Anatomical and physiological studies on the growth of the inner ear of the albino rat 3 (1923): Difference between revisions
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==III. On the Growth of the Largest Nerve Cells in the Ganglion Vestibulare== | ==III. On the Growth of the Largest Nerve Cells in the Ganglion Vestibulare== | ||
Material and technique | |||
==Material and technique== | |||
The material used for the present study was in a great part the | The material used for the present study was in a great part the | ||
| Line 24: | Line 25: | ||
largest cells were taken from each part and the results averaged. | largest cells were taken from each part and the results averaged. | ||
Observations | ==Observations== | ||
By way of introduction I wish to say a word about equilibration | By way of introduction I wish to say a word about equilibration | ||
| Line 31: | Line 32: | ||
the head to and fro and roll over on the flanks, belly, or back. | the head to and fro and roll over on the flanks, belly, or back. | ||
While resting they take their normal position or lie on the side. | While resting they take their normal position or lie on the side. | ||
When turned on their backs they endeavor to regain the normal | When turned on their backs they endeavor to regain the normal position. The fore legs are of more use than the hind in making | ||
position. The fore legs are of more use than the hind in making | |||
readjustments. The tails hang down between the hind legs. | readjustments. The tails hang down between the hind legs. | ||
| Line 1,262: | Line 1,251: | ||
and therefore the ratio is 1 : 1.0. This increase in the cell bodies | and therefore the ratio is 1 : 1.0. This increase in the cell bodies | ||
is continuous from birth to old age, but after fifteen days is | is continuous from birth to old age, but after fifteen days is | ||
very slow. In the nucleus we see a slight increase at the earlier | very slow. In the nucleus we see a slight increase at the earlier ages, after which the values are nearly constant. This means | ||
ages, after which the values are nearly constant. This means | |||
that after birth the size of the cell bodies and their nuclei does | that after birth the size of the cell bodies and their nuclei does | ||
not increase so much as do those of the spiral ganglion cells, | not increase so much as do those of the spiral ganglion cells, | ||
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Wada T. Anatomical and physiological studies on the growth of the inner ear of the albino rat. (1923) Memoirs of the Wistar Institute of Anatomy and Biology, No. 10, Philadelphia. Rat Inner Ear (1923): I. Cochlea growth | II. Inception of hearing and cochlea growth | III. Growth of largest nerve cells in ganglion vestibulare | Final Summary | Literature Cited
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Anatomical and Physiological Studies on the Growth of the Inner Ear of the Albino Rat
III. On the Growth of the Largest Nerve Cells in the Ganglion Vestibulare
Material and technique
The material used for the present study was in a great part the same that was employed for the studies reported in chapter 1, with the addition of some new specimens as shown in table 114 and table 94. In the slides obtained in the radial vertical section we see the vestibular ganglion cells situated in a single group at the radix of the cochlea (Fig. 3 G. V.). As four ears were used in each age group, four cell groups were examined at each age. Besides these fourteen age groups, six rats used for cross-sections, in chapter 1, were also included.
The measurements were made in the same way and under the same conditions as those described earlier for the cells of the spiral ganglion. Since the ganglion vestibulare consists of two parts, the ganglion vestibulare superius and inferius, the ten largest cells were taken from each part and the results averaged.
Observations
By way of introduction I wish to say a word about equilibration in the young rat. The young just born crawl over on each other and seem to attempt to find the mothers nipples. They turn the head to and fro and roll over on the flanks, belly, or back. While resting they take their normal position or lie on the side. When turned on their backs they endeavor to regain the normal position. The fore legs are of more use than the hind in making readjustments. The tails hang down between the hind legs.
TABLE 114
Data on rats used for the study of the cells of the ganglion vestibulare (radial section).
See also table 94
AOB
BOOT
WEIGHT
BODY
LENGTH
BEX
BIDE
AUDITOHT
RESPONSE
days
grams
mm.
1
5
44
9
R.
4
44
9
R.
5
48
d 1
R. L.
3
9
60
<?
R. L.
8
56
9
R. L.
6
10
64
a
R.
10
64
9
R. L.
11
62
(7
R.
9
11
67
<?
R. L.
+
9
58
9
R.
10
57
tf
R.
12
13
70
d 1
R. L.
+
12
68
9
R.
+
15
72
c?
R.
+
15
13
74
d"
R. L.
+
14
75
9
R. L.
+
20
30
.96
d 1
R. L.
+
28
94
c?
R. L.
+
25
34
101
9
R. L.
+
34
100
d 1
R. L.
+
50
58
121
9
R. L.
+
43
104
(f
R. L.
+
100
146
176
c?
L.
+
103
154
9
L.
+
101
152
9
R. L.
+
150
154
184
9
R. L.
+
189
191
c?
R.
+
199
192
d 1
R.
+
260
137
162
9
R.
+
140
171
9
R. L.
+
134
178
9
R.
' +
367
205
202
rf
L.
+
170
182
9
L.
+
179
196
9
R. L.
+
546
282
222
d 1
R. L.
+
227
204
d 1
R. L.
+
At three days they move and crawl very actively. They tend to assume the normal position. When rolled over on the back or side they succeed in regaining the normal position in
158
ANATOMICAL AND PHYSIOLOGICAL STUDIES ON
a few seconds. When six days old the rats have fairly well coordinated movements. They use their fore and hind legs effectively and in the same way. When the mother 's body touches them they respond quickly by searching for the nipples.
At nine days they move much more quickly and the movements are well coordinated. .Though the eyes are still closed, they
TABLE 115
Diameters of the cells and their nuclei in the ganglion vestibulare in radial vertical section
(Chart 43)
AGE
BODY
WEIGHT
DIAMETERS IN M
CELL BODY
NUCLEUS
Long
Short
Computed
Long
Short
Computed
days
grams
1
5
21.2
19.5
20.3
12.4
11.1
11.7
3
9
23.7
22.2
22.9
12.5
11.6
12.0
6
11
24.0
22.1
23.0
12.3
11.9
11.9
9
10
24.8
23.0
23.9
12.5
11.6
12.0
12
13
24.9
23.0
23.9
12.5
11.7
12.1
15
13
24.8
23.0
23.9
12.5
11.6
12.0
20
27
25.0
23.3
24.1
12.3
11.6
11.9
25
34
25.2
23.6
24.4
12.5
11.8
12.1
50
50
25.6
23.6
24.5
12.5
11.6
12.0
100
112
25.5
23.9
24.7
12.8
11.9
12.3
150
174
25.4
23.5
24.4
12.8
11.6
12.2
260
138
25.8
23.4
24.6
12.4
11.7
12.0
367
184
26.2
24.9
25.5
12.9
11.8
12.3
546
255
26.5
24.2
25.3
12.8
11.8
12.2
Ratios 1
-367 days
1 1.3
1:1.1
1546 "
1.2
- 1.0
15367 "
1.1
- 1.0
crawl toward the object sought. When turned over on the back they regain the normal position immediately. While resting they lie on their bellies with all the legs spread well apart.
Twelve-day-old rats, though the eyes are still closed, go to and fro actively with good coordination, but are somewhat slower than the adults. The body loses its fetal red color through the development of the first hairs. After this period the rats do not differ greatly from the adult in their general behavior.
GROWTH OF THE INNER EAR OF ALBINO RAT
159
The growth changes in the ganglion cells of the ganglion vestibulare. In table 115 (chart 43) are given the values for the diameters of the cell bodies and their nuclei in the largest cells of the ganglion vestibulare. At the bottom of the last column for the cell body and for the nucleus, respectively, are recorded the ratios at 1 to 367, 1 to 546, and 15 to 367 days. The last ratio was taken
25
a
20 15 10
- GEDAYSH
25
50
5O 1OO 2OO 30O 4OO 5OO
Chart 43 The diameter of the largest cell bodies and of the nuclei from the ganglion vestibulare. table 115.
Cell bodies. -.-.-.-.-. Nuclei.
to facilitate a comparison with the data in table 118 which begin at 15 days.
Looking at the ratios of the cell bodies and of their nuclei from 1 to 546 days, it appears that the ganglion cells increase 1.2 in diameter, while their nuclei have only a very slight increase, and therefore the ratio is 1 : 1.0. This increase in the cell bodies is continuous from birth to old age, but after fifteen days is very slow. In the nucleus we see a slight increase at the earlier ages, after which the values are nearly constant. This means that after birth the size of the cell bodies and their nuclei does not increase so much as do those of the spiral ganglion cells, or, expressed in another way, the cells in the vestibular ganglion have developed earlier than those of the spiral ganglia and at birth have already attained nearly their full size.
On the comparison of the diameter of the cell bodies and their nuclei in the nerve cells of ihe ganglion vestibulare according to sex. For this purpose twelve age groups of albino rats were used. In seven cases we have two cochlea in each group in the same sex, in which the average value is recorded. In table 116 are entered the values for these diameters and at the foot of the table the data are analysed. They reveal no evidence of a significant difference in the diameters according to sex.
On the comparison of the diameters in the cell bodies and nuclei of the nerve cells in the ganglion ves ibulare according to side. For the present study fourteen age groups were employed. As indicated in table 117, the data in five instances are based on the average of two cochleas of the same side. Table 117 enables us to make the comparison of the diameters of the cell bodies and their nuclei on both sides, and the analysis of the data given at the bottom of the table shows that there is no difference in these characters according to side.
On the morphological changes in the cells of the vestibular ganglion. Figure 14 illustrates semi-diagrammatically the ganglion cells in the vestibular ganglion of the albino at birth, 20 and 367 days of age. These figures, as in the ganglion spirale, have been magnified 1000 times and the absolute values of the diameters are given in table 115.
As seen in figure 14, both the cell body and the nucleus are at birth already well developed and more precocious in their development than the cells in any of the other cerebrospinal ganglia thus far examined. The cytoplasm is relatively abundant and the Nissl bodies are present, though both of these characters become more marked later.
The nucleus is also large, the chromatin somewhat differentiated and the so-called 'Kernfaden' often occur. Generally speaking,
I Day
20 Days
14
366 Days
Fig. 14 Showing setrii-diagrammatically the size and the morphological changes in the ganglion cells in the ganglion vestibulare of the albino rat at the age of 1, 20 and 366 days. All cell figures have been magnified 1000 diameters.
GROWTH OF THE INNER EAR OF ALBINO RAT
161
therefore, the cells have the characteristics of the mature elements though they stain less deeply than in the adult. At twenty days of age the cell body is enlarged and fully mature. The Nissl
TABLE 116
Comparison of the diameters of the cells and their nuclei in the ganglion vestibidare
according to sex
AGE
BODY
WEIGHT
NUMBER OF
RATS
8EX
COMPUTED DIAMETERS
Cell body
Nucleus
days
grams
1
6
2
f
20.8
11.9
9
19.9
11.5
3
9
2
tf
21.7
11.8
8
2
9
23.8
12.2
6
11
2
tf
22.7
11.9
10
2
9
23.1
12.1
9
11
1
d*
23.8
12.5
9
1
9
23.8
12.1
12
15
1
cf
24.4
12.2
12
1
9
23.1
11.9
15
13
2
cf
24.3
12.2
13
2
9
23.4
11.9
20
30
1
cf
24.7
11.9
19
1
9
24.6
12.6
25
34
2
d"
24.4
11.9
34
2
9
24.4
12.4
50
43
2
cT
26.1
12.4
58
2
9
22.6
11.4
100
146
1
<?
26.3
12.8
103
1
9
23.4
12.6
150
194
2
rf 1
24.4
12.5
154
2
9
24.4
12.0
365
205
1
<f
24.2
11.7
170
1
9
24.6
12.1
Average for male
24.0
12.1
Average for female
23.4
12.1
Males larger
6
7
Females larger
3
5
Males and females equal
3
bodies are more differentiated and the nucleus is mature, though
it shows only a slight increase in size.
At 367 days the histological structures appear much as at twenty days, but the diameters of both the cell body and the nucleus have very slightly increased. This is in contrast to the change which occurs in the cells of the spiral ganglion.
162
ANATOMICAL AND PHYSIOLOGICAL STUDIES ON
In order to study the form of the cells of the ganglion vestibulare the measurements also were made on the cross-sections. Table
TABLE 117
Comparison of the diameters of the cells and their nuclei in the ganglion vestibulare according to side
AGE
BODY
WEIGHT
NUMBER
OF RATS
SIDE
COMPUTED DIAMETERS
Cell body
Nucleus
days
grams
1
4
1
R.
20.1
12.0
5
1
L.
22.0
12.5
3
9
2
R.
23.0
11.8
L.
22.6
12.3
6
10
1
R.
23.2
12.1
L.
23.5
12.0
9
11
1
R.
25.1
12.3
L.
23.8
12.5
12
15
1
R.
24.4
12.2
13
1
L.
25.1
12.5
15
13
2
R.
24.2
12.2
L.
23.6
11.9
20
30
1
R.
24.7
11.9
L.
23.5
11.4
25
34
2
R.
23.9
12.1
L.
24.9
12.2
50
50
2
R.
23.1
11.6
L.
25.6
12.3
100
101
1
R.
25.0
12.0
L.
24.8
11.7
150
199
1
R.
25.1
12.8
154
1
L.
25.4
12.5
263
140
1
R.
26.5
12.3
L.
25.1
12.4
368
179
1
R.
27.2
12.6
L.
26.2
13.0
546
255
2
R.
26.0
12.4
L.
24.6
12.0
Average right side
24.4
12.2
Average left side
24.3
12.2
Right larger
8
6
Left larger
6
8
118 (chart 44) shows the results. Looking at the ratios of 15 to 371 days, we see the same rate of increase in the cell bodies and the nuclei as that in the radial section; i.e., in the cell bodies 1 : 1.1 and in the nuclei 1 : 1.0. Comparing the diameters at each
GROWTH OF THE INNER EAR OF ALBINO RAT
163
TABLE 118
Diameters of the cell bodies and their nuclei in the ganglion vestibulare, on crosssection (chart 44)
DIAMETERS M
AOK
BOOT
WEIGHT
CELL BODY
NUCLEUS
Long
Short
Computed
Long
Short
Computed
days
grams
15
20
25.1
22.8
23.9
12.4
11.6
12.0
20
27
25.2
23.4
24.3
12.5
11.7
12.1
25
39
25.2
24.0
24.6
12.3
12.0
12.1
100
95
26.6
24.7
25.6
12.8
11.8
12.3
150
169
26.7
24.7
25.7
13.0
11.7
12.3
371
220
26.8
25.3
26.0
12.8
11.8
12.3
Ratio 15-371 days 1:1.1
1 :1.0
25
20
15
10
25
50
50 10O 20O 300 40O 5OO
Chart 44 The diameters of the cell bodies and of their nuclei from the ganglion vestibulare, after fifteen days (cross-section), table 118. Cell bodies. -.-.-.-.-. Nuclei.
164
ANATOMICAL AND PHYSIOLOGICAL STUDIES ON
age in both the radial and cross-sections, they are almost the same, with a slight tendency for the cells in the cross-section to give higher values, which suggests that the long axes of these cells tend to lie in the plane of the section.
On the nucleus-plasma relations of the ganglion cells in the ganlion vestibulare. In table 119 are entered the computed diameters of the cell bodies and their nuclei in the radial section, and in the last column the ratios of the volume of the nucleus to that of the cytoplasm obtained by the method previously given. As
TABLE 119
Nucleus-plasma ratios of the cells in the. ganglion vestibulare radial vertical section
COMPUTED DIAMETERS M
AGE
BODY WEIGHT
Cell body
Nucleus
Nucleus-plasma
ratios
days
1
grams
5
20.3
11.7
1 :4.2
3
9
22.9
12.0
- 5.9
6
11
23.0
11.9
- 6.2
9
10
23.9
12.0
- 6.9
12
13
23.9
12.1
- 6.7
15
13
23.9
12.0
- 6.9
20
27
24.1
11.9
- 7.3
25
34
24.4
12.1
- 7.2
50
50
24.5
12.0
- 7.5
100
112
24.7
12.3
- 7.1
150
174
24.4
12.2
- 7.0
260
138
24.6
12.0
- 7.6
367
184
25.5
12.3
- 7.9
546
255
25.3
12.2
- 7.9
seen, the ratio is at birth relatively large, 1 : 4.2, and this increases with age, in the earlier stages considerably, but in the later, less rapidly. In the oldest age group it is largest, 1: 7.9.
On the cross-section the nucleus-plasma ratio is also progressive and the increase is very regular (table 120). Comparing the ratios in the radial with those in the cross-sections, they are found to be nearly the same at fifteen twenty and twenty-five days, but at the later ages those in the cross-sections are somewhat larger than in the radial. It is difficult to determine whether the ratios on the cross-section are really larger or whether the
GROWTH OF THE INNER EAR OF ALBINO RAT
105
result depends on the fact that the number of the cells here measured is only one-fourth of that measured in the radial section, and hence fewer cells of smaller size were included. At any rate, these ganglion cells in both the radial and crosssections of the cochlea appear to grow at about the same rate. The statistical constants for these cells and their nuclei are given in tables 121 and 122.
Discussion
The nerve cells in the ganglion vestibulare are, as seen from the above description, already well developed at birth both in size and histological structure. After that time they grow con TABLE 120
Nucleus-plasma ratios of cells of the ganglion vestibulare, in cross-section
DIAMETERS COMPUTED M
BOOT
AGE
WEIGHT
Cell body
Nucleus
Nucleus-plasma
ratios
days
grams
15
20
23.9
12.0
1 :6.9
20
27
24.3
12.1
- 7.1
25
39
24. ti
12.1
- 7.4
100
95
25.6
12.3
- 8.0
150
169
25.7
12.3
- 8.1
371
220
26.0
12.3
- 8.4
tinuously but slowly so long as followed. The increase from 1 to 546 days in the ratios of the diameters is in the cell body 1: 1.3, in the nucleus 1: 1.1, and is therefore very small. In the cerebrospinal ganglion cells and in the cells of the cerebral cortex, studied in the albino rat, there is no case which shows such a small rate of increase between birth and maturity. The following table 123 shows the ratios of increase which have been found.
It is to be noted that for the cells of the seventh spinal ganglion and the spinal cord, the ratios were taken from 17 to 360 days. If we had the ratios from 1 to 360 days, they would be without question much larger.
There are a few measurements on the size of the ganglion cells in the vestibular ganglion of various animals in the liter
166
ANATOMICAL AND PHYSIOLOGICAL STUDIES ON
ature. Schwalbe ('87) and Alexander ('99) report measurements on these cells in several animals, but for the reasons already given when considering the diameters of the cells in the ganglion spirale, the values obtained by the authors are not repeated here.
TABLE 121
Giving the mean, standard deviation and coefficient of variability, with their respective probable errors, for the diameters of the cells in the ganglion vestibulare, in radial-vertical section
AGE
CELL
NUCLEUS
MEAN
STANDARD
DEVIATION
COEFFICIENT OF
VARIABILITY
days
1
Cell
20.1 0.16
1.46 0.11
7.3 0.55
Nucleus
11.7 0.11
0.99 0.07
8.5 0.64
3
Cell
22.6 0.14
1.33 0.10
5.9 0.44
Nucleus
11.9 0.07
0.63 0.05
5.3 0.40
6
Cell
22.8 0.13
1.23 0.09
5.4 0.41
Nucleus
11.9 0.05
0.43 0.03
3.6 0.27
9
Cell
23.6 0.16
1.48 0.11
6.3 0.48
Nucleus
12.0 0.0<9
0.82 0.06
6.8 0.52
12
Cell
23.6 0.14
1.28 0.10
5.4 0.41
Nucleus
12.0 0.06
. 59 . 04
4.9 0.37
15
Cell
23.6 0.13
1.21 0.09
5.1 0.39
Nucleus
12.1 0.06
0.60 0.05
5.0 0.38
20
Cell
23.9 0.16
1.54 0.11
6.5 0.49
Nucleus
11.9 0.10
0.90 0.07
7.6 0.55
25
Cell
24.2 0.16
1.48 0.11
6.1 0.46
Nucleus
12.1 0.08
0.74 0.06
6.1 0.46
50
Cell
24.1 0.30
2.80 0.21
11.6 0.88
Nucleus
11.8 0.09
0.86 0.06
7.3 0.55
100
Cell
24.3 0.20
1.86 0.14
7 . 7 . 58
Nucleus
12.2 0.09
0.86 0.06
7.0 0.53
150
Cell
24.1 0.18
1.70 0.13
7.1 0.53
Nucleus
12.2 0.09
0.83 0.06
6.8 0.52
260
Cell
24.3 0.26
2.45 0.18
10.1 0.76
Nucleus
11.9 0.07
0.67 0.05
5.6 0.42
367
Cell
25.2 0.22
2.07 0.16
8.2 0.62
Nucleus
12.3 0.09
0.88 0.07
7.2 0.54
546
Cell
25.0 0.19
1.80 0.14
7.2 0.54
Nucleus
12.1 0.09
0.81 0.06
6.7 0.50
On the differences between the growth of the cells in the ganglion spirale and ganglion vestibulare. The foregoing discussion has made plain that the vestibular ganglion cells grow not only in size, but also in histological structure very much before birth, while after birth they grow slowly though continuously. On the other hand, the spiral ganglion cells are relatively immature at
GROWTH OF THE INNER EAR OF ALBINO RAT
167
birth, but in the earlier stages after birth grow very rapidly, reach at twenty days their maximum size, and then diminish slowly. This great difference in the course of growth is probably related to the maturity of the functions of the animal.
TABLE 122
Giving the mean, standard deviation and coefficient of variability with their respective probable errors for the diameters of the cells in the ganglion vestibulare on cross-section
AGE
days
CELL
NUCLEUS
MEAN
STANDARD
DEVIATION
COEFFICIENT OF
VARIABILITY
15
Cell
23.8 0.21
1.00 0.15
4.2 0.58
Nucleus
12.0 0.12
0.55 0.08
4.6 0.69
20
Cell
23.9 0.20
0.92 0.14
3.9 0.58
Nucleus
12.1 0.06
0.30 0.05
2.5 0.37
25
Cell
24.4 0.20
0.94 0.14
3.9 0.58
Nucleus
12.1 0.03
0.16 0.02
1.3 0.20
100
Cell
25.4 0.32
1.51 0.23
5.9 0.90
Nucleus
12.3 0.15
0.72 0.11
5.9 0.88
150
Cell
25.6 0.20
0.94 0.14
3.7 0.55
Nucleus
12.4 0.09
0.42 0.06
3.4 0.51
371
Cell
25.9 0.41
1.91 0.29
7.4 1.11
Nucleus
12.3 0.06
0.26 0.04
2.1 0.32
TABLE 123 Ratios of diameters between the ages given.
CEREBRAL CORTEX
DONALDSON AND
(SUGITA, '18)
NAOABAKA. '18
CELL
GROUP
LAMINA
LAMINA
OA88ERIAN
SPIRAL
VESTIBULAR
7TH
EFFERENT
PYHA
GANO
GANGLION
GANGLION
GANGLION
SPINAL
SPINAL
MIDIS
LIONARIS
NITTONO
WADA
WADA
GANGLION
CORD
C20)
CELLS
Age
days
1-730
1-730
1-330
1-546
1-546
17-360
17-360
Cell
body
1 :1.6
1 : 1.6
1 : 1.69
1 : 1.6
1 :1.2
1 :1.3
1 :1.2
Nucleus
- 1.5
- 1.5
- 1.20
- 1.2
- 1.0
- 1.2
- 1.2
As a consequence, in the nucleus-plasma ratio there is also a large difference between the cells in the two ganglia. Table 124 shows this.
The ratio at birth in the ganglion vestibulare is large as compared with that in the ganglion spirale, but the increase in this ratio
168 ANATOMICAL AND PHYSIOLOGICAL STUDIES ON
at 546 days is relatively slight as compared with what takes place in the cells of the ganglion spirale. It appears, therefore, that the cells in the vestibular ganglion are at birth in a more mature condition.
As to the correlation between the development of the ganglion cells and the equilibrium function, we have noted that the albino rats, even just after birth, show some sense of equilibrium, though the movements are lacking in coordination. With advancing age the balance of the body is held much better and all the movements gradually become coordinated. The histological structure and the size of the cells at birth suggest that they are functional at that time, and the later increase in the volume and maturity of the cells is accompanied by a corresponding
TABLE 124
GANGLION VESTIBULARE
GANGLION
SPIRALE
Nucleus-plasma ratio at one day
Nucleus-plasma ratio at 546 days
1 :4.8
- 7.9
1 : 1.3
- 4.2
increase in the functional development. When the tactile sense is well developed and the eyes open equilibrium is almost perfected. It is a well-known fact that these two senses have very intimate relations to the maintenance of equilibrium. In this case, as we might expect, the early development of a function is accompanied by an early maturing of the neural mechanism on which it depends.
Conclusions (for the ganglion vestibulare)
1. The measurements were taken on the largest nerve cells of the ganglion vestibulare in the radial section of the cochlea, and the developmental changes during portnatal growth studied in fourteen age groups, comprising four ears in each group. Further, in six age groups the cell size was determined in crosssections. The results have been given n tables 115 and 118 and charts 43 and 44.
GROWTH OF THE INNER EAR OF ALBINO RAT 169
2. The computed diameter at birth is 20.3 [x for the cell body and 11.7 ^ for the nucleus, and at 546 days, 25.3 and 12.2 n, respectively. Therefore the cells at birth are comparatively large and increase in size very slowly, but the increase is continuous.
3. The increase in the ratio of the cell body is as 1 : 1.3, of the nucleus as 1 : 1.1. We have between the same age limits no such small rate of increase in any other cerebrospinal ganglion studied in the albino rat. This small ratio indicates that the cells in the vestibular ganglion are well developed at birth.
4. We find no appreciable difference in the diameters of the cell bodies or the nuclei according either to sex or side.
5. Morphologically, the cells at birth are well differentiated. The form of the cells is ovoid.
6. The nucleus-plasma ratios are large at birth and increase regularly with age.
7. Comparing the development of the function of equilibrium with the growth of the cells, we see that these are correlated.
Final summary
This study is concerned with the age changes in the organ of Corti and the associated structures. The changes in the largest nerve cells which constitute the spiral ganglion and the vestibular ganglion, respectively, have also been followed from birth to maturity. On pages 116 to 124 are given the summary and discussion of the observations on the growth of the tympanic wall of the ductus cochlearis.
The conclusions reached from the study of the largest nerve cells in the ganglion spirale appear on pages 143 to 145. On pages 155 and 156 are presented the results of the study on the correlation between the response to sound and to the conditions of the cochlea.
Finally, the observations on the growth of the largest cells in the ganglion vestibu'are are summarized on pages 168 and 169.
It is not necessary to again state in detail the conclusions reached in the various parts of this study.
At the same time, if we endeavor to obtain a very general picture of the events and changes thus described, this may be sketched as follows:
170 ANATOMICAL AND PHYSIOLOGICAL STUDIES ON
Within the membranous cochlea there occurs a wave of growth passing from the axis to the periphery as shown in figures 4 to 13. The crest or highest point of the tissue mass appears at birth near the axis, in the greater epithelial ridge, and then progressively shifts toward the periphery, so that at maturity it is in the region of the Hensen cells. With advancing age the hair cells come to lie more and more under the tectorial membrane and the pillar cells seem to shift toward the axis.
At from 9 to 12 days the tunnel of Corti appears and the rat can hear.
All of these changes occur first in the basal turn and progress toward the apex. The mature relations are established at about twenty days. There are thus two waves of change in the membranous cochlea, from the axis to the periphery and the other from the base to the apex. The rat can usually hear at twelve days of age or about three days before the eyes open.
The largest cells in the ganglion spirale are very immature at birth, reach their maximum at twenty days, and after that diminish in size, slightly but steadily. The rat hears, therefore, before these cells have reached their full size.
The largest cells in the vestibular ganglion are precocious and remarkably developed, even at birth. They cease their rapid growth at about fifteen days of age, but increase very slightly though steadily throughout life.
