Steinach found that, when sexually mature white rats were castrated, though at first they remained as potent as ever, their potency gradually declined; sexual excitement, however, and sexual inclination always persisted. He then proceeded to castrate rats before puberty and discovered the highly significant fact that in these also a quite considerable degree of sexual inclination appeared. They followed, sniffed, and licked the females like ordinary males; and that this was not a mere indication of curiosity was shown by the fact that they made attempts at coitus which only differed from those of normal males by the failure of erection and ejaculation, though, occasionally, there was imperfect erection. This lasted for a year, and then their sexual inclinations began to decline, and they showed signs of premature age. These manifestations of sexual sense Steinach compares to those noted in the human species during childhood.[6] The genesic tendencies are thus, to a certain degree, independent of the generative glands, although the development of these glands serves to increase the genesic ability and to furnish the impulsion necessary to assure procreation, as well as to insure the development of the secondary sexual characters, probably by the influence of secretions elaborated and thrown into the system from the primary sexual glands.[7] Halban ("Die Entstehung der Geschlechtscharaktere," _Archiv für Gynäkologie_, 1903, pp. 205-308) argues that the primary sex glands do not necessarily produce the secondary sex characters, nor inhibit the development of those characteristic of the opposite sex. It is indeed the rule, but it is not the inevitable result. Sexual differences exist from the first. Nussbaum made experiments on frogs (_Rana fusca_), which go through a yearly cycle of secondary sexual changes at the period of heat. These changes cease on castration, but, if the testes of other frogs are introduced beneath the skin of the castrated frogs, Nussbaum found that they acted as if the frog had not been castrated. It is the secretion of the testes which produces the secondary sexual changes. But Nussbaum found that the testicular secretion does not work if the nerves of the secondary sexual region are cut, and that the secretion has no direct action on the organism. Pflüger, discussing these experiments (_Archiv für die Gesammte Physiologie_, 1907, vol. cxvi, parts 5 and 6), disputes this conclusion, and argues that the secretion is not dependent on the action of the nervous system, and that therefore the secondary sexual characters are independent of the nervous system.