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Mitotic activity in the anterior hypophysis of female rats.

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MITOTIC ACTIVITY I N THE ANTERIOR
HTPOPHYSIS O F FEMALE R,ATS
THOMAS E. HUST
IkpUit?&?nt of Anatomy, university of Alabamu
INTRODUCTIOX
Mitotic activity in the pars glandularis of the hypophysis
of sexually mature rats is usually considered to occur infrequently. Wolfe ('35a), for instance, reports no more than
a n average of three mitoses per section in the rat hypophysis
and others have reported even fewer or none in normal
animals. Only in experimental animals have considerable
numbers been found. Wolfe ( '35 b) and Halpern and D'Amour
('36) described numerous mitotic figures in the pituitary of
rats after administration of oestrin and TYolfe ('35c) reported an increase after injections of pregnancy urine.
Ponierat ( '41) has found considerable mitotic activity in immature and young mature, unoperated and castrated male
rats after injections of colchicine.
It is surprising that cell divisions have not been found also
in the normal animal since the hypophysis of rats (Hatai,
'13) continues to increase considerably in size and weight
aftcr sexual maturity is reached. Furthermore, according to
Rirkman ('37), cells are lost in the guinea pig hypophysis
through degeneration or through the holocrine type of secretion. A priori, one can say that mitoses should take place t o
compeiisate for the cells lost as well as to account for growth
of the gland; therefore failure to observe mitoses may mean
that they were not looked for at the right time rather than
that they do riot occur at all. It is obvious that there is not
Aided by a grant from the TJniversity of Alabarnrt Research Fiind.
263
T H E ANA'COMIC'AC HRCOltn VOL. 8 2 . XI.
M A R C H . 1942
264
T H O M A S E. H U N T
a sigiiificunt, continuous mitotic activity but tlie possibility
remains that cells may divide during a certain period of the
estrous cycle. Tlie fact that estrogens may stimulate mitosis
suggests that cell divisions occur at a time when estrogens
are normally at a high level. Wolfe ('35 a), in fact, does
state that there are more mitoses in the rat hypophysis during
estrus than at other times but the nuniber that he reports
is not great.
There have been other attempts t o correlate mitotic activity
in various organs with the estrous cycle. Chouke, Friedman
and Loeb ( '35) reported that the maximum number of mitoses
in the thyroid of the guinea pig was found in the lutein phase
or approximately tlie fifth day of the cycle. Chouke, however,
more recently ('41) has stated that upon reexamining the
material he found that there is iiot a statistically significant
difference in mitotic activity at different periods of the cycle.
In the adrenal cortex of the rat I have found ('40) that
niitoses occur more frequently at diestrus than at other phases.
Thc work reported here shows that mitoses do occur in
significant numbers in the hypophysis and that there is a
cyclic mit,otic activity that map be correlated with the estrous
cycle.
~\TATRRIATIANT, METHODS
Tlic rats used were from the colony of Dr. C. 31. Goss w-hich
was started through the generosity of Dr. P. E. Smith and
included black, gray, hooded and albino types. The color did
not seem to have any significant bearing on tlie number of
mitoses found. The animals were fed on a dict of Purinachow supplemented with lettuce and milk. Food was available
constantly except f o r one group in which food was withheld
for 24 hours.
The animals were free from Bartonella niuris infection,
which may cause an increased mitotic activity in the reticuloendothelial system. This mas shown by the fact that splenectomy had no effect on the survival of a series of six j-oung
rats selected at random from differcnt cages of the colony.
MITOTIC ACTIVITY IX T H E H Y P O P H Y S I S
365
The stage of the estrous cycle in the mature animals was
ascertained by making vaginal smears daily for 2 or 3 weeks.
The leIigtli and character of the individual cycles was thus
determined approximately. Any animal not showing regular
cycles was discarded. I n the latter part of the series several
successive smears were made a t intervals of 2 or 3 hours
before killing an animal in order to determine more exactly
the stage of the cycle.
The majority of animals (exceptions noted in tables 2 and
3) were killed between 11 and 1 2 A.M. This was done since
many reports have stressed the variability of mitotic activity
at different periods of the day.
Animals were killed by severing the cervical spinal cord
with bone forceps. The brain was quickly removed from the
base of the’skull and the latter with the hypophysis in situ
was dropped immediately into fixing fluid. After fixation for
1 2 to 24 hours the gland was dissected away from the skull.
The fixative used was Allen’s B-15 fluid which was found to
be much superior to Bouin’s and other fixatives for studying
mitosis. The glands were cut serially in the coronal plane
at 3 micra and mounted at representative intervals. I n the
older glmcls every twenty-fifth section was taken, in the
younger ones every twelfth section. Every section was
mounted from glands less than 39 days old. The sections were
stained for the most part with iron hematoxylin followed by
acid fuchsin and anilin blue (Masson’s method).
The number of mitoses per square millimeter of section was
determined since the expression of mitotic activity by tlic
number found per section does not allow for very accurate
comparisons. Sections taken at different levels of a gland
may vary from 2 to 6 sq.mm. and unless the different glands
are cut in exactly the same plane another variable is encountered. The area of a section was calculated after measuring with a planimeter the area of the section projected at a
magnification of 50 diameters. I n making the counts a 4 mni.
~
were used. The latter had an ocular
objective and a 7 . 5 ocular
disc marked with twenty-five 5 mm. squares that covered
266
THOMAS E. H U N T
I/lo sqmni. of the section. By running the section from one
square t o the liest the entire section was examined without
duplicating fields. The stage of mitosis and, insofar as possible, the type of cell was noted in each case.
RESULTS
The mitotic activity was determined in two main groups
of rats, the immature and the mature.
Mitotic activity irt the hypophysis of immature female rats
In this series of nineteen animals (table 1) ranging from
1 to 50 days of age there is a decline from eighty-five to
ninety-nine mitoses per square millimeter of section on the
first day to one to six per square millimeter on.the fiftieth.
There is some variability between individuals that are litter
mates as in the case of 182a, b and c but the difference is not
great. There is likewise some difference in the count from
glands from different litters of the same age as between 110.
104b (eighty-five mitoses per square millimeter) and no. 186
(ninety-nine mitoses per square millimeter). These differences, however, are minor ones and the principal point is that
there is a gradual decline in the mitotic activity as the animals
become older which continues until sexual maturity is reached.
A similar decline in mitotic activity was noted by Pomerat
('41) in young male rats which had been injected with
colchicine.
Mitotic activity in the hypophysis of mature female rats
I n those animals which are mature there is a clear cut
difference in the mitotic activity at different stages of the
estrous cycle. Animals in proestrus and diestrus show relatively few mitotic figures, but during the latter half of estrus
(table 2, LE), there are surprisingly large numbers of dividing cells. In one specimen as many as seventy-two mitoses
per square millimeter of section were counted (no. 76, table
2) - a total of 357 in R T,-nim. iirea, 3 micra in thickness.
267
MITOTIC ACTIVITY 1X THE HYPOPHYSIS
EXPLANATION O F TABLES
’
Under the coluinn designated, ‘ ‘ Mitoses per square millimeter’ the quotient is
given of the total iinniber of mitoses counted h oiic gland divided by the total
area of sectioiis examined.
The “Mitoses per sertion” is used t o allow comparison with results presented
i n t h a t ii-vay by other workers. In making such comparisons, how-eyer, it should
be remembered t h a t others may have cut sections a t a different thickness and in
different planes.
The abbreviations f o r color of the animal are as follows: G - gray, B -black,
W -white, GH - gray-hooded, BH - black-hooded.
Under “Hour killed,’’ thc time given is hours a f t e r 1 2 midnight. Thus, hour 15
is used t o designatc 3 P.N. All immature animals werc killed between 11 mid
1 2 A.X.
The abbreviations f o r the stages of the cycle a r e as follows: EE -early estrus,
LE - late estrus, E - estrus (exact stage unknown b u t definitely estrns),
M - metestrus, D - diestrus, P - proestrus.
TABLE 1
Jlitotic activity in immature f e m a l e rats.
I
NO. OF
RAT
AGE 1N
EXAMINED
DAYS
MITOSES
COUNTED
JIITOSES
PER SQUARE
MILLIYETER
SECTIONS
EXAMINED
YILLIIIETERS
I
186
104:l
104b
178a
l78b
182a
182b
18%
174%
1741)
l7Oa
1701)
17OC
165%
I65b
77
12.5
90
89
19
4.50
2.43
1.69
6.93
3.23
3.81
4.81
5.33
6.00
5.09
3.68
3.31
7.35
33.59
12.46
6.72
10.89
13.59
6.01
1
1
1
7
7
10
10
10
14
14
16
16
16
20
20
24
39
50
51
447
212
144
550
242
225
242
269
232
169
163
92
199
244
186
30
I50
91
8
99.3
87.2
85.2
79.4
74.9
59.1
50.5
50.3
38.7
33.2
28.7
27.8
27.1
18.0
15.0
4.5
11.6
6.7
1.3
I
I
123
3.895
1
11
13
10
10
MITOSES
PER
SECTION
41
16
14
55
27
25
2T
30
17
01
20
10
25
31
31
5
30
I1
9
9
9
9
14
8
8
8
8
8
6
6
5
8
7
1
-
268
THOMAS E. HUNT
TABLE 2
Mitotic QCtiVity in mature female rats.
-
~
-
8::
*
K
M
f.
0
E
-
~
141
83
84
191
1.93
194
86
69
74
190
203
198
199
202
66
119
121
68
s
0
$4
i
17.03
21.7@
9.01
11.79
6.85
16.71
5.99
21.74
32.74
13.85
12.23
17.10
18.39
9.83
30.77
10.91
12.77
34.50
53
62
69
73
76
87
90
92
97
101
103
105
105
106
126
135
135
185
171
262
103
78
16
93
45
197
463
37
72
307
91
57
175
87
152
59
10.0
12.1
11.4
6.6
2.3
5.6
7.5
9.1
14.1
2.7
5.9
18.0
5.0
5.8
5.7
8.0
11.9
1.7
4
8
2
4
4
4
2
11
8
4
4
4
4
3
-
4
5
8
43
33
51
20
4
23
28
18
52
9
18
77
33
19
25
22
30
7
G
G
w
W
G
G
B
w
W
w
B
c*
:H
w
w
G
G
c:
-
142
Ii5
175
160
158
180
180
165
li5
160
214
195
195
1ii
180
153
159
224
13
12
12
6
20
20
11
12
11
5
12
18
19
11
12
11
11
12
10
12
4
4
12
16
9
9
16
EE
EE
EE
EE
EX
EE
EE
EE
El3
EE
EE
EE
EE
EE
EE
EE
BE
El7
~
18
126
139
142
140
116
81
105
213
76
214
75
196
107
$04
2,465
8.34
15.90
17.84
12.28
14.73
19.90
23.66
19.06
24.76
15.59
20.05
13.51
30.23
431
864
837
835
967
782
1,068
565
1,777
524
687
149
81 7
45
52
52
53
62
63
80
86
87
92
101
104
111
90
J I .7
54.3
46.9
68.0
65.7
39.3
45.1
29.6
71.8
33.6
34.3
11.0
27.(J
6
4
4
4
6
4
5
4
6
4
7
3
8
72
!16
!09
!09
61
96
114
.41
196
31
98
50
02
cr
126
138
149
148
135
165
15.5
198
160
G
170
W
G
180
189
LV
1i5
G
w
G
G
w
G
R
G
12
12
12
12
12
11
11
15
12
1.5
12
9
12
~
~
13
~
2.16
10.303
65
-
-
18
24
24
30
30
LE
LE
LE
JAE
LE
LE
LE
IX
TIE
LF:
LE
22
LE
TJF,
TABLE 3
*
Mitotic activity in mature female rats.
__
~
z$
I
C
$
ii $s
“;Bwa
3aEx
O P
B O
ii”
~
55
40
54
61
56
64
62
63
60
57
109
131
194
213
215
241
331
339
342
560
32.41
30.89
42.00
39.82
44.66
11.61
22.08
35.27
32.54
31.12
138
304
112
127
169
29
37
52
46
21
-
8c:
2,.
c
:as,
3;a
B
$3,
0
__
4.3
9.8
2.7
3.2
3.8
2.5
1.7
6
7
6
8
6
3
3
6
8
6
1.5
1.4
.7
P5
r’
X
-
185
182
235
255
220
225
245
220
270
208
11
12
11
12
11
12
18
12
11
11
187.
166
212
180
180
12
12
9
12
17
130
160
190
205
170
21 9
180
190
215
204
212
215
225
218
12
12
19
11
12
11
11
12
12
11
12
11
12
12
D
D
D
D
D
D
D
R
1Go
R
155
178
216
17-1.
170
210
12
12
12
12
12
12
12
P
P
P
P
P
P
P
G
B
W
G
BH
G
W
23
43
18
16
28
10
12
9
6
3
E
w
B
B
E
E
E
I3
E
E
E
E
E
E
~
322
10
195
192
212
45
48
94
94
114
151
156
,035
59
12.25
9.21
16.96
24.90
19.11
46
3.8
144 15.6
3.0
50
111 4.5
129
6.8
82
480
3
4
4
6
5
G
15
w
36
12
18
26
W
G
G
22
24
40
M
M
M
M
Ikf
~
5
82
87
88
99
85
215
39
41
46
44
47
50
53
43
66
68
68
93
96
114
131
131
202
206
206
223
222
223
13
16
28
2
19
10
4
2
0
0
0
2
3
0
204
14
163
80
!62
161
65
67
52
17.87
10.21
14.13
15.45
18.75
22.14
10.64
10.62
8.22
15.04
12.86
18.40
17.37
12.17
61
63
81
94
126
126
219
31
172
24
13
7
14
19
4
4
.1
4
1.0
.5
.4
.2
.2
5
4
2
2
2
4
2
4
6
0
4
0
0
0
.1
1.8
7.2
1.1
.6
.4
.8
.3
273
163
~
1.6
4.0
7.0
.5
4.0
2.5
2.0
1.0
0
0
0
.5
B
R
R
B
B
B
w
G
G
W
w
.5
R
0
0
cr
n
n
D
n
D
D
D
55
~
c
8
.7
1.6
2.0
99
17.49
33.96
21.10
22.21
17.94
18.70
41.51
~
22
7
6
6
5
5
5
7
41
-
4.4
30.0
4.0
2.6
1.4
2.8
3.7
cr
G
w
W
G
269
-
2'70
THOMAS E. HUNT
Although this was the highest count there are enough other
instances approaching it to indicate that it is not exceptional.
During proestrus and diestrus (table 3) the number of
cell divisions is uniformly low. The only exception is rat
no. 80 which has seven and two-tenths mitoses per square
millimeter. This animal had become sexually mature a few
days previously and it is possible that the larger number of
mitoses is an expression of the factors responsible for mitotic
activity before maturity. I n all other animals the number
of mitoses counted is not greater than two per square millimeter and is usually less.
After it was ascertained that considerable mitotic activit;v
occurred during the latter half of estrus, the attempt was
made to determine more accurately when it began and when
it ceased. I n the cases listed (table 2, LE) it may be assumed
that some of them have reached or a t least approached the
maximum activity. I n about half the cases the beginning of
estrus was known to liave occurred 18 to 30 hours previously.
In the others the time when cornified cells first appeared in
the smears is not known exactly but it is certain that the
animals were killed late in estrus. The smears in such cases
are composed of typical cheesy masses of cornified cells and
the uterus is 110 longer swollen.
The exact time in hours after the onset of estrus when
mitotic activity begins cannot be stated due to the individual
variations in the length of the cycles. This is illustrated by
animals nos. 198 and 199 (table 2, EE) which have eighteen
and five mitoses per square millimeter respectively. Both of
these animals were killed approximately 9 hours after cornified cells were first found in the vaginal smear. They were
litter mates and had the same weight but no. 198 had a cycle
of 4 days and 110. 199 had a cycle of 5 days. Otlicr similar
cases lead me to believe that rnitotic activity may appear
sooner in animals with short cycles. I n animal no. 194 which
was killed 4 hours after cornified cells were first found in the
smear there arc five and six-tenths mitoses per square millimeter. This is distinctly above the average for proestrus
MITOTIC ACTIVITY I N TIIE HYPOPIIPSIS
271
and diestrus and it may be assumed that mitotic activitj- niay
appear as early as this in some animals that run short cycles.
Mitotic activity diminishes and practically ceases during
metestrus (table 3). This is shown by the considerably decreased activity during this phase as compared with the latter
part of estrus and the essential lack of mitoses during diestrus.
Metestrus, which is characterized by the appearance of leucocytes among the cornified cells in smears, was found to occur
from 22 hours (no. 195) to 40 hours (no. 212) after the beginning of estrus. Long and Evans ('22) found the range of
time t o be 12 to 81 hours with the average length 27 hours.
While it is not possible to say with certainty, it seems likely
that mitotic activity continues over a period of 18 to 30 hours,
the difference depending on the length of estrus. It also
seems probable that in cases where there is a long period
of estrus the maximum mitotic rate is not as great as in those
cases where there is a short period. If this is true, the total
number of cell divisions occurring in a single cycle might be
the same in two cases that had markedly different mitotic
rates.
The age of the animal is another cause of variation in the
mitotic activity. I n general it has been found that the older
the animal the less frequent are mitoses. A sufficient number
of glands have been examined t o show that this is true. I t is
probable, however, that the maximum activity has not been
found in animals more than 111 days old. The older animals
were for the most part the first to be examined and not as
great care was used in determining the exact stage of the
cycle as later in the series. It is only known that they were
in some stage of estrus (table 3, E). The greatest mitotic
activity found in these older animals is in general less than
the least activity found in the group under 111 days of age.
The number of hours after ingestion of food map be a
factor in determining the mitotic rate in the hypophysis as
Rlumenthal ('40) found in the thyroid and adrenal gland of
the guinea pig. It is certainly not the primary factor, however. Rats nos. 119 and 121 (table 2, EE) were killed 24 hours
2i2
THOMAS E. H U N T
after food had been removed from the cage and the mitotic
activity is essentially the same as in comparable animals that
had food available a few hours before killing. Rats nos. 4<3
and 48 were killed 6 and 24 hours respectively after feeding.
The one without food for 24 hours has a somewhat greater
number of mitoses, to be sure, but the discrepancy can be
attributed more readily to other factors. Furthermore, it is
contrary to Blumenthal’s results which indicate that the
greatest activity is between the fourth and the twelfth hour
after feeding.
The time of day at which the animal is killed is likewise
not the primary factor that determines mitotic activity since
practically all glands were obtained between 11 and 12 A.M.
Animals killed at other times have about the same number
of mitoses provided the stage of estrus and age are the same.
The cell in which mitosis occurs in the mature animals is
usually the chromophobe. I n glands where mitochondria and
granules can be identified satisfactorily it is found that
only 5 to 10% of the mitoses occur in the granular acidophiles.
Of all the mitoses counted in the series none was identifled
with certainty in a basophile. The number of dividing acidophiles is usually greater in the younger mature animals than
in the older ones and in the ininiature animals it is sometimes
considerably greater. I n one case (no. 90,50 days of age when
sacrificed) there are as many as 50% of the dividing cells
that are acidophiles. I n some cases only a few fuchsinophilic
granules are present in the dividing cells. Whether such cells
represent a transformation from chromophobe to chromopliile
or vice versa could not be ascertained.
DISCUSSION
It is difficult to explain why mitoses in large numbers have
not been reported previously in a n organ studied as intensively as the rat hypopliysis. There are several possible
explanations. I n the first place, few studies have been made
that have been correlated with the estrous cycle. An esception
MITOTIC ACTIVITY I S THE HYPOPHYSIS
273
is the work of Wolfe ('35 a) who looked for mitoses in a total
of ninety-seven glands from mature rats. Of these, twenty
glands were from animals in estrus but it is not stated how
many of these were taken late in estrus nor is the age of the
animal given. While the average number of mitoses that he
observed at this phase is only three mitoses per section, this
number is higher than that found at other times. Other
investigators have studied the hypophysis from a cytological
point of view with or without regard to the phase of the cycle.
Usually the fixatives used in such cases were not adapted to
the study of mitotic activity.
It is not surprising that mitoses have not been generally
observed in animals that have a longer sex cycle than the rat.
The period during which mitotic activity occurs in these longer
cycles may be so protracted that only a few mitotic figures
would be found at any one time.
The question arises as to the primary factor responsible for
stiiiiulating mitoses in the hypophysis. Light, time of feeding
and time of day, which are usually mentioned in connection
with mitotic activity, can not be considered to be of primary
importance although they may be secondary factors. The
close correlation of mitotic activity in the hypophysis and the
changes in the ovary points to a direct or indirect relationship
between the two. Further, since mitotic activity is greatest
when the follicles are large or when ovulation has recently
occurred, it seems probable that an estrogen may be involved. The fact that administration of an estrogen (TTTolfe,
'35b; Halpern and D'Amour, '36) results in an increased
mitotic activity in the chromophobes of the hypophysis substantiates such a view but the dosage given to produce this
effect is greatly in excess of the physiological amounts during
estrus.
Whatever the stimulus may be that causes mitotic activity
in the hypophysis, it does not cause such activity simultaneously in any other organ so far as known. I have found that
the number of mitoses in the intestine does not vary signi-
274
THOMAS R. HUNT
ficantly during different phases of the cycle. I n the adrenal
cortex the greatest mitotic activity occurs during diestrus
(Hunt, '40). I n the reproductive tract mitotic activity in the
uterus and vagina occurs earlier in the cycle (Long and Evans,
'22) than it does in the Bypophysis. The stimulus thus appears to act specifically on the hypophysis.
It is probable that the high mitotic activity in the hypophpsis
provicles new cells to replace those that have degenerated.
The activity observed in diestrus and proestrus, since it is
coniparable t o that found in glands shortly before maturity,
is sufficient to account for the normal growth of the gland.
This difference in the observed mitotic activity in late estrus
and that required for growth of the gland necessitates the
assumption that newly forming cells will need additional
space that can be acquired only by a loss of a comparable
volume of degenerated cells. Degeneration of cells has been
obserred by Kirkman ('37) and otliers but it seems likely
that the process is even more extensive than that so far
described.
There is also the possibility that the greatly increased
mitotic activity observed in the latter part of estrus may be
correlated with the shift in cell proportions that occurs during
the estrous cycle. During estrus the percentage of granular
basophiles drops considerably in the rat, dog and sow (Wolfe
and co-workers) and in the guinea pig (Kirkman). The reappearance of these cells has been explained by their reversion
to chromophobes which again become basophiles. Severinghaus ( '37) has shown by cytological studies that such a transition may take place and if mitoses were as rare in the
lij-popliysis as is generally believed such an explanation would
be almost necessary. With the observation of large numbers
of mitoses, however, a second explanation is equally tenable,
namely, that the basophiles instead of reverting to chromophobes disappear by degeneration and are replaced by dividing chromophobes which in turn differentiate into ti new set
of ba sophiles.
MITOTIC ACTIVITY IN THE HYPOPHYSIS
275
SUMMARY AND CONCLUSIOXS
1. Mitotic activity in the hypophysis of immature female
rats declines from eighty-five to ninety-nine mitoses per
square millimeter of section on the first day to one to six
mitoses on the fiftieth.
2. I n mature female rats mitotic activity varies during the
estrous cycle as follows: ( a ) Mitotic activity begins and
increases during tlie first 12- to 16-hour period of estrus;
(b) The greatest number of mitotic figures is found 18 to 30
hours after the onset of estrus (as many as seventy-two
mitoses per square millimctcr in a section 3 micra in thickness). (c) Activity declines and practically ceases during
metestrus. (d) During diestrus and proestrus mitotic activity
is at a low level (usually less than two mitoses per square
millimeter of section).
3. There are indications that mitotic activity in sexually
mature rats declines as the animals become older.
4. The majority of mitoses occur in the chromophobes. Only
5 to 10% occur in thc acidophiles. None were found in
basophiles.
5. It is concluded that tlie mitotic activity in sexually mature
rats is greater than that necessary to account for the growth
of the gland and that it serves to compensate for cells lost
by degeneration.
LITERATURE CITED
RTXMENTHAL,HERMANT. 1940 The influence of time of feeding on the
periodicity in activity in thyroid and adrenal gland of normal male
guinea pigs. Endoerin., vol. 27, pp. 481-485.
C'IIOUKE,
I<. 8. 1941 Relationship of the proliferative activity of the thyroid
gland to the oestrons eyelo in the gninea pig. Anat. Ree., vol. 79
(suppl.), p. 14.
C'IIOUKE,
JTALPERN,
s., H I L D A F R I E D M a N A N D LEO LOER 1935 Proliferative activity
of tho thyroid gland of the female guinea pig during tlie sexual cycle.
Anat. Rcr., rol. 63, pp. 131-137.
I<.
5. R.,
AHD F. E. D'AMOUB 1936 Studies on the gonad-hypophyseal
complex in cstrin-injected rats. Am. a. Phpsiol., rol. 115, pp. 229-238.
276
T H O M A S E. H U X T
HATAI,SITINKISHI
1913 On the weights of the abdominal and the thoracic
viscera, the sex glands, ductless glands and the eyeballs of the albino
rat (Mus norregicus albinus) according t o body weight. Am. J. Anat.,
TO]. 15, pp. 87-119.
HEST, THOMASE. 1940 Mitotic activity of the adrenal gland of rats in
different phases of the sexual cycle. Anat. Rcc., vol. 78 (suppl.), p. 152.
KIRKIT
.ZN, HADLEY1937 A cytological study of the anterior hypophysis of the
guinea pig and a statistical an:~Iysis of i t s cell typrs. Am. .T. Anat.,
rol. 61, pp. 233-287.
LONG,JOSEPHA., BND HERBERT
If. EVANS 1922 The oestrous cycle in the rat
and its sssociatcd phenomena. Memoirs Unir. of Cal., vol. 6, pp.
1-148.
PoMcRAI,,
R. 1941 Mitotic activity in the pituitary of the white rat
following castration. L4m.J. Anat., vol. 69, pp. 89-121.
GERARD
SmmtIxGFr4cs, A. E. 1937 Ccllular chaiiges in the anterior hypophpsis with
special reference t o its secretory artirities. Physiol. Rev., vol. 17,
pp. 556-588.
WOLFE,J. M. 1935 a The normal level of the various cell types in the anterior
pituitaries of mature and immature rats and further observations on
cyclic histologic variations. Anat. Rrc., vol. 61, pp. 321-330.
1935 b Reaction of anterior pituitaries of mature female rats to
injections of large amounts of oestrin. Proc. Soe. Exp. Bid. and Med.,
vol. 30, pp. 1192-1195.
1935 c Morphologic reaction of the anterior pituitaries of mature
female rats to prolonged injectinus of pregnancy urine extracts. Anat.
Rec., ml. 63, pp. 1-11.
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