I must point out here that it must not be assumed that there exist only extreme males with scanty remnants of the female condition, extreme females with traces of the male, hermaphrodite or transitional forms, and wide gaps between these conditions. I am dealing specially with human beings, but what I have to say of them might be applied, with more or less modification, to nearly all creatures in which sexual reproduction takes place. Amongst human beings the state of the case is as follows: There exist all sorts of intermediate conditions between male and female--sexual transitional forms. In physical inquiries an “ideal gas” is assumed, that is to say, a gas, the behaviour of which follows the law of Boyle-Gay-Lussac exactly, although, in fact, no such gas exists, and laws are deduced from this so that the deviations from the ideal laws may be established in the case of actually existing gases. In the same fashion we may suppose the existence of an ideal man, M, and of an ideal woman, W, as sexual types although these types do not actually exist. Such types not only can be constructed, but must be constructed. As in art so in science, the real purpose is to reach the type, the Platonic Idea. The science of physics investigates the behaviour of bodies that are absolutely rigid or absolutely elastic, in the full knowledge that neither the one nor the other actually exists. The intermediate conditions actually existing between the two absolute states of matter serve merely as a starting-point for investigation of the “types” and in the practical application of the theory are treated as mixtures and exhaustively analysed. So also there exist only the intermediate stages between absolute males and females, the absolute conditions never presenting themselves. Let it be noted clearly that I am discussing the existence not merely of embryonic sexual neutrality, but of a permanent bisexual condition. Nor am I taking into consideration merely those intermediate sexual conditions, those bodily or psychical hermaphrodites upon which, up to the present, attention has been concentrated. In another respect my conception is new. Until now, in dealing with sexual intermediates, only hermaphrodites were considered; as if, to use a physical analogy, there were in between the two extremes a single group of intermediate forms, and not an intervening tract equally beset with stages in different degrees of transition. The fact is that males and females are like two substances combined in different proportions, but with either element never wholly missing. We find, so to speak, never either a man or a woman, but only the male condition and the female condition. Any individual, “A” or “B,” is never to be designated merely as a man or a woman, but by a formula showing that it is a composite of male and female characters in different proportions, for instance, as follows: { α M { β W A = { B = { { α´W { β´M