By this term is understood the appearance of the sexual appetite, or even of love, at an abnormal age. Infantile paradoxy is, however, very different to senile paradoxy. Infantile paradoxy must not be confounded with certain forms of masturbation, to which we shall return. Some races, especially in the tropics, have a much earlier sexual development than others; depending more on race than climate. In some, sexual maturity occurs in boys between the age of twelve and fourteen, and in girls between nine and ten years, while in others the former are hardly mature at twenty and the latter before seventeen or eighteen. Again, individual variations may be very great in the same race. But, owing to hereditary satyriasis or nymphomania, we sometimes in our own country see sexual appetite appear in children of eight, seven, or even three or four years of age, in a spontaneous manner without any external excitation. Lombroso mentions the case of a girl three years old who had an irresistible tendency to onanism. I have myself observed the two following cases: (1). A boy of seven years, the son of a brothel keeper, and a kind of satyr who committed great excesses, began spontaneously to attack little girls of his own age or even younger. He was so artful that all means failed in curing him of this habit, and he was sent to an asylum of which I was superintendent. He then tried to renew his exploits with a boy older than himself. He was also idle and disposed to all kinds of folly. He did not, however, attempt to copulate with adult women or men. His sexual organs were absolutely infantile, without any abnormal development. His paradoxy was thus of cerebral origin. (2). _A girl of nine years was brought to my office addicted to self-abuse. Upon examination, I found this child highly neurotic, the major part of her life had been under unhygienic atmosphere, case history, father psychopathic, had been in an insane asylum, mother ænemic. The child was sent to a state institution for girls and improved remarkably._ In this case I was told that there was no hereditary taint, but such statements prove nothing. Individuals of this kind generally become criminals, or else give themselves up to masturbation or prostitution. Occasionally, the sexual appetite may be preserved for a long time in old men, or reappear for a time, with or without sexual power, but as a rule, the paradoxy of old men is the initial symptom of _senile dementia_. As this disorder is only commencing when sexual excitation occurs, it is not noticed, and the patient is regarded as an immoral, vicious or criminal individual. I have seen a patient of this kind masturbate openly in an asylum, so great was his sexual excitation.