HORMONES 57 



the mammary glands into activity. To test this 

 hypothesis, they made an extract from a num- 

 ber of rabbit embryos and injected this sub- 

 cutaneously into virgin female rabbits. The 

 result of this treatment was that the mammary 

 glands of these rabbits underwent the prepar- 

 atory growth that would have been character- 

 istic of them had there been a real pregnancy. 

 Further evidence of the same kind is furnished 

 by the interesting case of the Blazek sisters, 

 to quote from Howell. These twins were joined 

 like the Siamese twins; they had a common 

 circulation but separate nervous systems. Preg- 

 nancy and parturition in one was followed 

 by a secretion of the mammary glands of 

 both. Thus it seems quite clear that the devel- 

 oping mammalian embryo gives out hormones 

 to the maternal body and that these hormones 

 excite activity in those maternal organs which 

 are to serve the young after birth. It would 

 be superfluous to point out here the signifi- 

 cance of these relations to the practice of 

 dairying. In my opinion a step has been taken 

 in the laboratory which when properly fol- 

 lowed up may revolutionize our methods of 

 dealing with the milch cow. The time may 

 not be very distant when an extract of calf 



