ACTION OF SEX HORMONES IN FOETAL LIFE 415 



VI. GENERAL DISCUSSION 



The precision and definiteness of the transformation of the 

 specific organ system, and the undoubted character of the pri- 

 mary cause of the transformation appears to offer a more defi- 

 nite basis than we have hitherto had for the analysis of the 

 origin and differentiation of some fundamental sex characteristics 

 of mammals. At the present time there is a general recognition 

 of the primary zygotic determination of sex in mammals ; we have 

 some scattering data on sex limited inheritance, a great deal of 

 miscellaneous information on the effects of castration, and a 

 little on the effects of cross transplantation of gonads. There is 

 also a large literature on hermaphroditism and pseudoher- 

 maphroditism of mammals. But these data are by no means 

 capable of arrangement in any general scheme. They are on the 

 whole exceedingly confusing in spite of the recent advances con- 

 cerning the zygotic character of the initial sex impulse,, and the 

 analyses of sex hormone action in post-foetal life. 



The free-martin gives us additional evidence of considerable 

 value concerning the problem of sex-determination and sex- 

 differentiation in mammals, especially in its suggestion that the 

 course of embryonic sex-differentiation is largely determined by 

 sex-hormones circulating in the blood. The evidential value of 

 this case is, however, limited, in the first place by the fact that 

 only the female is affected, — we have no information on the 

 reverse situation — and in the second place by the fact that we 

 cannot study separately the effect of early embryonic castration 

 of the female, but only as it is modified by the simultaneous 

 presence of male hormones. On the male side there is complete 

 absence of information as to the effects of early embryonic cas- 

 tration and the possible effect of the presence of female hormones^ 



5 A curious problem however presents itself in this connection viz : how it 

 happens that the sex-hormones of the mother do not affect the reproductive 

 system of the unborn sons. Steinach's results on feminization of infantile male 

 rats by castration and implantation of ovaries demonstrates the far reaching 

 effects of female sex hormones in the male system ; and we can hardly doubt that 

 even greater effects would result in embryonic life. It would appear probable, 

 therefore, that the embryo is in some way protected from the sex hormones 

 circulating in the mother's blood. Either there is cessation of production of sex 



