RELATING TO SECONDARY SEXUAL CHARACTERS. 87 



he does not agree with the two former observers. His results show that 

 castration at the breeding-season is rapidly followed by the loss of the 

 outer papillated layer of the thumb-pads, but castration at any other 

 season does not have "any marked effect," the papillae remaining for 

 5 months and more in the same condition as at the time of castration. 

 The essential point here, however, is that the excessive and even 

 special development at the breeding-season does not take place nor is 

 again assumed (apparently), if castration has taken place at some 

 other time of the year. 



Smith and Schuster's attempts to transplant the testes into other 

 males or females were unsuccessful, as the testes degenerate after a 

 time. Auto-transplantation of the testes were more successful. 



Removal of the ovary had no effect on the thumbs of the female, 

 and even the injection of testes extracts into such females did not 

 cause them to develop pads. Nussbaum and Meisenheimer had 

 found that transplantation of pieces of the testes, and even injection 

 of testes extract, into castrated frogs caused an enlargement of the 

 thumb-pads. Smith shows that this conclusion rests on uncritical 

 evidence. At any rate, his own more carefully planned experiments 

 extending over the year show that the results obtained by Nussbaum 

 and by Meisenheimer may be accounted for on other grounds than the 

 effect of the injection or implantation. 



The following statement by Smith is not without interest, since it 

 bears directly on an important question as to how internal secretions 

 may produce their effects. 



"The deduction, therefore, which has been unduly based on Nussbaum's 

 experiments, that the testis of the frog contains an internal secretion, which, 

 on being circulated in the blood, calls for the development of the secondary 

 sexual characters, either with or without the mediation of the nervous system, 



is without experimental foundation The fact that the developmental 



cycle of the thumb depends for its normal course on the presence of normal 

 living testicular tissue can be equally well explained on the theory that the 

 testicular cells enter into a chain of metabolic processes in the body which do 

 not pursue their normal course in the absence of the testicular cells. This 

 disturbance of the normal metabolic processes of the body, resulting in the 

 failure of the metabolic organs of the body to give rise to their normal prod- 

 ucts in normal quantities, may have the result of inhibiting the further devel- 

 opment of the secondary sexual characters. The development of these latter 

 characters may depend, therefore, not directly on the action of an internal 

 secretion or hormone derived from the gonad, but on the elaboration of other 

 products in other organs of the body in their due proportions. These sub- 

 stances may be tentatively called 'sexual formative substances/ but we have 

 no reason for supposing that they are entirely devoted to sexual or reproduc- 

 tive purposes, and that they take no part in the ordinary metabolic processes 

 of the body." 



The arbitrary distinctions that Smith here sets up do not seem to 

 me to contribute anything to the situation, and in fact in the end it 

 amounts to practically the same thing whether the hormone acts 



