94 THE NATURE OF LIFE ' 



which had received ovaries in place of j 



testes took on the characters of the fe- ! 



male, including the more graceful form, ! 



softer fur, larger nipples and even the ; 



habits of the female. The breasts se- \ 



creted milk and these animals suckled 

 young. 



The females which received testes in 

 place of ovaries showed less effect but 

 acquired to a considerable extent the 

 heavier build, larger head, coarser fur 

 and the habits of the male. 



In all these cases the gland produces 

 a small amount of substance, called a 

 hormone, which influences development. 

 There are doubtless a large number of 

 such hormones. Their influence on bod- 

 ily form and on mental states is just be- 

 ginning to be more fully appreciated. 

 Doubtless the immediate future will wit- 

 ness rapid advances in this field of study. 



The question arises whether we can 

 introduce hormones, or artificial substi- 

 tutes for them, into the body and so in- 

 fluence development. There seems to be 



