164 



Scientific Proceedings (76). 



period (December and first half of February) the ovaries of the 

 ferret are small and differ from the ovaries in the period of sexual 

 activity especially through the diminution in the number of good 

 follicles. While the ovaries as a whole are smaller, the interstitial 

 gland is well preserved during the winter months. 



91 ("55) 



The cyclic changes in the mammary gland of the guinea pig- 

 By Cora Hesselberg and Leo Loeb. 



[From the Department of Comparative Pathology, Washington 

 University, St. Louis, Mo.] 



Our interest in the character of the cyclic changes of the 

 mammary gland and in their mechanism was twofold. (1) In 

 former investigations Loeb has shown that an early extirpation of 

 the ovaries reduces to a very marked extent the incidence of 

 cancer of the breast in mice. It was therefore of interest to in- 

 quire more closely into the relations between ovaries and mammary 

 gland, and (2) we wished to determine whether there exists a paral- 

 lelism between the cyclic changes in the mammary gland on the 

 one hand and in the ovaries and uterus on the other hand. One of 

 us had formerly shown that in the cyclic changes of ovaries and 

 uterus we could distinguish two phases: the first, comprising ovu- 

 lation and the heat changes in the uterus, depends upon the ab- 

 sence of the corpus luteum. These are prevented by a substance 

 secreted by the lutein cells. This phase is, however, dependent 

 upon another constituent of the ovaries. The second phase, 

 comprising the further cyclic changes in the uterus as well as the 

 production of decidua and deciduomata, requires a substance 

 secreted by the corpus luteum. Do corresponding phases exist 

 in the case of the mammary gland? 



Relatively little is known concerning the cyclic changes in the 

 mammary gland. Bouin and Ancel, as well as Frank and Unger, 

 have shown that in the rabbit, even in the absence of pregnancy, 

 but in the presence of corpora lutea, proliferation takes place in 

 the mammary gland. Proliferation also occurs regularly during 

 pregnancy. Frank and Unger have furthermore demonstrated 



