By experiments of this sort on animals, it has been proved that the organochemical substances derived from the testis or ovary are of paramount importance for the development of secondary characters.
The evidence afforded by the experiments of Professor Eugen Steinach (of the Biological Institute in Vienna) on rats and guinea-pigs, is incontrovertible. When still very young, their own testes or ovaries were removed, i.e., they were castrated or sprayed. Then the reproductive masses of the opposite 'were implanted into their abdominal musculature. The reproductive elements of the implanted organs degenerated, but the other tissues proliferated.
So that later on, only that part of the graft which produces organochemical substances could function. If the grafts took successfully, the animals, though eunuchs, developed secondary characteristics, not those, however, of their original, but of that of the implanted organs. The masculinized, originally female animals, acquired a more robust build, and attempted to tread normal females, etc. In the feminized, originally male animals, the nipples developed, they showed a feminine coyness, took the female part in coitus, etc. Indeed, feminized male rats even suckled one or two young ones with maternal tenderness!
Thus the presence of either testes or ovaries decides the development of the characters, not only because of the production of egg-cells or sperm-cells, but also because of the specific organochemical substances which are poured by these organs into the circulation. These organochemical substances are responsible for the stimulus by which our whole bodily development, and our psyche as well, is dominated. Especially these organochemical substances govern the appearance of one or other type of secondary characters, as has been shown. Investigators have gone a step further and have inquired if they are not ultimately responsible for the appearance of the reproductive cells also, which is, after all, the most important point. Elsewhere too, new tissue-formation is often seen to be provoked by chemical stimuli, e.g., by toxins which are organochemical substances derived from bacteria and other micro-organisms.