INTERNAL SECRETIONS 93 



were much more fully developed than in castrated control animals. 

 More recently Pezard made intraperitoneal injections of pigs' 

 testes into a capon, and induced a growth of the comb and other 

 erectile structures on the head. The fact that one-sided castration 

 produces no effect on the symmetry of the secondary sexual 

 characters {e.g. the horns of the Herdwick ram) or upon the 

 development of the accessory generative glands {e.g. the vesiculae 

 and prostate in the hedgehog) is further evidence that the gonads 

 act through hormones circulating in the blood rather than locally 

 through the nervous system. 



The question as to the seat of production of the testicular 

 hormone is not yet definitely solved, but in mammals at least 

 it is widely believed that it is elaborated by the interstitial cells 

 rather than by the spermatogenetic tissue or other cells belong- 

 ing to the tubules. The evidence on which this conclusion is 

 based is derived from the study of cryptorchid or undescended 

 testicles in which no spermatogenetic tissue is present, and from 

 vasectomy and x-ray experiments, and from grafts in which 

 the interstitial tissue only appeared to have been functionally 

 active. 



Thus in Tandler and Gross's investigation on the roe-buck, 

 the animal's testes were subjected to the x-rays, and as a con- 

 sequence all the spermatozoa and spermatogenetic cells were 

 destroyed, but the interstitial tissue remained unaffected. In 

 the breeding season the horns grew in an entirely normal manner, 

 and so distinguished the " Rontgen buck " from the castrated 

 buck in which the horns did not undergo the usual periodic 

 development. Bouin and Ancel were the first to show that when 

 the vasa deferentia in the horse and other animals are ligatured 

 or cut, although the spermatogenetic tissue of the testis ceases 

 to be functional and gradually undergoes atrophy, the interstitial 

 cells do not atrophy. Indeed, it is affirmed by Steinach and 

 others that under these conditions the interstitial cells even 

 hypertrophy. This result is not clearly understood, but it may 

 be that tubules degenerate owing to their contents being unable 

 to escape, and that consequently the intervening cells are pro- 

 vided with space to hypertrophy associated with an increased 

 vascularisation. Moreover, as Copeman also showed, under the 

 conditions of such experiments, the presence of the interstitial 

 cells only, suffices for the development of the secondary sexual 



