LACTATION 613 



death of the placenta.^ Keiffer,^ on the other hand, has entertained 

 the contrary conception, that the secretion of milk is due to a 

 ferment elahorated in the placenta and transferred to the maternal 

 circulation at the time of birth. These theories are based mainly 

 on clinical evidence of a somewhat questionable value. 



According to Miss Lane-Claypon and Starling's experiments, after 

 multiparous rabbits are injected with foetal extract milk is secreted 

 by the glands. This result was explained as follows : " The multi- 

 parous rabbit differs from a virgin rabbit in possessing ready-formed 

 alveoli,- i.e. secretory structures. On the theory which we have 

 adopted, the circulation of the mammary hormone should diminish 

 any secretion in these alveoli, g,nd should cause growth. In all our 

 experiments at least twenty-four hours elapsed between each two 

 injections. It is probable that the hormone was rapidly absorbed 

 from the injection, and was therefore present in the blood of the 

 animal, only for a certain fraction, say a few hours, out of the twenty- 

 four. While it was circulating it should cause building up of the 

 secreting cells. Directly, however, it ceased to circulate, the cells 

 would enter into dissimulative activity resulting in secretion. By 

 our injections, therefore, we are not able to imitate the continuous 

 stimulus of pregnancy. We are rather producing each day a 

 pregnancy of a few hours followed by a parturition. These factors 

 should therefore result in the production of milk in any animals 

 possessing the structures (i.e. the alveoli) which are capable of 

 secreting milk, and would therefore account for the secretion 

 of milk observed by us in all the cases where multiparous rabbits 

 were the objects of our experiment." 



It has been shown that in the fo3tus itself there is an increased 

 growth of the mammary glands during the last part of pregnancy; 

 while it is well known that a secretion is often formed in the glands 

 of the newly born. Halban has explained this secretion as the 

 result of removal of the inhibitory influence — that is to say, it is due 

 to the same circumstance as the secretion in the mother. Miss 

 Lane-Claypon and Starling point out that the complete change 

 which occurs in the environment of the newlyrborn animal must 

 induce equally profound changes in the metabolism, and there is 

 consequently no difficulty about the conclusion that the formation 

 of the mammary hormone ceases with the commencement of extra- 

 uterine life. 



The general conclusions at one time reached by these authors 



1 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 remains alive during the interval. 



2 Keififer, "Reoherches sur I'Anatomie et la Physiologie de la Mamelle," 

 Bull, de la Soc. Beige de Oyn. et d'Obstet., 1901-02. 



