INTERNAL SECRETION OF CORPUS LUTEUM 199 



does not interfere with the occurrence of cestrus, and pregnancy 

 changes are not usually produced. In a few exceptional animals 

 (508), however, hypertrophy of the mouse uterus is produced by 

 X-irradiation, and is correlated with the occurrence in the 

 sterilized ovary of what Lipschiitz and others would call 

 interstitial tissue, but which w^as considered (84; to have a 

 greater resemblance to luteal tissue. 



As regards the stimulation of the mammary glands by 

 interstitial tissue, it is possible to quote the well-known feminiza- 

 tion of the male guinea-pig by an ovarian graft. No corpora 

 lutea or normal follicles are found in the graft, so that the femini- 

 zation is usually attributed to the large amount of interstitial 

 tissue produced by the graft (see p. 78). Since complete 

 development of the mammary glands is found in such feminized 

 males, the interstitial cells would seem to be capable of perform- 

 ing this function of the corpus luteum. This explanation of 

 hyperfeminization of the male is more probable than the 

 hypothesis that it depends on the production of cestrin by the 

 graft. 



x\ccording to Biedl (65) the human corpus luteum undergoes 

 degeneration at the end of the first half of pregnancy, and its 

 functions are then taken over by the interstitial tissue which is 

 increased during pregnancy by follicular atresia. 



On the other hand, interstitial tissue present before puberty 

 clearly performs none of the functions of the corpus luteum. In 

 many animals the interstitial tissue is said to be most abundant 

 before puberty — i.e. when none of the characteristic luteal 

 effects have yet appeared. In the rabbit, the changes in the 

 uterus and mammary glands characteristic of luteal activity do 

 not appear before the first ovulation, although the pre-pubertal 

 ovary is full of interstitial tissue. 



The whole problem is complicated by the lack of any agreed 

 definition of interstitial tissue and by the uncertain behaviour 

 of atretic folHcles. It seems clear that the granulosa cells of 

 atretic follicles in grafted ovaries produce all gradations of luteal 

 and interstitial cells (Steinach, 591), and until it is ascertained 

 whether an absolute difference exists between luteal and in- 

 terstitial cells further discussion can be of little value. 



