ORGANS OF INTERNAL SECRETION 335 



fact that ovulation in most Mammals does not occur until oestrus, 

 or, at any rate, until the end of the prooestrum (see p. 135), 

 and consequently corpora lutea are not present in the ovaries 

 (for the corpora lutea dating from one oestrus do not always 

 persist until the next oestrus, which may be many months after- 

 wards). Heape's observations l on the absence of corpora 

 lutea in menstruating monkeys may be again cited in this con- 

 nection. Moreover, Ries 2 has reported a case of a woman 

 with whom menstruation occurred normally after an operation in 

 which an oozing corpus luteum, which was a source of haemorrhage 

 in the peritoneal cavity, had been peeled out. It should be 

 mentioned that Fraenkel's views on menstruation are part of a 

 general theory which is discussed more fully below (p. 338). 



Seeing that the corpus luteum is not responsible for inducing 

 menstruation, it becomes necessary to conclude that either the 

 follicular epithelial cells or the interstitial cells of the ovarian 

 stroma (or both of these) are concerned in bringing about the 

 process (see p. 124). 



It has already been shown that the breeding season, and 

 consequently the recurrence of the oestrous cycle, are controlled 

 to a great extent by the general environmental conditions, 

 since these affect the physical state of the body (Chapters I. 

 and II.). This is particularly well seen in certain of the domestic 

 animals, in which " heat " may be caused to recur more fre- 

 quently by the supply of special kinds of stimulating foods 

 (p. 599). It would appear, therefore, that the metabolic activity 

 of -the ovaries is increased by these methods, and that the prob- 

 lematical internal secretion is elaborated in greater quantity. 



Lastly, it must not be forgotten that, whereas it is exceedingly 

 probable that the prooestrous changes of the uterus are brought 

 about by a specific excitant or hormone 3 arising in the ovaries, 



1 Heape, " The Menstruation and Ovulation of Macacus rhesus," Phil. 

 Trans., B., clxxxviii., 1897. 



2 Ries, " A Contribution to the Function of the Corpus Luteum," Amer. 

 Jour. Obatet., vol. xlix., 1904. 



3 Starling lias proposed the term hormone (from the Greek, 6p/j.au, I excite 

 or arouse) for such internal secretions or excitants of a chemical nature. 

 Thus, secretin, or the internal secretion of the duodenum, which excites 

 pancreatic secretion, is a hormone. See Starling, " The Chemical Cor- 

 relation of the Functions of the Body," Croonian Lectures, London, 1905 ; 

 also Lane-Claypon and Starling, loc. cit. 



