebral cortex. I. On the changes in the size and shape of the cerebrum during the postnatal growth of the brain. Albino rat. Jour. Comp. Neur., vol. 28, no. 3. 1917 a Comparative studies on the growth of the cerebral cortex.

11. On the increase in the thickness of the cerebral cortex during the postnatal growth of the brain. Albino rat. Jour. Comp. Neur., vol. 28, no. 3.

240 NAOKI SUGITA

1918 a Comparative studies on the growth of the cerebral cortex.

IV. On the thickness of the cerebral cortex of the Norway rat (Mus norvegicus) and a comparison of the same with the cortical thickness in the albino rat. Jour. Comp. Neur., vol. 29, no. 1.

1918 b Comparative studies on the growth of the cerebral cortex.

V. Part I. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal sections, of the albino rat brain, together with the changes in these characters according to the growth of the brain. Part II. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal sections of the brain of the Norway rat (Mus norvegicus), compared with the corresponding data for the albino rat. Jour. Comp. Neur., vol. 29, no. 2.

1918 c Comparative studies on the growth of the cerebral cortex.

VI. Part I. On the increase in size and on the developmental changes of some nerve cells in the cerebral cortex of the albino rat during the growth of the brain. Part II. On the increase in size of some nerve cells in the cerebral cortex of the Norway rat (Mus norvegicus), compared with the corresponding changes in the albino rat. Jour. Comp. Neur., vol. 29, no. 2.

VoiT, Carl 1866 t'ber die Verschiedenheiten der Eiweisszersetzung beira

Hungern. Zeitschrift fiir Biologie, Bd. 2. Watson, John B. 1903 Animal education. Con. from the Psychol. Lab.

Univ. of Chicago, vol. 4, no. 2, pp. .5-122.

ADTHOR S ABSTRACT OF THIS PAPER ISSUED BY THE BIBLIOGRAPHIC SERVICE, MARCH 30

COMPARATIVE STUDIES ON THE GROWTH OF THE CEREBRAL CORTEX

VIII. GENERAL REVIEW OF DATA FOR THE THICKNESS OF THE CEREBRAL CORTEX AND THE SIZE OF THE CORTICAL CELLS IN SEVERAL MAMMALS, TOGETHER WITH SOME POSTNATAL GROWTH CHANGES IN THESE STRUCTURES

NAOKI SUGITA

From The Wistar Institute of Anatomy and Biology

THREE FIGURES AND TWO CHARTS

I. INTRODUCTION

Years ago Schwalbe ('81) pointed out as characteristic somatic expressions, which might be taken to indicate the grade of intelhgence of a species of animals, the following four measurements on the brain: 1) total weight of the brain; 2) total number of nerve cells in the brain; 3) total area of the surface of the hemispheres of the brain, and 4) the thickness of the cerebral cortex. Since then he and many other neurologists have endeavored to gather data on the morphological evidence for the development of mental ability. Donaldson and Hatai ('The Rat,' Donaldson, '15) have made systematic observations on the growth changes in the central nervous system as well as in other organs and systems, using exclusively the albino rat. As a result of their investigations, the postnatal growth of the brain and the spinal cord, in gross measurements, and the relations of these to the other systems during growth have been determined. In line with these studies, I also made further researches on the growth in the thickness of the cerebral cortex, the size and shape of the cortical nerve cells and the relative number of the cortical cells in both the Norway and albino rats. The results of these researches have been already presented (Sugita, '17,, '17 a, '18, '18 a, '18 b, '18 c, '18 d), with references

241

THE JODRNAI, OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 3

242 NAOKI SUGITA

to some similar studies by other authors. These data give us a general idea of the postnatal development of the cerebral cortex in a representative mammal (albino rat), and we may fairly infer that similar changes occur in other mammals during the growth of the brain. To test how^ far my conclusions on the mode of the development of the cerebral elements during postnatal life may be extended, I shall review and summarize in the present paper the results obtained by several authors on the development of the cortex in other mammals and make a comparison of their results with the data obtained by me.

II. THICKNESS OF THE CEREBRAL CORTEX IN THE ALBINO RAT

The results obtained by me regarding the cortical thickness in the brain of the albino rat may be summarzed as follows (Sugita, '17 a):

1. The cortex at the frontal pole of the hemisphere is the thickest and that at the occipital pole is the thinnest. Speaking in general terms, the cortex diminishes in thickness from the frontal to the occipital pole and from the dorsal to the ventral aspect.

2. After birth, the general average of the cortical thickness increases very rapidly during the first ten days, thickening from 0.74 mm. at birth to 1.73 mm. at ten days, more than twice the thickness at birth, while the brain weight increases from 0.25 gram to 0.95 gram during the same period. This is designated by me the first phase of the cortical development.

3. Between the tenth and the tw^entieth day after birth, the cortical thickness increases more slowly, attaining at twenty days to within 4 per cent of the full thickness of the cortex, namely, 1.84 mm., or about 2.5 times the thickness at birth, while the brain weight increases to 1.15 grams. This is designated the second phase of the cortical development.

4. From the twentieth to the ninetieth day, the cortical thickness increases but little on the average, attaining at ninety days the thickness of 1.93 mm., or 2.6 times the thickness at birth, w^hile the brain weight has increased to about 1.80 grams. This is designated the third phase of the cortical development.

GROWTH OF THE CEREBRAL CORTEX 243

After the ninetieth day, there is no significant change in the thickness of the cortex, but the area of the cortex increases as the brain weight rises and at 2.0 grams is greater than at 1.15 grams (20 days) by about 45 per cent.

5. In the first phase the cortex increases its thickness by receiving some newly formed cells from the matrix and many already formed from the transitional layers and at the same time by the general enlargement of the neurons, especia ly the cell bodies; in the second phase, however, it grows main'y by the enlargement of the cell bodies and the growth of the axons and dendrites; while during the third phase it thickens only slightly, but extends in area as the result of the ingrowing axons and the formation of the myelin sheaths and non-nervous structures.

6. The cortex at the frontal pole increases its thickness very rapidly and steadily, continuing to do this even after the end of the second phase, while at all the other localities the cortex thickens in the same proportion, so that at the end of the second phase all the localities reach nearly the full thickness, but maintain their initial relations. The localities heterogeneous in their cell lamination show in the course of thickening some deviation from the localities which are typical.

7. The cortex generally attains nearly its full thickness before myelination, as shown by the Weigert staining method, occurs in it. In the Albino, the cortex has nearly its mature thickness at twenty days, just before the young rat is weaned and when the brain has attained only a trifle more than half its final weight. The growth of the cortex in thickness is therefore precocious.

III. INCREASE IN CORTICAL THICKNESS DURING GROWTH OF THE BRAINS OF THE MOUSE AND THE GUINEA-PIG

Mouse. Isenschmid ('11) has made a study of the cortical cell lamination in the brain of the mouse and given a map of the topographic localization in the hemisphere, which is reproduced here as figure 1. De Vries ('12) and Rose ('12) have also presented a brain map of the mouse according to their studies on the cell architecture of the cortex ; a map which resembles that

244

NAOKI SUGITA

[k

\

[■\ \w\

"^^l \

w

\\ '\

^•rm.

/ ^

1 i \

---~M°

e

/ i- "

^•^ oa|?

V,

^

/.--■■' ,'V

rA^

— f

Fig. 1 Cortical area of the mouse (Mus musculus) — reproduced from the original by Isenschmid ('11); the thickness of the cortex at each area designated on the map is tabulated in table 1 of this paper. Double lines show borders of three — the dorsolateral, the frontomedial, and the suboccipital — regions of the neopallium. Shaded parts (areas t, s, and h) do not lie in the same (median) plane as the other areas. A = Dorsal view of the right hemisphere; B = Lateral view of the right hemisphere; C = Medial view of the right hemisphere. B.olf. = Bulbus olfactorius; C = Corpus callosum; c.A. = Cornu Ammonis; cl. = Claustrum; s.;?. = Septum pellucidum. s — s' = the level corresponding to that from which the sagittal sections of the Albino brain were taken by me; /— /' = the evel corresponding to that from which the frontal sections of the Albino brain were taken by me; h — h' = the level corresponding to that from which the horizontal sections of the Albino were taken by me.

GROWTH OF THE CEREBRAL CORTEX

245

TABLE 1 Giving for each localiUj of the brain of the adult mouse the characteristics of the cell lamination, the thickness of the cortex on the slide as deterinined from the photograms given by Isenschmid {'11), and the relative thickness of the outer and inner layers as presented by the same author. For the localities consult figure 1 in this paper, which was reproduced from the original of Isenschmid {'11)

AKEA

(fig. 1)

CHARACTERISTICS OF. THE AREA IN CELL-LAMINATION

e

f

i

k

1

m

r

q

s t

Largest ganglion cells contained (18 X 20 m)- Not so large cells

IV layer thick

Transitional part

Paleopallium

IV layer not so well developed

Adjoins to fovea limbica, cell lamination not clear

Transitional part (ganglion cells: 13 X 15 m)At the corner (ganglion cells: 12 X 14 /u)

(Ganglion cells : 15 X 18 m)

Similar to area q

THICKNESS OF THE CORTEX

0.73

0.86 0.50 0.53

0.62 0.44 0.81 0.78 0.71-0.61 1.201 0.56 0.26 0.34

RELATIVE

THICKNESS OF

THE OUTER AND

INNER LAYERS

OF THE

CORTEX

outer: inner'

48:52

45:55 45:55 45:55

42:58

34:66 23:77

22:78 28:72

1 Section cut obliquely.

^ The outer layer = the lamina granularis externa plus the lamina pyramidalis plus the lamina granularis interna. The inner layer = the lamina ganglionaris plus the lamina multiformis.

of Isenschmid. Isenschmid ('11) has recorded the thickness of the cerebral cortex of the mouse on the sHde at every locahty mapped in his figure (fig. 1). But the actual thickness not being given explicitly for each locality, I calculated the values from the direct measurements made on the photograms. The brain was fixed in alcohol, imbedded in paraffine and cut in 10-micra sections and stained with kresyl- violet. The thicknesses of the cortex on the slide as thus obtained are given for each locality in table 1 and also are condensed in table 2, in which the data

246

NAOKI SUGITA

TABLE 2

A com'parison of the thicknesses of the cerebral cortex at several corresponding localities in the albino rat and in the mouse. The data for the albino rat were taken from table 11 in ?ny previous paper (Sugita, '17 a, p. 578) and the data for the mouse were taken from a paper by Isenschmid {'11). The order of increasing thickness is the same in both animals

ALBINO RAT

MOUSE

Locality

Average

thickness of

cortex by

locality

Corresponding locality

Thickness of cortex at each of the localities

Average

thickness of

cortex by

locality

mm .

mm.

mm.

V and XIII

1.24

C

0.50

0.50

IV

1.42

d

0.53

0.53

XII and VIII

1.67

e and i

0.65 and 0.44

0.55

III and XI

1.91

a and e

0.73 and 0.65

0.69

VI

2 01

1 (corner)

0.78

0.78

II and X

2.03

k and b

0.81 and 0.86

0.84

VII

2.29

b

0.86

0.86

I and IX

2.99

frontal pole

1.00

1.00

Average

1.94

Average

0.72

for the Albino are so entered that the cortical thicknesses at the corresponding localities in the two forms may be compared. The order of the localities is arranged according to the increasing thickness in the Albino (taken from table 11, Sugita, '17 a, p. 578). The average value of the cortical thickness in the mouse is, on the slide, 0.72 mm., and if corrected to the fresh condition would probably be somewhat thinner than one-half the average thickness of the Albino cortex. The order of the thickness according to localities is quite the same, so that in both forms the cortical thickness decreases from the frontal to the occipital pole and from the dorsal to the ventral aspect. Moreover, the cortex at the frontal pole is the thickest and has double the thickness of that at the occipital pole.

As seen in figure 1, the cerebral hemisphere is divided by Isenschmid into three main regions — the dorsolateral, frontomedial and suboccipital regions — separated by the double line in figure 1.

The average cortical thickness in the dorsolateral region (fig. 1 a) is 0.56 mm. at its hinder-medial part and 0.90 mm.

GROWTH OF THE CEREBRAL CORTEX

247

at its fore-lateral part, and in this region the lamina zonalis is about one-twelfth, the main outer layers (the lamina granulans externa plus the lamina pyramidalis plus the lamina granulans interna) about two-fifths and the main inner layers (the lamina ganglionaris plus the lamina multiformis) about one-half the total thickness of the cortex. In the frontomedial region (fig. 1 c) the cortical thickness at the frontal pole is 1.00 mm. and that at the caudal part is 0.35 mm., while in the suboccipital region the cortical thickness ranges between 0.2 and 0.3 mm.

o o

I II

in

IV

vr

B 3J^4 6 7% 3Va \Va 17 M

Fig. 2 Showing diagrammatically the thickness of the cerebral cortex at locality a in the mouse at different ages. Reproduced from the original given by Isenschmid ('11). B = at birth. M = at maturity. The other arable numbers show the age in days. I = lamina zonalis; II = lamina granularis externa; III = lamina pyramidalis; IV = lamina granularis interna; V = lamina ganglionaris; VI = lamina multiformis. The cell outlines found between the last two diagrams indicate the relative size and shape of the cells in each cortical layer.

Isenschmid has given also diagrams illustrating the growth in cortical thickness at locality 'a' (fig. 1 a, corresponding approximately to locality III in my study, fig. 2, Sugita, '17 a, p. 525), sampled from material at several different ages and magnified uniformly. These are also reproduced here as figure 2. The diagrams show that as age advances the lamina pyramidalis (II and III) thickens steadily and continuously while the lamina

248

NAOKI SUGITA

ganglionaris (V) and especially the lamina multiformis (VI) grow much less rapidly. Chart 1 gives a comparison of the increase in the cortical thickness at corresponding localities (locality 'a' of the mouse and locality III of the albino rat) in the albino rat and the mouse, the data being from Isenschmid ('11) and Sugita ('17 a). In the Albino the cortex attains nearly its full thickness at twenty days (weaning time), while in the mouse this stage was reached between twelve and seventeen days of age, very closely corresponding to the weaning time of

mm. 2.0r

18

16

lA

J.2

1.0

0.8

0.6

0.4

Q2

1

■ —

.

AlbinocortexJocIH.

J

/^

/

\/

/

/

/

^^

-^

-^

B 2, 4 6 8 iO 12 14 16 18 20 22 24- 26 28 30 AgeindaysL

Chart 1 Giving the cortical thickness of the albino rat and of the mouse according to age. The data for the albino rat are taken from Sugita ('17 a) at locality III measured on the sagittal section and the data for the mouse are taken from Isenschmid ('11) at locality 'a.' These two localities approximately correspond.

the mouse, which is fifteen days. The remarkable phase during which the rapid increase in cortical thickness takes place in the Albino (first ten days after birth) cannot be clearly identified on the graph for the mouse cortex. It must be recalled, however, that data on the mouse cortex have not been corrected for the action of the reagents, while the data for the rat have been so corrected. The outstanding fact, however, is that the cerebral cortex in both forms attains nearly its full thickness just before the weaning time.

GROWTH OF THE CEREBRAL CORTEX 249

Guinea-pig. I have had the opportunity at The Wistar Institute to examine the sections of the guinea-pig brains prepared by Allen ('04) for her study on the myelination of the nervous system of that animal. The sections were cut in series in the frontal plane from material fixed in Miiller's fluid, imbedded in celloidin and stained by Weigert's method for the myelin sheaths. The thickness of the cerebral cortex in the adult guinea-pig (body weight, 618 grams; brain weight not recorded) is on the average 1.90 mm. (1.80 mm., 1.88 mm,, and 2.01 mm., respectively, at the localities corresponding to localities VI, VII, and VIII examined by me on the frontal section of the Albino brain at the level of the commissura anterior). The corresponding measurements at birth (body weight, 108 grams) are 1.71 mm. (and 1.51 mm., 1.75 mm., and 1.86 mm., respectively) and those at thirty-five days (body weight, 250 grams) are 1.85 mm. (and 1.77 mm., 1.86 mm., and 1.92 mm., respectively). So, from birth on to the maturity, the cortical thickness has on the average increased only 11 per cent. According to Allen, the guineapig at birth is covered with hair, has complete muscular development, and is almost independent of the mother, the central nervous system being practically completely myelinated, whereas, by contrast, the albino rat is born quite naked, extremely helpless and undeveloped, and myelination in the brain has not begun. The guinea-pig is psychically mature soon after birth (three days after birth) ; the degree of development of the central nervous system of the new-born guinea-pig corresponds to that of the albino rat at twenty-three to twenty-seven days or its period of first psychical maturity. A new-born guinea-pig is fobnd to have a cerebral cortex in which the myelination is going on.

Comparing the sections from the guinea-pig brain with those from the albino rat brain, it appears that the new-born guinea-pig corresponds to the albino rat of about ten days in cortical thickness, but seems to be older when judged by the myelination of the cortex. This coincides with observation that the guineapig is, almost from the start, relatively independent of the mother.

250 NAOKI SUGITA

IV. THE CORTICAL THICKNESS AT SEVERAL LOCALITIES IN THE BRAINS OF SOME MAMMALS OTHER THAN THE RAT

Few papers have been published regarding the differences in the thickness of the cerebral cortex at given localities of the brain in mammals other than the rat, except for man. Yet even in these cases, the techniques of hardening, imbedding, and staining used by the different authors are dissimilar and their results are accordingly not precisely comparable. Despite this, however, it has seemed worth while to make a survey of the data at hand.

Rabbit. Bevan Lewis (^81) has given as the natural thickness^ of the cerebral cortex of the adult rabbit the following figures (table 3) according to localities. For the localities, the map made by him and reproduced by me in a previous paper (Sugita, '17 a, fig. 10, p. 544) should be here consulted. He has presented the thicknesses of every layer of the cortex separately, but here only the total cortical thicknesses, as computed by me from his data, are given in round numbers.

Pig. Lewis ('79) has also determined the cortical thickness at several localities in the pig brain (the names of the localities

TABLE 3

The thickness of the cerebral cortex of the rabbit, quoted from Bevan Lewis {'81)

Depth of cortex on a plane with genu of corpus callosum :

mm.

Gyrus fornicatus 1.72

Sagittal angle 2.23

Extra-limbic 2.81

Near limbic sulcus 2.31

Depth of cortex on a jilane with posterior border of corpus eallosum:

Gyrus fornicatus 1 . 70

Sagittal angle 1.91

Extra-limbic 2 . 46

Depth of cortex of the modified lower limbic t3'pe 2.23 to 2.47

Depth of cortex in the cornu Ammonis:

Anterior regions 2 . 27

Average at six different sites 2 . 23

1 Lewis measured the cortical thickness on sections cut by the freezing microtome from fresh material and then hardened by osmic acid, stained by aniline black and mounted in Canada balsam. According to his statement we obtain, by this method, the natural depth o"" the cortex, no shrinkage occurring if the preparations have been carefully made (Lewis, '78).

Limbic lobe <

Upper parietal convolutions <

Lower parietal convolutions.

GROWTH OF THE CEREBRAL CORTEX 251

TABLE 4

The thickness of the cerebral cortex of the pig, quoted from Bevan Lewis {'79)

Depth of cortex from before backward:

mm.

'4.97 4.48 3.70 4.98 3.53 3.77

Average 4.22

fa. 28 2.65 3.08 3.91 4.23 3.44

Average 3 .50

■3.44 3.91 3.95 3.35 3.02 3.67

Average 3.64

are analogous to those given for the rabbit brain, loc. cit.)- His results are summarized in table 4. These values are distinctly high compared with those for other mammals, as shown in the various tables in this paper. These results taken together with those for the rabbit just given, which are also noticeably high, suggest that the determination by Lewis are for some reason systematically too high.

Marsupials to man. Table 5 is quoted (slightly modified) from Brodmann ('09) and gives for several species of mammals, including man, the cortical thickness at six localities (areae precentralis, frontalis, parietalis, occipitaUs, hippocampica et retrosplenialis) in the brain of each animal. The sections were made by hardening the material in 4 per cent formaldehyde, imbedding in paraffine, and staining by the modified Nissl's method, and the cortical thickness was measured by the micrometer directly on the slide. The average thickness was calculated by me for the four areas, excluding the areae hippocampica et retrosplenialis which are heterogeneous in cell lamination.

252

NAOKI SUGITA

TABLE 5

The cortical thickness at the corresponding parts of the cerebral hemisphere in different mammals, quoted from Brodmann i'09). According to his nomenclature, area precentralis = type 4, area frontalis agranularis = typed, area parietalis = type 7, area occipitalis = type 17, area hippocampica = type 28, and area retrosplenialis = type 29, as given in his 'Hirnkarte' {Brodmann, '09)

Homo sapiens (man) Cercopithecus (longtailed ape)

Lemur

Hapale (marmoset) .

Pteropus edwardsii (vampire bat). . . .

Erinaceus europaeus (hedgehog)

Cercoleptes caudivolvulus (kinkajou)

Lepus cuniculus (rabbit)

Spermophilus citillus (ground squirrel)

Macropus giganteus (kangaroo). .

grams

60,000

2,500

1,800

200

375 700

2,000

2,200

200

5,000

grams

1,400

85 23

7 3.5

10

2.2

3.0-4.5

3.0 2.3 2.15

1.9 1.87

2.17

2.7

2.1

2.8-3.1

O < 03 t^

3.0-3.8

2.5 2.3

2.17

1.6 2.1

2.0

2.33

2.18

3.08

2.0

1.67

1.73

1.7 1.78

1.7 2.2 1.73 2.2

2.3-2.6

1.7

1.55

1.26

1.76 1.5

1.9

1.37

1.9

mm.

2.5

1.6

1.35

1.14

1.52 1.6

1.9 1.2 1.13 1.7

< 2

2.3

1.1

1.19

1.07

1.4-1.76 0.8

1.67

0.8-1.5

0.75

1.2

3.0

1.95 1.73 1.59

1.66 1.61

1.89 1.79 1.54 2.15

Reviewing this table, it is readily seen that, within each order, the animal which has a greater brain weight shows also a greater cortical thickness, but a fixed relation between the brain weight and the cortical thickness has not been here revealed. In different orders, this relation is not true; the lemur and the kangaroo have a similar brain weight (23 to 25 grams),

GROWTH OF THE CEREBRAL CORTEX

253

while the cortical thickness in the latter is much greater (by about 25 per cent).

Prosimiae and primates. The following table (table 6) is summarized from a paper by Marburg ('12) and shows for some species of the prosimiae and primates the total cortical thickness measured at four representative localities (gyri centralis, frontalis, temporalis et occipitalis) . The average values were taken by me.

TABLE 6

Thickness of the cerebral cortex at several localities in monkeys, as presented by

Marburg {'12). Averages are calculated by me

Simla satyrus

Hylobates (sp.?)

Semnopithecus nasicus. . .

Macacus rhesus

Cynocephalus hamadryas

Ateles niger

Lemur varius

AVEI

CENTRAL, GYRUS

FRONTAL GYRUS

TEMPORAL GYRUS

OCCIPITAL, GYRUS

Of the four

localities

m »i .

7n7n .

7)1 711 .

mm.

mm.

3.11

2.97

2.43

3.78

3.24

2.51

1.78

2.83

3.78

2.43

2.43

1.35

2.50

"2.84

2.70

2.15

1.49

2.30

2.97

2.70

2.03

1.35

2.26

2.97

2.84

2.43

1.30

1.76

1.76

1.67

1.62

Of the three localities

2.84 3.18 2.88 2.56 2.57 2.75 1.61

This table also suggests that, in the order of monkeys, the average thickness of the cortex varies so that those which have the greater brain weight have also t|ie greater thickness of the cerebral cortex, but the brain weights are not available for comparison.

V. THE THICKNESS OF THE CEREBRAL CORTEX IN MAN

Man. There are scores of papers giving the measurements of the thickness of the cerebral cortex in man, but they are diverse in the techniques used for preparing the material, in the localities selected for measurement, and also in the manner of measurement. The results published before 1891 were all summarized by Donaldson ('91), but the table is not reproduced here as, owing to the lack of the information necessary for the interpretation of the values found, it has mainly an historical interest.

254

NAOKI SUGITA

Donaldson ('91) measured also the thickness of the cerebral cortex at fourteen localities from each hemisphere of nine normal brains (six males and three females), as shown in figure 3 reproduced from his original paper, in order to obtain control

Fig. 3 This figure shows the localities on the hemispheres from which the samples of cortex were taken by Donaldson ('91). For the thickness of cortex at each locality see table 8 and chart 2. A = Lateral aspect. 3 is used to designate the insula, here not exposed. B = Ventral aspect; C = Mesial aspect.

values for the study of the brain of a blind deaf-mute, Laura Bridgeman. The technique employed by Donaldson was fixation in bichromate and alcohol (potassium bichromate 2| per cent plus I its volume of 95 per cent alcohol) for six to eight

GROWTH OF THE CEREBRAL CORTEX

255

TABLE 7

Giving the average cortical thickness of man, arranged according to age and sex, together with the brain weight. Quoted from Donaldson {'91)

BRAI^f WEIGHT

AVERAGE CORTICAL THICKNESS

Males

years

grams

7nm.

35

1419

2.81

35

1443

2.98

39

1393

2.82

45

1367

2.92

57

1464

2.94

?

1210

3.11

Females

40

1196

2.74

45

1173

2.90

?

1312

3.07

Average

1331

2.92

weeks, washing in water for twenty-four hours, 95 per cent alcohol for two days, final preservation in 80 per cent alcohol, and imbedding in celloidin. The sections were cut about 100 micra thick and measured unstained under a low magnifying power with a micrometer eyepiece, at the summit of the gyrus arid at the side, midway between the summit and the bottom of the bounding sulcus. To obtain the average thickness at the locality, the smaller figure was multiplied by 2, added to the larger figure, and the sum divided by 3.

Table 7 shows the average thickness of the cortex (taken from the fourteen localities) arranged according to sex and age, quoted from Donaldson ('91). If we take the nine cases in this table as the basis for computation, we find the mean thickness of the cortex to be 2.92 mm., with a probable error of the mean equal to ±0.026 mm.

I wish to cite also the average thickness of the cortex, as thus obtained by Donaldson ('91), according to locality (table 8). These localities are shown in figure 3 and the relative thickness

256

NAOKI SUGITA

of the cortex at each is graphically presented in chart 2. Generally summarized, the average thicknes of the cortex of the adult man is 2.92 mm.; females have a slightly thinner cortex than males (differences less than 1 per cent, or 0.02 mm.) and the right hemisphere usually has a cortex a few per cent less thick than the left (maximmn difference 7 per cent).

With the foregoing determinations are to be compared the measurements by three other observers.

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Chart 2. -The curve was plotted according to table 8 to show the cortical thickness at each locality as measured by Donaldson ('91. The numbers placed by the ordinates indicate the thickness of the cortex in millimeters. The numbers for the localities are given below, and correspond to those in figure 3, A. B and C.

In accordance with this plan, the results obtained in a careful study by Hammarberg ('95) are tabulated in table 8. The material used for this study was a brain of a male, twenty-eight years old, mentally normal, and who died of typhoid fever. The technique employed was fixation in 95 per cent alcohol, imbedding in paraffine by means of xylol, sections 10 micra in

TABLE 8 Giving for several localities on the hemisphere of the adult human brain the thickness of the cortex, as measured by different authors. The general average thickness was taken, averaging all measurements presented by each author. For reasons given in the text, these averages as they stand are by no means comparable with each other. The data were taken from Donaldson ('91), Hammarberg {'95), Campbell {'05), and Brodmann {'08)

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Au/A-<jT

Tlanaldsan

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Cell

Cell

Fi ber

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2.70

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3.84

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3.93

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3.45

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3.09

3.4-0

2.A-0

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3.5 7

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2.50

3.sa

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2.98

3.00

3.34

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3.60

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3.17

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2.37

1. EZ

3.07

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su.f)e^ioT

2.3 7

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3.08

3.2.0

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2.93

2.SS

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2.4-3

2.50

2,0

3.3 5

3.n

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3.3 1

3.25

§ ^

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2.6/

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2.50

Z.5Z

2.. 6 8

2.8 3

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1. 4

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a.47

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2.65

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3. /O

2.64

Z.GO

2.4

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3.8 3

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3.3 5

3.80

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3.8 7

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2.67

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3.10

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2.60

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2,.94

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303

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3.48

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257

THE JOUBNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 3

258 NAOKI SUGITA

thickness and staining with methyleneblue. Hammarberg claims that after twenty-four hours in 95 per cent alcohol the brain piece shrinks about 20.5 per cent in volume and the cortical thickness diminishes by 0.1 to 0.2 mm., but that during the subsequent procedures no significant size changes occur. According to his results, the gyri frontales have the thickest cortex (about 3.0 mm.) and the lobus centralis or insula is the thinnest among localities typical in cell lamination. This latter part as measured by Donaldson shows the thickest cortex.

Campbell ('05) gave two series of determinations of the cortical lamination of the human brain, after cell staining and after fiber staining, represented by uniformly magnified illustrations of the sections at the several localities. Making use of his illustrations, I obtained a series of cortical thicknesses at different localities (table 8), reduced to the actual thickness on the slide, by dividing the direct measurement on the illustration by the magnification. His sections were taken from the material fixed in Miiller's or Orth's fluid and imbedded in celloidin, cut at 25 micra, and stained with thionine. The general average thickness thus obtained, the two series combined, is about 2.3 mm.

Brodmann ('08) also has measured the thickness of the cortex on the human brains at forty-two different localities on sections prepared by two different methods: one set was fixed in 4 per cent formaldehyde, imbedded in paraffine, and stained by Nissl's method for cell study, and the other, fixed in Miiller's fluid, imbedded in celloidin, and stained by Weigert's method for the myelin sheaths. His results, which are the averages from brains between seventeen and forty-five years in age, are also tabulated in table 8 for a comparison. The general average thickness given by Brodmann is about 3.09 mm.

Kaes ('07) also studied the growth in thickness of the human cerebral cortex, measured at twelve different localities on the hemisphere, using sections fixed in Miiller's fluid and stained by Weigert's method. His results are remarkably high, giving 4.9 mm. on the general average. His method of measuring the cortex is so arbitrary and peculiar, however, that his results are not included in this table 8.

GROWTH OF THE CEREBRAL CORTEX 259

Bevan Lewis ('79) has given as the average depth of the human cortex the figures as high as 4,84 to 5.70 mm., a higher vahie even than that of Kaes. His results for both the pig and rabbit cortex were also very high, compared with those obtained for other mammals. These results suggest that his technique, which he claims gives the natural depth of the cortex, is likely to produce very high values.

Reviewing the table (table 8) , the values for the cortical thickness given for a fixed part of the hemisphere by different authors are by no means in accord ; the results by Brodmann stand close to the results by Donaldson, while those given by Campbell are the lowest, less than one-half the values given by Lewis. These differences are probably due mainly to differences in technique and are not to be attributed to variations within the sanie species, as the series of Donaldson (table 7) and my previous study (Sugita, '17 a) both have shown that individual variations in cortical thickness, obtained by the use of the same technique, are low as compared with the variations for other body measurements.

On the average, the figures given by Donaldson and Brodmann are fairly close and the former being somewhat lower, probably because Donaldson took the average from the values at the summit and at the sides of the gyrus, while Brodmann has measured the thickness at the summit only. The figures given by Hammarberg and Campbell are low, probably owing to the shrinkage of the material during preparation, as may be inferred from the descriptions by the authors and from the studies on the effects of fixing fluids by King ('10) and by me (Sugita, '17 a, '18 b, '18 c).

Despite the apparent irregularity among the figures given for the cortical thickness at different localities by the several authors, as shown in table 8, there are some general relations which are fairly clear. If we examine table 9 in which has been entered for each region the average thickness obtained by each author, it may be safely said that this table (and also table 6 for the monkeys) shows that in man (and the primates) the cerebral cortex differs normally according to locality. The

260

NAOKI SUGITA

TABLE 9

Giving the average cortical thickness for several lobes and regions {with typical cell lamination) of the cerebral hemisphere as given by different authors, and the order of localities according to the cortical thickness, together with the difference in thickness between. the temporal and occipital regions. R = regio Rolandica, F = lobus frontalis, P = lobus parietalis, = lobus occipitalis, T = lobus temporalis. Based on table 8 in this paper

LOCALITY

DONALDSON

('91) (Cell)

HAMMARBERG

('95) (Cell)

CAMPBELL

('05) (Cell)

CAMPBELL

('05) (Fiber)

BRODMANN

('08) (Cell)

BRODMANN

("08) (Fiber)

Regio Rolandica

Lobus frontalis

Lobus parietalis

Lobus occipitalis

Lobus temporalis

mm.

2.92 2 92

2.59 3.21

mm.

2.34 2.92

2.43

2.09

2.49

mm.

2.43 2.46

2.44

2.16

2.64

77im.

2.21 2.15

2.13

1.96

2.29

mm.

2.74 3.50

3.17

2.47

3.48

mtn.

2.93 3.84

3.12

2.54

3.75

Average

2.91

2.45

2.43

2.15

2.92

3.16

Order of the above five localities as to the thickness

TFRO?

FTPRO

TFPRO

TRFPO

FTPRO

FTPRO

Difference between T and

0.62

0.40

0.48

0.33

1.01

1.21

frontal and temporal regions have in all cases the thickest cortex and the occipital region is the thinnest, while the position for the cortex of the parietal and Rolandic regions is less fixed. These thickness relations support the earlier statement made by me for the rat cortex that the thickness diminishes from the frontal to the occipital pole and from the dorsal to the ventral aspect.

Brodmann ('08) has concluded from his careful study that regional characteristics for the cortical thickness clearly exist. Diese sind in alien normalen Gehirnen gesetzmassig und kon

GROWTH OF THE CEREBRAL CORTEX

261

stant und bilden ein Hauptmerkmal der struktuellen Verschiedenheiten der Gehirnoberflache; jedes Strukturfeld besitzt demnach eine bestimmte, mittlere Durchschnittsbreite, durch welche es sich von den Nachbarfeldern auszeichnet." On the other hand, local variations within a fixed area are small, while individual differences between different brains for each locality may run sometimes as high as 0.5 mm. or more.

VI. INCREASE IN CORTICAL THICKNESS DURING THE GROWTH OF THE BRAIN OF THE MAN

From the point of view of the growth changes, there have been only few studies on the human cerebral cortex ever published. Kaes ('05, '07, '09), employing forty-one human brains (twentyeight males and thirteen females, normal and pathological combined) of different ages and of different grades of intelligence, studied the cerebral cortex for the purpose of following the growth changes in it. He took his sections from twelve localities in each hemisphere, stained the fibers by Weigert's method and measured the so-called cortical thickness from the ectal border of the Meynert's arcuate fibers (or fibrae propriae) to the ectal border of the zonal layer. His conclusions on the growth

^ His ('04) has given the following values as the cortical thicknesses measured at different localities of the hemisphere of the human embryos in early months, at different stages of intrauterine development- — measured directly on the sections imbedded in paraffine.

AGE OF EMBRYOS

AT CORPUS STRIATUM

M

AT LATERAL WALL OP THALAMUS

AT LATERAL

WALL OF HEMISPHERE (BASAL PART)

M

AT LATERAL

WALL OF

HEMISPHERE

(MID PART)

M

AT MEDIAN

WALL OF HEMISPHERE

AT BOTTOM OF

SULCUS CINGULI

M

1 2

50-55 65-75

4 5 6

7 8

150

360

800

1300

2000

130

160 300 600 900

300

400

110 120 130

170 200

90 110

130

60

50 40 30 30

262 NAOKI SUGITA

changes, briefly stated, are as follows: The average thickness of the cortex diminishes rapidly from his first entry (three months old, 5.58 mm.) to the twenty-third year (4.44 mm.) and is followed by an increase up to the forty-fifth year (5.71 mm.), where it is to be noted that the thickness attained is even greater than that at birth. Then it undergoes a second thinning up to the old age (at ninety-seventh year, his last entry, 4.62 mm.).

These conclusions have been disputed by Donaldson ('08) and by Brodmann ('09), and I am in agreement with these critics that Kaes' results cannot be taken seriously.

Brodmann ('08), in his paper on the cortical measurement, has noted only in a general way the average cortical thickness at the lateral surface of the hemisphere at several ages, as shown in table 10 (columns A and C). Nevertheless, these data can be used for a comparison.

Donaldson ('08) has compared the albino rat with man in respect to the growth of the brain and reached the conclusion that man and the rat show growth curves for the brain which are similar in form when the data are compared at equivalent ages, and the condition of the brain of the rat at five days of age is taken as like that of the human brain at birth. The relative growth rates of the rat and man are as 30 to 1 and the brain of the child at one year corresponds to that of the albino rat at seventeen days of age in its stage of development (Donaldson, MS.). These statements are also confirmed by me for the cortical thickness, as shown in table 10 (see below), and I have already noted that the transitional cortical cell layers, which are no longer to be seen in a new-born child, do not disappear in the albino rat until after four days of age (Sugita, '17 a, p. 539).

From these relations, we conclude that the course of growth in the thickness of the cerebral cortex in man and the albino rat would probably be similar, if the brains were compared at the equivalent ages. Such a comparison is attempted in table 10. Here the increase in cortical thickness in man and in the albino rat is compared, employing data given by Brodmann ('08) and by me (Sugita, '17 a). From the age (column A) given by Brodmann, the approximate brain weight (column B) was de

GROWTH OF THE CEREBRAL CORTEX

263

TABLE 10

Giving a comparison in the course of increase in cortical thickness in ynan and in the albino rat, according to data given by Brodmann {'08) and by Sugita {'17 a). Approximate brain weight in man and in the Albino for the equivalent ages were assumed in round numbers according, respectively, to Vierordt {'90) and Donaldson {'08)

A

B

C

D

E

F

G

MAN

ALBINO RAT

Correspond

Approximate

ing cortical

Observed

brain

Thickness

thickness in

Approximate

thickness of

weight, at the

Equivalent

of the cortex

human brain,

Age

brain

the cortex.

equivalent

(observed)

at ages

when the

weight

Brodmann

(observed)

age

given in

adult values

('08)

ages (Donaldson)

Column E

in the both are taken as the standards

grains

m m .

grams

days

mm.

7nm,

Fetus

8-9 months

1.0-1.5

Birth

0.80

1.25

Birth

380

1.5-2.0

0.50

5

1.10

1.75

1 year

950

2.0-3.0

1.10

17

1.75

2.76

Adult

1400

2.0-4.0

1.90

Adult

1.90

3.00

termined according to Vierordt ('90) and then the final weight (1400 grams) was entered corresponding to the adult brain weight of the albino rat (1.9 grains). The other corresponding brain weights of the Albino of the equivalent ages were entered also according to Donaldson ('08) (column D). The cortical thickness (column F) for the given brain weights of the Albino were then entered according to my former determination (Sugita, '17 a). If the cortical thickness of the adult man be assumed as 3.00 mm. (the mean value of 2.0 to 4.0 mm.) and the corresponding thickness at each age be calculated on the basis of the course of increase in cortical thickness in the Albino (given in column F), the results given in column G — a mere inference, to be sure — are fairly in accord with the figures presented by Brodmann (column C).

In this connection, I had the opportunity, through the courtesy of Dr. W. H. F. Addison, to prepare sections and examine the cortical thickness at the dorsal part of the gyrus centralis anterior (regio Rolandica) from a child thirteen months old (material hardened in 4 per cent formaldehyde, imbedded in paraf

264 NAOKI SUGITA

fine, and stained by Nissl's method). The mean value of the cortical thickness at the summit of the gyrus was 3.55 mm., or within 10 per cent the value obtained by Brodmann at the same locality in the adult brain and on a section similarly prepared and measured (table 8) . So far, then, as this observation goes, it helps to support my conclusion presented earlier that the human cortex has attained nearly its full thickness at the age of fifteen months (Sugita, '17 a).^

VII. THE BRAIN WEIGHT, THE CORTICAL VOLUME, AND THE BODY

WEIGHT

Dhere and Lapicque ('98) and DuBois ('98 a, '98 b), working independently, found several important relations existing between the body and the brain weights in man and a number of other vertebrates. Recently DuBois ('13) has obtained results which he has formulated in following terms:

1) In species of vertebrates that are alike in organization of their nervous system and their shape, but differ in size, and also in the two sexes of one and the same species, the quantity of the brain increases; A) as the quotient of the superficial dimension divided by the cube root of the longitudinal dimension. B) as the product of the longitudinal dunension by the square of its cube root.

2) In individuals of one and the same species and of the same sex, but differing in size, the quantity of brain increases as the square of the cube root of the longitudinal dimension of the body.

So, briefly stated, 1) reads: in any species of vertebrates that are equal in organization, in form of activity and in shape, the weights of the respective brains are proportional to the 0.55 power

' According to a study by Fuchs ('83), the child is born without any myelinated fibers in the cerebral cortex. In the lamina zonalis the first myelination appears at five months, in the lamina pyramidalis at the end of the first year, while in the innermost layers we see some faintly stained fibers at two months. The fibrae arcuate (association fibers) appear clearly at seven months. Later the myelinated fibers increase in caliber and number as the age advances, and at eight years they attain nearly the appearance which they have in the adult cortex.

GROWTH OF THE CEREBRAL CORTEX 265

of the weights of bodies, and 2) the exponent of correlation within the same species is for all vertebrates the 0.22 power.

These relations were based on a series of observations, and this illuminating idea is now generally accepted as true.

The brain in general consists of the white and the gray matter, and in higher animals the gray matter as represented by the cerebral cortex occupies a relatively large part of the entire cerebrum. This cortex is the seat of a complex series of physiological nerve centers, and the possibility that it has definite quantitative relations with the body as a whole is suggested by the following statement made by Du Bois ('13) :

If the quantity of brain does not increase proportionally to the volume of the body, exprassed by the weight, it might be that this is really the case with regard to the superficial dimension, as being proportional with the receptive sensitive surfaces and with the sections of the muscles, thus measuring the passive and active relations of the animal to the outer world, for which in this waj" the quantity of brain can be a measure.

This statement, to be sure, is applied by DuBois to the weight or volume of the entire brain, but if the volume of the cortex stands in some definite relation to the volume of the entire brain, then the cortical volume should be also in a definite relation to the size or weight of the body.

The cortica' volume is determined by the area of surface of the cerebral hemisphere and the thickness of the cortex. The former factor is not easy to determine exactly, even in lissencephala, while in higher animals the hemispheres have many convolutions which increase still further the difficulty of this determination. In lissencephala, the surface area of the hemispheres in two brains, which are nearly similar in the form of cerebrum, are approximately comparable with squares of the corresponding diameters of the cerebra.

The cortical thickness, on the other hand, is not so hard to determine exactly. The average thickness of the cortex in different mammals is given in table 11, quoted from various sources, and, as seen from this table, it is not directly related to the size or weight of the brain, since, as Marburg's ('12) table shows, the

266 NAOKI SUGITA

cortical thickness in several primates ranges within rather narrow limits (2.3 mm. to 2.8 mm.), while the brain weight shows a distinctly wider range (82 grams to 400 grams) (table 11). In some cases indeed the smaller brain has a thicker cortex, even in the same family (e.g., the smaller hapale has a thicker cortex than the larger lemur) . But in general we may conclude with Brodmann ('09) that, within one and the same order or family of mammals, the large brain tends to have a larger average value for the cortical thickness.

The relative cortical volume has been formerly computed by me, employing the formula especially devised for this purpose, in the albino and the Norway rat brains, so that the two forms may be compared directly (Sugita, '18 b). The ratio of the cortical volumes in the adult Albino (brain weight, 2.0 grams) and the Norway (brain weight, 2.3 grams) is 1.31, as the relative cortical volumes are, respectively, 393 and 517 (Sugita, '18 b, table 15), and the ratio of the body surfaces in the two animals amounts also to 1.30, when the body weights of the adult albino and the Norway rats are taken as 300 grams and 450 grams, respectively. Moreover, the ratio of cortical volumes in the two forms at any given age will prove to be almost equal to the ratio of body surfaces of the two at the same age.'*

As above tested, the body weight and the cortical volume of the animals in the same family stand in a definite relation, at least in this instance. But, as we cannot compute the volume of the cortex in other mammals from the data given in table 11, the relation can not be tested further.

■' For example, according to my former presentation (Sugita, '18 b), the computed cortical volume in the Albino Group XV (brain weight, 1.54 grams) is about 346 and that in the Norway Group N XVIII (brain weight, 1.83 grams) is about 423, and according to another determination (Sugita, '18 a) these two groups may be regarded nearly equal in age, as the Albino brain weight would be about 18 per cent less than the Norway brain weight of the like age. The ratio in cortical volume of the above two is 1.22. The body weight corresponding to the brain weight of 1.54 grams in the albino rat is 64 grams and that corresponding to the brain weight of 1.83 grams in the Norway rat is 90 grams ('The Rat,' Donaldson, '15). The ratio of the body surface in the above two, therefore, is about 1.25, quite near to the ratio in cortical volume.

TABLE 11 Giving for several species of mammals the adult body weight and brain weight, the average cortical thickness and the name of author from whom the data for the cortical thickness or for the brain and body weights were cited, arranged in the order of decreasing body weight within each family of inammals. The abbreviations of the names of authors are as follows: B = Brodmann {'09), I — Isenschmid {'11), L = Lewis {'79), M= Marburg, {'12), S = Sugita {'17 a, '18 a, MS.)

OF MAMMALIA

Rodentia

Chiroptera

Marsvipialia

Primates

Prosimiae

Artiodactyla f et Carnivo- \ ra I

Insectivora

NAME OF SRECIES

Simia satyrus (orang-outang).

Hylobates

Cynocephalus hamadryas

Macacus rhesus (macaques). . .

Cercopithecus (long-tailed ape)

Lemur varius

Lemur

Hapale (marmoset)

Microcebus

Ovis musimon (sheep)

Felis domestica (cat)

Erinaceus europaeus (hedgehog)

Talpa europaea (mole)

Lepus cuniculus (rabbit)

Cavia cobaya (guinea-pig)

Mus norvegicus (Norway rat) . Mus norv. albinus (albino rat) Spermophilus citillus (groundsquirrel)

Mus musculus (mouse)

Pteropus edwardsii (vampire

bat)

Vespertilio murinus (bat)

Macropus giganteus (kangaroo)

Didelphys

BODY WEIGHT'

7,350 950 920 356

2,500

2,170

1,800

200

62

23,000 3,000

700 75

2,200 600 450 300

200 20

375 23

5,000 1,100

BR.\IN WEIGHT'

grains

400.0

130.0

142.0

82.0

85.0

28.7

23.0

8.0

1.9

100.0 30.0

3.5 1.3

10.0 4.5 2.5 2.0

2.2 0.4

AVERAGE CORTICAL THICKNESS

7.0 0.3

25.0 5.5

mm. 2.8 2.8 2.3 2.3

2.3 1.6 1.7 2.0 1.5

1.6(2.6)2

1.5(2.6)2

1.8 1.0

2.2 1.9 2.1 1.9

1.8 0.8

1.7 0.4

2.3 1.2

K tS

fa p S <

M

M M M

B M B B B

L L

1 The body and brain weights of some animals were not given by the author who has given the cortical thickness. In such cases the body and brain weights were taken from the list given by Weber ('96).

2 According to Lewis (79), the values given here without brackets were taken from Meynert and show the value measured on the slide and the values given within brackets were obtained by his own observation and represent the natural depth of the cortex.

267

268 NAOKI SUGITA

VIII. SIZE AND GROWTH CHANGES IN SOME NERVE CELLS IN THE

^VIAMMALIAN BRAIN

Albino rat. The results obtained by me regarding the size and the growth changes of the pyramidal cells and of the ganglion cells in the cerebral cortex of the albino rat were summarized in a previous study (Sugita, '18 c). Four of the conclusions are here quoted:

1. The full size of the pyramids in the lamina pyramidalis is cell body 21 x 27 m and nucleus 18 x 20 /x in the fresh condition (on the slide, respectively, 16 x 21 ju and 14xl5yu). The full size of the ganglion cells in the lamina ganglionaris is cell body 27 X 37 M and nucleus 23 x 25 ^ in the fresh condition (on the slide, respectively, 21 x 29 ^ and 18 x 19 m) 2. The cell body and the nucleus of the pyramids attain their maximum size at twenty to thirty days in age. Up to ten days they still retain their fetal morphology. After having passed the maximum size at about twenty-five daj^s, they diminish somewhat in size, but the internal structure differentiates as the age advances.

3. The cell body and the nucleus of the ganglion cells attain nearly their maximum size at ten days, when they remain still in fetal form. After this stage, the size of the cell body still increases slowly but steadily as the age advances, while the nucleus remains nearly unchanged in size throughout life.

4. Taking a general view of the data already presented in this series of studies, it is very interesting to observe that the thickness of the cortex, the total number of the cortical nerve cells, and the size of the cortical cells, all attain nearly their full values at the same age of twenty days; that is, at the weaning time of the albino rat.

For comparison with these results on the cells of the cerebral cortex, there are some observations by Addison ('11) on the postnatal growth of the Purkinje cells in the cerebellar cortex of the albino rat. His material was also obtained from the rat colony at The Wistar Institute and the cerebellum was fixed in Ohlmacher's solution, imbedded in paraffine, and stained with

GROWTH OF THE CEREBRAL CORTEX 269

carbol-thionine and acid fuchsin. A part of his results on the Purkinje cells is here quoted:

The Purkinje cells are easily distinguishable at birth along the inner boundary of the molecular layer by their relatively large size and lightly staining nucleus. These cells measure 12 x 7 m and nuclei 8 X 6.3 At. During the first week, there is great increase in size of both nucleus and cytoplasm. The main bulk of the latter is at the ectal pole and from it several fine processes radiate into the molecular layer. At eight days the cells measure 18 x 12 /x and nuclei 10 x 8 ^ to 12 x 9 IX. At eight to ten days there is definite change in form by the elongation of the cytoplasm of the ectal pole to form the main dendrite, the previously existing fine processes becoming its branches. At the same time all the dendries become arranged in one plane, and this plane is parallel to sections directed across the folia. Nissl granules appear in the cj^oplasm at eight to ten days. The arrangement of Purkinje cells changes with the increase in the surface area of the cortex. At birth they are arranged in two to three irregular rows; at three days in one to two irregular rows, and at five days in one continuous row. As growth of the cortex continues, the space intervening between the Purkinje cells becomes greater. Some nuclei reach their maximum size of 12 x 9 /x at eight days, while the cell bodies usually continue to grow, reaching a maximum size of 24 x 19 ^ at twenty days. The dendrites reach the outer limiting membrane when all the outer granule eel's have migrated (twenty-one to twentyfive days), and continue to develop new branches until a much later period as is .diown by a comparison of cells from a 31 day with cells from a 110-day cerebelhun.

From this it is plain that the Purkinje cells (cell bodies) of the albino rat cerebellum have also reached full size at about the weaning time (twenty days of age) .

From the foregoing, we see that the functional cortical cells both in the cerebrum and in the cerebellum reach their full size at an early age — before the weaning time — and though they continue to mature after that they change only slightly in size, sometimes even diminishing. Thus the cortical nerve elements are all precocious in their growth, which is nearly complete when the young become independent of the mother and their education begins. Addison ('11) has stated also that the development of motor control in the young rat is closely correlated with the completion of the cerebellum and the rat attains its full motor control when the cerebellum has attained structural

270 NAOKI SUGITA

maturity at twenty-one to twenty-five days of age. At that age the cells are nearly full size. We may conclude, therefore, at least regarding some of the nerve cells, that the beginning of functional education of the cells at twenty days is preceded by the attainment of nearly full size, and after this period there is very little change in size, though the internal structures mature as the age advances.

Mouse. A study in this field was made by Stefanowska ('98) on the cortical cells of the mouse. She stained the cells by the method of silver impregnation and studied mainly the development of the cell attachments. Her conclusions may be condensed as follows:

1. In the new-born mouse most of the cortical nerve cells have a simple morphology. 2. The cells are usually arranged in chains, disposed perpendicularly to the surface of the cortex. 3. Besides these, there are some groups of cells more advanced in developmen and having many dendrites, and cells which have the adult form having many, long, ramified dendrites. 4. The different parts of the cortex do not attain the same degree of development at the same time. Some cell groups are more precocious. 5. In the lamina multiformis and in the lamina ganglionaris, we find always the most advanced cells in large numbers. 6. In the lamina pyramidalis the development of the cells is very slow. On the ectal surface, near the pia mater, many cells not at all differentiated are often found. 7. At one day after birth, the dendrites of cortical cells are covered with varicosities. The axis-cylinders have also many nodal swellings. 8, As the neurons develop, the varicosities become more and more rare. At fifteen days, varicosities are no longer seen on the dendrites and the neurons at this age have completed their development. 9. The appearance of the piriform appendices on the dendrites is somewhat delayed. At ten days all pyramidal cells show these appendices. These latter are the constant feature of the neuron, while the varicosities are only a temporary formation. The piriform appendices may be the terminal apparatus of the dendrites. 10. The piriform appendices are the last element which appears on the cortical cells during growth. This fact seems to suggest the high importance of these appendices for this nerve function.

As seen from the foregoing, the morphological completeness in respect of the dendrites and the axis-cylinder of the cortical cells is attained at fifteen days or at the weaning time of the mouse also.

GROWTH OF THE CEREBRAL CORTEX

271

TABLE 12 Giving for man and other mammals the size of the largest ganglioncells in the lamina ganglionaris of the cerebral cortex as presented by different authors. Data are arranged according to the order of the average diameters

NAME OF SPECIES

Homo sapiens (man)

Homo sapiens (man)

Homo sapiens (man)

Homo sapiens (man)

Felis leo (lion)

Felis tigris (tiger)

Cercoleptiis caudivolvulus (kinkajou).

Ursus syriacus (bear)

Indris (babakoto)

Felis domestica (cat)

Cercopithecus mona (African monkey)

Elephas (elephant)

Lemur

Mus norvegicus (Norway rat)

Ovis musimon (sheep)

Sus (pig)

Mus norvegicus albinus (albino rat) . .

Lepus cuniculus (rabbit)

Lepus cuniculus (rabbit)

Pteropus edwardsii (vampire bat)

Mus musculus (mouse)

MAXIMUM SIZE

REPORTED IN MICBA

Linear diameters

Average

diameter or

square root

of the

product

60X120

85

55X126

83

53X106

75

40 X 80

57

60X133

90

60X100

78

50X110

74

53X100

73

44 X 80

59

32X106

58

40 X 72

54

35 X 60

46

SOX 70

46

33 X 48

40

23 X 65

39

27 X 48

36

30 X 42

36

18 X 60

33

18X 40

27

16X 36

24

18X 20

19

Author

Betz Lewis Brodmann Hammarberg

Brodmann

Brodmann

Brodmann

Brodmann

Brodmann

Lewis

Brodmann

Brodmann

Brodmann

Sugita

Lewis

Lewis

Sugita

Lewis

Brodmann

Brodmann

Isenschmid

There are no other systematic investigations on the postnatal development of the cortical nerve cells in mammals, although there are some studies on the growth of nerve cells in the fetus, among which the researches by His ('04) (see footnote 2), Koelliker ('96), and Vignal ('89) are the most important.

Table 12 was compiled by me in order to compare the size of the largest ganglion cells in the lamina ganglionaris (the fifth layer of Brodmann) of the cerebral cortex of man and some other mammals. The tabulated data were taken from Brodmann ('09), Lewis ('79, '82), Hammarberg ('95), and others.

272 NAOKI SUGITA

The results obtained by me (Sugita, '18 c) in the albino and the Norway rats have been also entered.

IX. THE SIZE OF THE LARGEST CORTICAL CELLS IN MAN AND SOME OTHER MAMMALS

From table 12 we can draw only very general conclusions as to the significance of the size of the largest cortical cells. The giant Betz cells even in man vary rather widely in size according to the different authors, probably owing largely to the different technical methods used, as has been pointed out repeatedly in the course of this paper.

From time to time attempts have been made to formulate a general interpretation of the size of the Betz cells and of the nerve cells in general. From the examination of table 12, it is seen that the values for the mean diameters do not, except in the very most general way, follow the size of the animal, but that the Felidae, even the cat, stand high in the series.

We are not able to contribute any general explanation for the size of these cells, although it may not be out of place to repeat that in the Norway rat with the heavier brain these cells are larger than in the albino rat with the lighter brain (Sugita, '18 c), and so will merely call attention to the various authors who have had something to say in the matter: Lewis ("79), Hughlings Jackson ('90), Schwalbe ('81), Barratt ('01), Dunn ('00, '02), Herrick ('02), Donaldson ('03), Campbell ('05), Boughton ('06), Johnston ('08), and Kidd ('15).

X. Summary

1. In the present paper I have attempted to compare my conclusions regarding the development of the cortical elements in the brains of the albino and the Norway rats with the corresponding changes in other mammals. The data used for these comparisons were taken from various sources, but the comparisons are in many instances hampered by differences in technique or the lack of essential information.

2. The relations of the cortical thickness at different localities in the cerebrum are quite the same in the mouse and rabbit as in the rat. The development of the cortical thickness has proved to be similar in the mouse and guinea-pig: it attains nearly its full value at the weaning time of the animal.

3. The statement that the cortical thickness diminishes from the frontal to the occipital pole and from the dorsal to the ventral aspect probably holds true throughout mammals, including man.

4. The results given by different authors for the cortical thickness of human brain (averages or for each locality) are by no means in accord. Even for the same locality there are wide deviations. The best data indicate that the average cortical thickness of the adult human brain is about 3 mm.

5. The mode of increase in cortical thickness in man according to age appears to be similar to that in the albino rat, if the brains are compared at equivalent ages. The developmental stage of the brain of a new-born child corresponds to that of an albino rat of five days of age, and throughout the postnatal life the relative growth rate of the rat and man are as 30 to 1. The span of life 30 for man corresponds to 1 for the rat and the equivalent ages are represented by like fractions of the span of life. The human cortex probably attains nearly its full thickness at fifteen months, equivalent to twenty days of rat age.

6. The relative cortical volumes of the albino and the Norway rat brains, computed formerly by me (Sugita, '18 b), appear to be proportional to the surface areas of the entire bodies at the like age. This relation may be generally applicable within a given order of mammalia. The cortical thickness or the brain weight is in general only loosely correlated with the body weight or size of the animal.

7. The cortical nerve cells in the cerebruni and in the cerebellum of the albino rat are precocious in their growth, attaining almost the full size at twenty days, the weaning time. The maturation of the intracellular structures probably continues after the size is apparently completed. This process is shown also in the mouse.

8. The size of the Betz giant cells in the adult human cortex (found ill the gyrus centralis anterior) is reported differently by different authors. The mean value is about 75 micra in average diameter.

9. The size of the cortical cells, especially the Betz motor ganglion cells, of adult animals has no clear relationship to brain size or body size. These cells are notably large in the Felidae.

10. As a general conclusion to this series of studies the following statement may be made:

The morphological organization of the cerebral cortex is generally precocious. The size of individual cortical nerve cells, the total number of cortical cells, and the thickness of the cortex, all attain nearly their full values at the same time and very early in life (corresponding to the weaning time in some rodents) , after which the maturation of internal structures of the cell body and the nucleus continues. The brain weight and the cortical volume continue to increase even after this stage throughout the postnatal life, though not so rapidly as during the early period. This later growth is due principally to the development of the cell attachments, intercellular tissues (neuroglia tissue and bloodvessels), the ingrowth of axons into the cortex and their myelination, which together separate the cells from each other, and cause an increase in cortical volume. The cortical volume is primarily dependent on the size of individual cortical cells and their total number and it appears in animals belonging to a given zoological order to have a definite relationship to the size (or area of surface) of the body of the animal.

Literature Cited

Addison, VV. H. F. 1911 The development of the Purkinje cells and of the cortical layers in the cerebellum of the albino rat. Jour. Comp. Neur., vol. 21, no. 5.

Allen, Ezra 1912 The cessation of mitosis in the central nervous system of the albino rat. Jour. Comp. Neur., vol. 22, no. 6.

Allen, Jessie Blount 1904 The associative processes of the guinea-pig. A study of the psychical development of an animal with a nervous system well medullated at birth. Jour. Comp. Neur. and Psychol., vol. 14, no. 4.

Barratt, J. O. Wakelin 1901 Observations on the structure of the third, fourth, and sixth cranial nerves. Jour. Anat. and Physiol., vol. 35, p. 214.

BouGHTON, T. H. 1906 The increase in the number and size of the medullated fibers in the oculomotor nerve of the white rat and of the cat at different ages. Jour. Comp. Neur. and Psychol., vol. 16, pp. 153-165.

Brodmann, K. 1908 Uber Rindenmessungen. Centralbl. f. Nervenheilkunde u. Psychiatrie, Bd. 19.

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1918 b Comparative studies on the growth of the cerebral cortex.

V. Part I. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal sections of the albino rat brain, together with the changes in these characters according to the growth of the brain. Part II. On the area of the cortex and on the number of cells in a unit volume, measured on the frontal and sagittal sections of the brain of the Norway rat (Mus norvegicus), compared with the corresponding data for the albino rat. Jour. Comp. Neur., vol. 29, no. 2.

1918 c Comparative studies on the growth of the cerebral cortex.

VI. Parti. On the increase in size and on the developmental changes of some nerve cells in the cerebral cortex of the albino rat during the growth of the brain. Part II. On the increase in size of some nerve cells in the cerebral cortex of the Norway rat (Mus norvegicus), compared with the corresponding changes in the albino rat. Jour. Comp. Neur., vol. 29, no. 2.

1918 d Comparative studies on the growth of the cerebral cortex.

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