264 INTERNAL SECRETIONS 



most animals ovulation is preceded by the so-called "pro- 

 oestrum," which is the first stage of heat; this is further 

 evidence that there are no corpora lutea at the beginning of 

 heat. In those cases where an ovulation takes place sometimes 

 only after coition (see above), heat cannot be caused by a real 

 corpus luteum. Marshall and Runciman performed experi- 

 ments on the question of time relations between ovarian changes 

 and heat. They concluded tentatively that in the dog the 

 commencement of heat does not necessarily depend upon ripe 

 Graafian follicles or corpora lutea. 



In subsequent experiments by Marshall and Wood (1923), 

 however, it is shown that the occurrence of heat is normally 

 correlated with the presence of follicles in what is called the 

 " pre-inseminal stage." Marshall and Wood destroyed in 

 dogs the ripe Graafian follicles by cauterisation a short time 

 before a heat period was due; the period was missed; on the 

 contrary, heat was not postponed, or only sHghtly so, if the 

 follicles were cut into without being destroyed. The results 

 were the same as in the former experiments of Marshall and 

 Runciman, the Graafian follicles having been only pricked and 

 ruptured. 



According to Aschner, one must assume that the follicle, and 

 especially the ovum itself, produces the internal secretion of 

 the ovary. As to the ovum, this conception is absolutely 

 unfounded and unacceptable; only a few of those who are 

 consistently antagonistic to the conception of the endocrine 

 function of the interstitial cells, have adopted this standpoint. 

 There is, indeed, no evidence whatever that the ovum itself acts 

 in the mammal as a gland with an internal secretion. In one of 

 our experiments already mentioned only a small percentage of 

 the normal quantity of ova was present in the hypertrophied 

 ovarian fragments, and nevertheless this animal had a uterus 

 better developed than that of a control animal of the same litter. 

 The ripening of the ovum seems to be an essential influence, 

 since the transformation of hitherto inactive cells into active 

 endocrine cells evidently depends on some process going on in 

 the ovum and connected with its ripening. The view that the 

 follicles in general can cause menstrual changes by an internal 

 secretion is not contrary to the assumption that the corpus 

 luteum has this function. From what we have learnt in the 

 preceding paragraphs of this section it seems clear enough that 



