LACTATION 581 



growth is not specific i.e. not peculiar to any one kind of 

 mammal. Foa, says also that if the extract is heated to 110 

 the active substance is destroyed, and no result is produced by 

 injection. 1 



THE FACTORS WHICH ARE CONCERNED IN THE COMMENCE- 

 MENT OP MAMMARY SECRETION 



Since the growth of the mammary glands was apparently due 

 to a specific chemical stimulus arising in the foetus, it was natural 

 to suppose that the beginning of the actual secretory process 

 which marks the cessation of growth was caused by the removal 

 of this stimulus in other words, by the expulsion of the foetus. 

 In this connection it is interesting to note that abortion or 

 premature labour is often followed by the appearance of milk 

 in the breasts. 



The idea that lactation is due to the removal of an inhibition 

 appears to have been entertained first by Hildebrandt, 2 who put 

 forward the suggestion that the developing embryo exerts an 

 influence whereby the cells of the mammary gland are protected 

 from those autolytic disintegrative processes which are supposed 

 to occur during active secretion. That the act of secretion is 

 to be ascribed to autolytic processes of the gland, is, according 

 to Miss Lane-Clay pon and Starling, highly improbable, and 

 there is no evidence that the autolysis of the gland cells would 

 give rise to the specific constituents which characterise milk. 



Halban 3 has put forward the view that the specific stimulus 

 for mammary development arises in the placenta, while the 

 active secretion of the mammary glands is determined by the 

 expulsion or death of the placenta. 4 Keiffer, 5 on the other 

 hand, has entertained the contrary conception, that the secretion 

 of milk is due to a ferment elaborated in the placenta and trans- 



1 Foh,, " Sui Fattori che determinano 1'Accrescimento e la Funzione della 

 Ghiandola Mammaria," Arch, di Fis., vol. v., 1908. 



2 Hildebrandt, "Die Lehre von der Milchbildung," Hofmeistir's Bcitra-je, 

 vol. v., 1904. 



3 Halban, loc. cit. 



4 He points out that in cases of abortion the secretion of milk may not 

 begin until some days after the death of the child. This he believes to be 

 due to the circumstance that the placenta remained alive during the interval. 



5 Keiffer, " Recherches sur 1' Anatomic et la Physiologic de la Mamelle," 

 Bull, de la Soc. Beige de Gyn. et d'Obstet., 1901-2. 



