312 THE PHYSIOLOGY OF REPRODUCTION 



According to Loewy,^ tKe injection of testicular substance 

 into young capons causes the development of normal male 

 skeletal characters, as well as a better growth of the comb, &c. 

 Furthermore, Walker ^ states that, in two experiments in which 

 he injected sahne extract of cocks' testicles into two hens daily 

 for several months, the combs and wattles grew in size and 

 became more brightly coloured, reaching a maximum in five 

 months. When the injections were discontinued, the combs and 

 wattles underwent shrinkage and eventually became reduced 

 almost to their original condition. These experiments are of 

 interest, but they would seem to require confirmation before 

 the conclusion can definitely be drawn that the testicular 

 extract exerted an influence upon the sexual characters of the 

 hens, since the combs and wattles of fowls are normally subject 

 to periodic growth which may vary with the individual. 



It is stated that an imperfectly descended testicle (i.e. a 

 testicle which has failed to descend properly from the abdominal 

 cavity into the scrotal sac) in Man, notwithstanding the fact 

 that it may be without any spermatogenic function, is never- 

 theless of the greatest benefit to its possessor in virtue of its 

 influence over the metabohsm. " The secondary sexual 

 characters are a far more exact measure of the value of the 

 testicular tissues than are the presence of spermatozoa in 

 the external secretion. It may almost be said that a man's 

 male plumage is in direct proportion to the weight or amovmt 

 of testicular tissue present." ^ 



Perhaps the most conclusive evidence so far adduced in 

 support of the theory that the testis produces an internal secre- 

 tion is that supplied by Nussbaum * as a result of his experi- 

 ments upon frogs. At the approach of the breeding season 

 there is formed in the male frog a thickened pad of skin on the 

 first digit of each fore hmb associated with an increased muscular 



' Loewy, " Neuere Untersuohungen zur Physiologie der Gesohlechts- 

 organe," Ergebniaae der Phya., vol. ii., 1903. 



" Walker (0. E.) " The Influence of the Testis upon the Secondary Sexual 

 Characters of Fowls," Proc. Boy. Soc. Med., vol. i., 1908. 



' Corner, Diaeases of the Male Generative Organs/, Oxford, 1907. See 

 also McAdam Eocles, The Imperfectly Deacended Teatis, London, 1903. 



* Nussbaum, " Innere Sekretion uud NerveneinfluES,"ilfcrfcei and Bonnet, 

 Mrgeb. der Anat. und Entwich., vol. xv., 1905. 



