Now I shall present to you what is most easily recognizable in the sexual life of the child. At first, for the sake of convenience let me explain to you the conception of the libido. Libido, analogous to hunger, is the force through which the instinct, here the sex instinct (as in the case of hunger it is the instinct to eat) expresses itself. Other conceptions, such as sexual excitement and satisfaction, require no elucidation. You will easily see that interpretation plays the greatest part in disclosing the sexuality of the suckling; in fact you will probably cite this as an objection. These interpretations proceed from a foundation of analytic investigation that trace backwards from a given symptom. The suckling reveals the first sexual impulses in connection with other functions necessary for life. His chief interest, as you know, is directed toward the taking in of food; when it has fallen asleep at its mother's breast, fully satisfied, it bears the expression of blissful content that will come back again in later life after the experience of the sexual orgasm. That of course would be too slight evidence to form the basis of a conclusion. But we observe that the suckling wishes to repeat the act of taking in food without actually demanding more food; he is therefore no longer urged by hunger. We say he is sucking, and the fact that after this he again falls asleep with a blissful expression shows us that the act of sucking in itself has yielded him satisfaction. As you know, he speedily arranges matters so that he cannot fall asleep without sucking. Dr. Lindner, an old pediatrist in Budapest, was the first one to ascertain the sexual nature of this procedure. Persons attending to the child, who surely make no pretensions to a theoretic attitude, seem to judge sucking in a similar manner. They do not doubt that it serves a pleasurable satisfaction, term it naughty, and force the child to relinquish it against his will, and if he will not do so of his own accord, through painful measures. And so we learn that the suckling performs actions that have no object save the obtaining of a sensual gratification. We believe that this gratification is first experienced during the taking in of food, but that he speedily learns to separate it from this condition. The gratification can only be attributed to the excitation of the mouth and lips, hence we call these parts of the body _erogenous zones_ and the pleasure derived from sucking, _sexual_. Probably we shall have to discuss the justification of this name.