368 INTERNAL SECRETION 



We are justified in assuming from the evidence which has 

 been brought forward that the stigmata of sex are, from their 

 earliest beginnings, dependent upon the genital gland, and that 

 for this reason they are very rightly termed " secondary." That 

 they attain to complete development by the agency of the cells 

 of generation only, is a point which has never been questioned. 



That the somatic differences between the sexes are dependent 

 upon their genital glands is shown, in animals, by the signs 

 which accompany the periodic recurrence of the rutting period, 

 and in man by the phenomena of puberty. The maturity of the 

 organs of generation at the rutting period is accompanied by 

 remarkable changes in the structure and functional capacity of 

 the body, which last only so long as the increased activity of the 

 reproductive organs is maintained. Every one is familiar with 

 the brilliant coloration of the plumage, the rich, full song, and 

 the activity and love-play of birds in the mating season. In 

 other classes, the amphibia, for instance, the males and females 

 are distinguished by certain peculiarities during the mating 

 season in the spring and early summer. The male water- 

 salamander acquires a head-comb, the male batrachian, callosities 

 upon the thumbs. . 



Nussbaum's careful experiments have proved beyond all 

 doubt that, in the case of animals with recurrent mating season, 

 the internal secretion of the genital gland of the male has an 

 enormous influence, not only upon the genital apparatus, but 

 upon the rutting organs which are closely related to the processes 

 of reproduction. In the brown land-frog, Rana fusca, the seminal 

 vesicles, the thumb callosities, and certain of the fore-arm muscles 

 undergo annual cyclic changes which accord \vith the rutting 

 season. These organs swell up, become hypertrophied, and at 

 the expiration of the spawning period undergo involution. 



The removal of the testicle from one side has no effect upon 

 the rutting organs, but if castration is performed during the 

 period of sexual quiescence, the rutting organs will not develop 

 at the next rutting season. Nussbaum introduced portions of 

 testicle into the dorsal lymph-space of such castrated male frogs, 

 with the result that the rutting organs began to hypertrophy in 

 exactly the same way as those of uncastrated animals. The 

 portions of testicle did not heal in but gradually became resorbed, 

 while at the same time the seminal vesicles, thumb-callosities and 

 forearm muscles diminished in size. These experiments prove 

 beyond any manner of doubt that the testicles supply a material 

 to the economy which promotes development ; in other words, they 

 elaborate an assimilatory hormone. 



In the course of further experiments, Nussbaum discovered 

 that after resection of the nerve of one fore-arm, neither the 

 muscle of that fore-arm nor the papillae and glands of the thumb- 

 callosity of that side underwent hypertrophy at the spawning- 



