ON SOMATIC SEX-CHARACTERS 97 



been proved in 1874 when Goltz and Ewald l 

 removed the whole of the lumbo-sacral portion of 

 the spinal cord of a bitch and found that the 

 mammae in the animal developed and enlarged in 

 the usual way during pregnancy and secreted milk 

 normally after parturition. Ribbert 2 in 1898 trans- 

 planted a milk gland of a guinea-pig to the neighbour- 

 hood of the ear, and found that its development 

 and function during pregnancy and at parturition 

 were unaffected. The effective stimulus, therefore, 

 is not conveyed through the nervous system, but 

 must be a chemical stimulus passing through the 

 vascular system. 



Physiologists, however, are not equally in agree- 

 ment concerning the source of the hormone which 

 regulates lactation. Starling and Miss Lane-Claypon 

 concluded from their experiments on rabbits that 

 the hormone originated in the fetuses themselves 

 within the pregnant uterus. In virgin rabbits it is 

 difficult to find the milk glands at all. When found 

 the nipple is minute and sections through it show the 

 gland to consist of only a few ducts a few millimetres 

 in length. Five days after impregnation the gland 

 is about 2 cm. in diameter. Nine days after im- 

 pregnation the glands have grown so much that the 

 whole inner surface of the skin of the abdomen is 

 covered with a thin layer of gland tissue. In six 

 cases by injecting subcutaneously extracts of foetus 

 tissue Starling and Lane-Claypon obtained a certain 

 amount of growth of the milk glands. The hormone 

 in the case of the pregnant rabbit is of course acting 

 continuously for the whole period of pregnancy, 

 while the artificial injection took place only once 



1 Pfliigers Archiv, ix., 1874. 2 Fortschritte der Medicin, Bd. 7. 



G 



