364 THE PHYSIOLOGY OF REPRODUCTION 



point to the conclusion that the presence of mature follicles is not 

 essential for the recurrence of heat. All the follicles approaching 

 ripeness were ruptured artificially by pricking three weeks and two 

 months before heat periods were due. In both cases heat appeared 

 at about the normal time. The inference was that the process of 

 follicular maturation and the phenomena of heat are both effects of 

 some further factor which must be sought for in the ovaries elsewhere 

 than in the ripe Graafian follicle. As Robinson points out, interstitial 

 tissue may be found in the bitch's ovaries, but according to 

 O'Donoghue 1 it is not always present in the ovaries of Mammals. 

 Robinson 2 expresses the view that the cells of the ruptured follicles 

 were not necessarily functionally interfered with, notwithstanding 

 the fact that they later developed into cells resembling those of 

 corpora lutea. He states further that in ferrets oastrus only occurs 

 when the ovaries contain follicles of a certain degree of development, 

 and that such follicles are present as long as oastrus persists. This 

 particular stage of development he calls the preinseminal stage when 

 the follicles "appear to take on the function of providing the 

 secretion which is responsible for the phenomena of prooestrum 

 and oestrus." 3 



It has already been shown that the breeding season, and 

 consequently the recurrence of the osstrous 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 frequently by the supply of 

 special kinds of stimulating foods (p. 635). It would appear, 

 therefore, that the metabolic activity of the ovaries is increased 

 by these methods, and that the problematical 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 4 arising in the ovaries, little 

 or nothing is known concerning the chain of causation leading to 

 that disturbed state of the nervous metabolism, the existence of 



1 O'Donoghue, "On the Corpora Lutea and the Interstitial Tissue in the 

 Ovary and in Marsupialia," Quar. Jour. Micr. Science, vol. Ixvi., 1916. 



J Robinson, " The Formation, etc., of Ovarian Follicles in Ferrets," Trans. 

 Roy. ,S'oc. Edin., vol. Hi., 1918. 



3 For further information see Bucura, " Zur Theorie der inneren Sekretion 

 des Eierstocks," Zent. fur Oyn., 1913. 



4 Starling has proposed the term hormone (from the Greek, 6p/xw, 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 Correlation of the 

 Functions of the Body," Croonian Lectures, London, 1905 ; also Lane-Claypon 

 and Starling, loc. rit. 



