In boys, the sexual appetite is often prematurely awakened, excited in unnatural ways by bad example. Moreover, it varies enormously in different individuals, a point to which we shall return when dealing with pathology. Leaving aside unnatural appetites and abnormal forms of sexual instinct we shall describe here its most spontaneous and normal form. =Puberty. Awakening of the Sexual Instinct in Boys.=--Sooner or later in different individuals, the boy pays attention to his erections, which are at first produced in a reflex and involuntary manner. Mental development and reflection, so precocious in man, are causes which draw attention to the differences of the sexes before the sexual appetite is developed. It is, however, the first signs of this appetite which concentrate the attention on these differences, for in their absence, the boy is more indifferent to them than to the straight or crooked form of a nose. Man has the habit of passing by without notice anything which does not interest him, and this is why we find, in individuals whose sexual appetite is developed late or feebly, an indifference and ignorance in these matters which appear almost incredible to those whose sexual appetite is precocious and violent; while, on the contrary, the lively interest which the latter show in everything concerning the sexes appears foolish and absurd to the sexually indifferent. The pairing of animals, even of insects, awakens a curious interest in those whose sexual dispositions are strong and precocious; they comprehend very quickly the reason and are led to draw analogies with their own sensations in the same domain. The aspect of the female sex has, however, a much stronger action still on the normal man. But here is produced a peculiar phenomenon. What especially excites the boy in the aspect of the female sex is anything unusual; the sight of certain parts of the skin which are normally covered, the clothes or ornaments, particular odors, women whom the boy is not accustomed to see, etc. It is for this reason that brothers and sisters do not excite, or excite very little, their reciprocal sexual appetite, at least if there are no anomalies or exceptional exhibitions. The sexual appetites of boys among savage peoples who live naked is hardly at all excited by naked girls; on the other hand, it is strongly excited by those who are clothed or ornamented in a peculiar manner. The sexual appetite of a Mahometan is strongly excited by the nudity of the feminine face, that of the European by that of a woman's legs, because women are accustomed to veil their faces in the first case and their legs in the second. These are naturally only relative differences. When the sexual appetite of man is violent and unsatisfied woman excites it in a general way, if she is not too old or repulsive.