7H 



surprising that, after some time, indications of the reHex may return. The 

 absence of it might depend, however, on the absence of afferent nervous impulses 

 from the testes. Steinach, then, took a number of castrated frogs and tested 

 for several consecutive days whether the reflex could be evoked. Having found 

 that it could not, he injected, into the dorsal lymph sac, the substance of 

 testes of frogs which had shown a marked reflex. After about twelve to 

 twenty-four hours the reflex began to appear, reached a maximum in two days, 

 and disappeared in three to four days, but could be brought back by renewed 

 injections. No increased excitability in any other reflex could be detected, 

 and it was noticed that the peripheral receptors, the swellings on the thumbs, 

 were enlarged after injection of testicular material. The effect of the testis of 

 the same species is the greatest, but it is not strictly specific, since that of 

 Rana fusca will act on Jt. esculenta. The result was still more marked in 

 cases, about 4 to 8 per cent, of the frogs caught, where the reflex was naturally 

 absent. Steinach believes that the action is exercised, primarily, on the central 

 nervous system, since injections of nervous matter from normal males caused the 

 return of the reflex in castrated males ; while the central nervous system of 

 castrated males had no such effect. The testes of males for two or three months 

 after the breeding season were devoid of action, so that the hormone is formed 

 periodically. It is supposed to act by depressing the activity of centres which 

 inhibit that for the clasp reflex. 



Further experiments were made on rats. Finding that feeding with testis 

 material was ineffective, autoplastic transplantation in animals of three to six 

 weeks old was performed. The testis was removed to various positions on the 

 inner surface of the abdominal muscles in some animals, and removed altogether 

 in other animals. In the -latter, no development of vesiculse seminales, prostate, 

 nor penis took place. In those in which the transplanted testis grew, the 

 development of the organs named was indistinguishable from that of normal 

 males, and the animals behaved, sexually, just as these. The hormone concerned 

 did not arise from the generative cells themselves, because they were not 

 developed in the transplanted testis, whereas the interstitial substance was fully 

 developed. 



Interesting observations have been made by Marshall and Hammond (1914) 

 on the effect of removal of the testes in Herdwick rams, where the operation is 

 found to stop the growth of horns. It is shown in these experiments that the 

 theory of Geoffrey Smith, according to which the effect of the testes is not due 

 to a hormone, but to a process explained by Ehrlich's side-chain theory of the 

 production of antitoxins, does not hold. 



Turning to the female, we find interstitial tissue in the ovary, as we saw in the 

 testis, to which the development of sexual characters is apparently due. The 

 changes taking place in the first stages of pregnancy have been shown by various 

 observers to depend upon the development of the corpora lutea, which are formed 

 in the place of the Graafian follicles after the ova have been extruded. The 

 reader may be interested to examine Figs. 253 and 254, which are copied from 

 Rene de Graaf's drawings of the follicles, which he discovered, and of the 

 corpora lutea. The effect of tlie latter on the development of the mammary 

 glands will be considered in the next section. In this place we may refer to 

 the work of Ancel and Bouin (1910), who showed that the growth of the uterus 

 is dependent upon that of the corpora lutea, since if these latter are formed in 

 any way, the first stages of the uterine hypertrophy occur, although there may 

 be no pregnancy. In this latter case the uterus returns to its original state. If 

 the Graafian follicles are ruptured artificially, it is found that the uterine 

 hypertrophy occurs, but only when a corpus luteum is formed. Further, if the 

 corpora lutea are destroyed by the cautery when uterine hypertrophy has 

 become obvious, the hypertrophy ceases to increase and rapidly disappears. 



From the experiments of Marshall and Jolly (1908) and those of Nattrass 

 (1910), it follows that a transplanted ovary, when it continues to live, is capable 

 of maintaining the sexual characters of the individual. 



With regard to transplantations of the ovary, Guthrie (1908) believes that 



