478 INTERNAL SECRETIONS 



which is perhaps inevitable, of attempting to simphfy our 

 problems arbitrarily, in considering the function of an endocrine 

 gland or of a system of such glands as something acting per se ; 

 in reality there are mutual relations existing between all the 

 internally secretory organs on the one hand, and between the 

 whole endocrine apparatus and the other parts of the organism 

 on the other. In physiology we are often compelled to think 

 too morphologically, and we attempt to localize functions in a 

 way which does not correspond with reality. 



It seems to me also that the desire to replace an endocrine 

 gland by the injection of an extract from the respective organ 

 arises from a too purely morphological attitude. In reality 

 it will never he possible to accomplish such a substitution tmtil 

 we are able to imitate quantitatively the rate and rhythm of the 

 secretory action of the gland. 



We mentioned above that sex hormones do not act in a way 

 that is specific for each separate species. But nevertheless 

 it seems possible that the endocrine action of the sex gland may 

 sometimes be responsible for differences between species. It 

 suffices to refer again to Morgan's experiments on hen-feather- 

 ing in breeds of fowls. Probably certain qualitative differences 

 between the testicle of the Sebright breed and that in other 

 breeds are the cause of the special distinguishing characters of 

 the Sebright. But possibly also different time and quantitative 

 factors in the endocrine function of the sex gland may determine 

 the distinguishing characters of the breeds. When considering 

 the great differences between human races in regard to the 

 relation between the length of the upper part of the body and 

 the lower extremities one cannot but think that the sex gland 

 or some other organ of internal secretion is a factor here. 

 There are races with relatively long extremities such as certain 

 natives of Australia and certain negroes; and those with rela- 

 tively short extremities like the Eskimos and various 

 Mongoloid races. Possibly also differences in the distribution 

 of the hair on the body are due to variation in endocrine 

 activity. The idea that racial differences in regard to body 

 growth may be dependent on differences in the development 

 of the endocrine glands, and especially the sex glands, has been 

 already expressed in general terms by Friedenthal (19 14, p. 140). 

 Keith (1919, 1922) also has attempted to elaborate a more 

 detailed theory on similar lines. 



