382 HUMAN PHYSIOLOGY 



velopment. Sterility is only one result among many. 

 The contrast between the ox and the bull, the stallion 

 and the gelding is a familiar one. It is as much a con- 

 trast in temperament as in build. Animals without the 

 generative organs are said to lose, or rather never to 

 acquire, the secondary sexual characters. In man these 

 include the beard and the large larynx which accounts for 

 the average difference of an octave in the pitch of male 

 and female voices. After maturity has been attained 

 the changes that follow the operation are not striking. 



One of the marks of a male frog is a bulbous thumb. 

 It has been found that the early removal of the testes 

 prevents the development of this character and that it is 

 formed within a short time after the grafting into the 

 body of a testis from another frog. There could hardly 

 be a clearer demonstration of the power of hormones 

 liberated by one tissue to influence the metabolism of 

 another. If the transmitted effect were a nervous one 

 it would make a difference where the grafting had been 

 done ; in fact, it makes no difference at all. 



Some years ago it was argued that the decline of the 

 reproductive system in advanced life might have much to 

 do with the simultaneous deterioration of other organs, 

 especially the brain and cord. Vigor and efficiency might 

 be prolonged, it was thought, by introducing into the 

 body extracts from the reproductive glands of animals. 

 Trials were made upon senile subjects, who reported some 

 stimulation. But the results fell far short of the reju- 

 venation that had been hoped for and such as were 

 described have been credited for the most part to sug- 

 gestion. There has been no widely approved use of the 

 testicular extracts since the failure of the so-called Elixir 

 of Life. Ovarian extracts have been employed with ad- 

 vantage to abate distressing symptoms which follow the 

 removal of the female organs. 



The Spleen. This large organ is of a type which might 

 lead to the expectation that it could be shown to have 

 an internal secretion. The evidence, however, has not 



