Paper - Comparative studies on the growth of the cerebral cortex 5 (1918)

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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.

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This 1917 fifth 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

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Comparative Studies on the Growth of the Cerebral Cortex

Prof. Naoki Sugita (1887-1949)
Prof. Naoki Sugita (1887-1949)

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

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

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 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

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 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.



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.


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


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

BRAIN 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 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 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


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

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

CORRECTION COEFFICIENT

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

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


BRAIN WEIGHT


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.


Table 6

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 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



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.



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.


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, 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, 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


Table 7

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, 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).


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.

V. Summary

1. Employing 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 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, 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 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 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

N. Area of the cortex in the sagittal section {Norway 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, 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






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.


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

BRAIN WEIGHT


OBSERVED

AREA 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

Table 9

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


CORRECTION COEFFICIENT


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


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


Table 10

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


Table 11

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

SAGITTAL 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).


Table 12

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


BRAIN


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 total 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,


Table 13

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.


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



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.


Table 14

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 CELLS


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

Norway 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 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.


Table 15

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 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 volume 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) .


Table 16

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


NORWAY RATS


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).


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.

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 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.

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.



Cite this page: Hill, M.A. (2021, June 24) Embryology Paper - Comparative studies on the growth of the cerebral cortex 5 (1918). Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Comparative_studies_on_the_growth_of_the_cerebral_cortex_5_(1918)

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