Steinach has also in later experiments ("Geschlechtstrieb und echt Sekundäre Geschlechtsmerkmale als Folge der innerskretorischen Funktion der Keimdrusen," _Zentralblatt für Physiologie_, Bd. xxiv, Nu. 13, 1910) argued against any local nervous influence. He found in _Rana fusca_ and _esculenta_ that after castration in autumn the impulse to grasp the female persisted in some degrees and then disappeared, reappearing in a slight degree, however, every winter at the normal period of sexual activity. But when the testicular substance of actively sexual frogs was injected into the castrated frogs it exerted an elective action on the sexual reflex, sometimes in a few hours, but the action is, Steinach concludes, first central. The testicular secretion of frogs that were not sexually active had no stimulating action, but if the frogs were sexually active the injection of their central nervous substance was as effective as their testicular substance. In either case, Steinach concludes, there is the removal of an inhibition which is in operation at sexually quiescent periods. Speaking generally, Steinach considers that there is a process of "erotisation" (Erotisieurung) of the nervous center under the influence of the internal testicular secretions, and that this persists even when the primary physical stimulus has been removed. The experience of veterinary surgeons also shows that the sexual impulse tends to persist in animals after castration. Thus the ox and the gelding make frequent efforts to copulate with females in heat. In some cases, at all events in the case of the horse, castrated animals remain potent, and are even abnormally ardent, although impregnation cannot, of course, result.[8] The results obtained by scientific experiment and veterinary experience on the lower animals are confirmed by observation of various groups of phenomena in the human species. There can be no doubt that castrated men may still possess sexual impulses. This has been noted by observers in various countries in which eunuchs are made and employed.[9]