LACTATION 579 



tion of an organ of complicated structure — the placenta — the 

 function of which is to nourish the developing young. The 

 question arose, therefore, as to whether the foetus or either of the 

 above-mentioned organs was not the direct source of formation 

 of a hormone or chemical excitant which, after circulating in the 

 blood stream, acted as a stimulus to mammary growth. 



It has been shown that the ovaries of rats can be removed 

 at any time during the second hali of pregnancy (or somewhat 

 earher) without interfering with the course of foetal develop- 

 ment or mammary growth, and, moreover, that lactation may 

 take place normally after the ovaries have been thus extirpated.^ 

 It is evident, therefore, that though the ovaries may represent 

 the original source of the stimulus necessary for mammary 

 hypertrophy, they are not essential for the continuance of the 

 process, and exercise no sort of control over the final stages 

 which precede the secretion of milk.^ 



Furthermore, it has been shown that the mammary glands 

 undergo normal development in cases of extra-uterine foetation 

 in which the growth of the uterus is relatively small. This 

 observation clearly indicates that the source of the stimulus in 

 question is not to be sought in the hypertrophied uterus. A 

 consideration of these and other facts led Miss Lane-Claypon 

 and Starling to the conclusion that one or other of the products 

 of conception (i.e. either the foetus or placenta), or possibly both, 

 were the seats of origin of the specific chemical stimulus which 

 brought about mammary growth. 



Halban * had already formed the opinion, chiefly on clinical 

 grounds, that the specific stimulus arose mainly in the chorionic 

 vilh and placenta. 



More recently Ancel and Bo: in have laid stress on the close 

 parallelism between the development and regression of the cor- 

 pora lutea and mammary glands respectively in the rabbit. 



* Marshall and Jolly, "Contributions," &c., Phil. Trans., B., vol. cxoviii., 

 1905. 



^ Cf. Foges, " Beitrage zu der Beziehung von Mamma und Genitale," 

 Wien. klin. Woch., 1908, No. 5. Grunbaum (Deut. med. Wochenachr., 

 1907, No. 20) has shown that mammary secretion may also occur after 

 hysterectomy. 



' Halban, " Die innere Sekretion von Ovarium und Placenta und ihre 

 Bedentuug fur die Function der MilchdrUse," Arch. f. Gyndk., vol. Ixxv., 1905. 



