646 FKEDEKICK S. HAMMETT 



lead to the conclusion that the stimulus to mammary growth during preg- 

 nancy is derived mainly from the fetus. 



The Fetus and Milk Secretion. The clinical observations of Kehrer, 

 Cravin, Hofmann, de Sinety (a.) and others that milk secretion starts up 

 after the emptying of the uterus, either prematurely or by abortion, com- 

 bined with the observations of Hippocrates, Sinclair, Gessner, Deschamps, 

 Keller, Busch, and others, that milk secretion may often occur when the 

 fetus lies dead in the uterus, afford sufficient evidence to substantiate the 

 belief that the fertilized egg produces a substance acting as a stimulus to 

 milk secretion. The fact that the onset of a new pregnancy stops lactation, 

 as discussed by Munk and Kleinwachter, is too well known to need further 

 comment, and its significance in this connection is obvious. 



It is a fact, moreover, that Lane-Claypon and Starling were able to 

 induce secretion of milk in multiparous rabbits by the injection of fetal 

 extracts. They succinctly explain that their experiments could be con- 

 sidered as producing a brief pregnancy followed by parturition, which 

 naturally should be followed by the production of milk in the structures 

 prepared for it. 



The direct experimentation of MacKenzie is supported by the results 

 of Lane-Claypon and Starling and Biedl and Konigstein and shows almost 

 conclusively that fetal extracts do exert an inhibitory action on lactation. 

 In 1904 Hildebrandt proposed the theory that the uterine contents act 

 as a stimulus to mammary growth, but as an inhibitor to the mammary 

 autolytic changes which were supposed to be the essential precursors of 

 secretion. This idea he extended to the conception that, on the removal 

 of the uterine contents at birth, the inhibitory substance was likewise 

 removed and the initiation of the secretory process effected. This theory 

 coincides with the conditions as at present generally understood and elab- 

 orated in* detail by Biedl. 



The Fetal Membranes and Mammary Growth and 



Secretion 



Fellner has reported that the injection of extracts of the fetal mem- 

 branes has a slight stimulating effect on the mammary hyperplasia but 

 none on milk secretion. Close inspection of his results, however, shows 

 them to be too indeterminate to be conclusive, and the question of the 

 effect of this group of tissues on mammary activity is still open. 



The Testicle and Mammary Activity 



The results of the extensive implantation experiments carried on by 

 Halban (1905) led him to believe that the gonad tissue of either sex could 



