CYCLIC CHANGES IN UTERUS AND OVARIES. 4! 



structures; afterwards they begin to reappear, from the eighth 

 day on to the end of the sexual cycle mitoses are absent in the 

 connective tissue. 



2. As long as the corpora lutea functionate, the presence of 

 mature follicles in the ovaries does not produce those changes in 

 the uterine mucosa which are characteristic of the period of 

 heat. 



3. During pregnancy the structure of the uterus is that of a 

 resting organ, in which epithelial as well as connective tissue 

 cells are small and the latter are without mitotic proliferation. 



4. In animals in which heat has been observed without copula- 

 tion taking place, the cyclic changes in the uterus are approxi- 

 mately the same as in animals in which copulation did take place, 

 in which however pregnancy had been prevented through an 

 early ligature of the fallopian tubes. The main difference in 

 these two series is caused through the very marked migration of 

 polynuclear leucocytes through the mucosa in cases in which 

 copulation took place. 



5. Ovulation is usually accompanied or directly followed by 

 certain changes in the uterine mucosa. These changes permit 

 us in many cases to decide whether or not in an animal in the 

 period of heat ovulation has or has not yet taken place. 



6. Extirpation of almost the whole uterus or thyroids does 

 not prevent the occurrence of heat in the operated animals. 



7. In animals which were prevented from copulating or in 

 which the fallopian tubes were ligated soon after copulation, the 

 period of heat occurs approximately every fifteen to nineteen 

 days. 



8. The proportion of ovarian follicles which are in the late 

 stages of connective tissue atresia to well preserved follicles and 

 follicles in the stage of granulosa degeneration shows two maxima, 

 one about six to seven days after ovulation and another at the time 

 preceding the next ovulation. Under certain conditions, how- 

 ever, the number of quite atretic follicles may be small at the 

 time of heat, namely in young guinea-pigs which are in heat for 

 the first time, and it may be relatively large at other periods of 

 the sexual cycle in old guinea-pigs. 



9. As we showed previously an early extirpation of the corpora 



