ORGANS OF INTERNAL SECRETION 333 



ovaries obtained from other dogs were grafted in abnormal 

 positions (e.g. between the abdominal muscular layers or on 

 the ventral border of the peritoneal cavity). The grafts seem 

 to have become attached, and to have survived for a sufficiently 

 long period to exercise an influence over the generative system ; 

 but they eventually underwent considerable fibrous degenera- 

 tion, as the post-mortem evidence afterwards showed. 



As a result of these experiments it may probably be con- 

 cluded that the enhanced activity which the ovaries exhibit 

 during the final stages of follicular development is accompanied 

 by metabolic changes which result in an increase in the pro- 

 duction of the ovarian secretion, and that this phenomenon is 

 the main factor in the periodic recurrence of heat and menstrua- 

 tion. 1 It has been observed that, not only are the internal 

 and external generative organs affected at these periods, but 

 there is also a distinct hypertrophy of the breasts, and this, 

 as Miss Lane-Claypon and Starling 2 have pointed out, is pro- 

 bably due also to an increase in the ovarian metabolism. 3 



There is a certain amount of direct evidence that heat and 

 menstruation are brought about by an internal secretion 

 elaborated by the ovaries. It has been found that the injection 

 of fresh ovarian extract obtained from animals which are " on 

 heat " may produce in anoestrous animals a transient congestion 

 of the external generative organs resembling that of the normal 

 procestrous condition. 4 Miss Lane-Claypon and Starling also 



1 As already pointed out, menstruation and ovulation are not necessarily 

 associated. It is probable, however, that the ovarian metabolism is increased 

 at the menstrual periods, although there may not always be any follicles 

 present in a sufficiently mature condition to admit of ovulation occurring 

 in the oestrous periods which normally follow them. 



2 Lane-Claypon and Starling, " An Experimental Inquiry into the Factors 

 which Determine the Growth and Activity of the Mammary Glands," Proc. 

 Roy. Soc., B., vol. lxxvii.,.1906. 



3 According to Pearl and Surface ("The Nature of the Stimulus which 

 causes a Shell to be formed on a Bird's Egg," Science, New Series, vol. xxix., 

 1909), the stimulus which excites the activity of the shell-secreting glands 

 in the fowl's oviduct is mechanical, being brought about by a strictly local 

 reflex. The shape of the egg is determined by the muscular activity of the 

 cells of the oviduct (Pearl, " Studies on the Physiology of Reproduction 

 in the Domestic Fowl : I. Regulation in the Morphogenetic Activity of the 

 Oviduct," Jour, of Exp. Zool., vol. vi., 1909). 



4 Marshall and Jolly, loc. cit. 



