In the study of auto-erotism in another volume of these _Studies_ I have brought together some of the evidence showing that even in very young children spontaneous self-induced sexual excitement, with orgasm, may occur. Indeed, from an early age sexual differences pervade the whole nervous tissue. I may here quote the remarks of an experienced gynecologist: "I venture to think," Braxton Hicks said many years ago, "that those who have much attended to children will agree with me in saying that, almost from the cradle, a difference can be seen in manner, habits of mind, and in illness, requiring variations in their treatment. The change is certainly hastened and intensified at the time of puberty; but there is, even to an average observer, a clear difference between the sexes from early infancy, gradually becoming more marked up to puberty. That sexual feelings exist [it would be better to say 'may exist'] from earliest infancy is well known, and therefore this function does not depend upon puberty, though intensified by it. Hence, may we not conclude that the progress toward development is not so abrupt as has been generally supposed?... The changes of puberty are all of them dependent on the primordial force which, gradually gathering in power, culminates in the perfection both of form and of the sexual system, primary and secondary." There appear to have been but few systematic observations on the persistence of the sexual impulse in women after the menopause. It is regarded as a fairly frequent phenomenon by Kisch, and also by Löwenfeld (_Sexualleben und Nervenleiden_, p. 29). In America, Bloom (as quoted in _Medical Standard_, 1896), from an investigation of four hundred cases, found that in some cases the sexual impulse persisted to a very advanced age, and mentions a case of a woman of 70, twenty years past the menopause, who had been long a widow, but had recently married, and who declared that both desire and gratification were as great, if not greater, than before the menopause.