There are bound up with sex feeling and sex knowledge many customs, beliefs and habits, many legal statutes and social institutions, in the complex that is called sentiment, to which science looms as the sacrilegious ogre who devours romance. Without spending space upon the ravages of the sentimental idealist, certainly responsible for as much human disaster as the brutal realist, it is manifest that a revolution in sex standards and relations is inevitable as soon as the new doctrines filter down as matters of fact to the levels of the common intelligence. And surely, nothing else could be wished for in the world desired by all of us, the world ruled by intelligence, and intelligent good will. SEX CHEMISTRY A few general statements may be put down outright as material to go upon before we proceed to details. 1. Femininity and masculinity have a definite chemical basis in the reactions of the internal secretions of which they are the expression. That is to say, that just as a precipitate of chalk is formed when one throws some carbonate of soda into lime water, so the masculine and the feminine are to be looked upon as precipitates and crystallizations of a long series of linked chemical reactions in the fluids of the body, in which the internal secretions play a determining part. 2. Femininity and masculinity are expressions of the interplay of all the internal secretions. It used to be said by smart cats and accepted by the tabby cats, that a woman was a woman because of her ovaries alone. It is being said by some great discoverers of the day that man is a man because of his testes alone. Neither of these dogmas is true. There are individuals with ovaries who show every deviation from the feminine and there are individuals with testes who exhibit every variation from the masculine. The other endocrine glands are of equal importance. 3. There is no absolute masculine or absolute feminine. The ideals of the Manly Man and the Womanly Woman were erected by the blind ignorance of the nineteenth century illusionists, and a line drawn to cleave them. But indeed biologically there exists every transition between the masculine and the feminine. The explanation of these different sex types consists in the different admixtures of the internal secretions possible and actual. When we speak of the feminine we really mean the predominantly feminine. And when we speak of the masculine, we mean the mainly masculine. Between, all sorts of transitions are possible and occur. Man in relation to the internal secretions we have considered in reviewing the interstitial cells. To him, we shall return later. Let us turn now to that fascinating subject of the ages, Woman. What produces and maintains the Feminine? THE CAUSE OF SEX