If the suckling could express himself, he would probably recognize the act of sucking at his mother's breast as the most important thing in life. He is not so far wrong, for in this one act he satisfies two great needs of life. With no small degree of surprise we learn through psychoanalysis how much of the physical significance of this act is retained through life. The sucking at the mother's breast becomes the term of departure for all of sexual life, the unattained ideal of later sex gratification, to which the imagination often reverts in times of need. The mother's breast is the first object for the sexual instinct; I can scarcely bring home to you how significant this object is for centering on the sexual object in later life, what profound influence it exerts upon the most remote domains of psychic life through evolution and substitution. The suckling, however, soon relinquishes it and fills its place by a part of his own body. The child sucks his thumb or his own tongue. Thereby he renders himself independent of the consent of the outer world in obtaining his sensual satisfactions, and moreover increases the excitement by including a second zone of his body. The erogenous zones are not equally satisfactory; it is therefore an important experience when, as Dr. Lindner puts it, the child while touching his own body discovers the especially excitable genitals, and so finds the way from sucking to onanism.
Through the evaluation of sucking we become acquainted with two decisive characteristics of infantile sexuality. It arises in connection with the satisfaction of great organic needs and behaves _auto-erotically_, that is to say, it seeks and finds it objects on its own body. What is most clearly discernible during the taking in of food is partially repeated during excretion. We conclude that the nursling experiences pleasure during the excretion of urine and the contents of the intestine and that he soon strives to arrange these acts in a way to secure the greatest possible amount of satisfaction by the corresponding excitement of the erogenous membrane zones. Lou Andreas, with her delicate perceptions, has shown how at this point the outer world first intervenes as a hindrance, hostile to the child's desire for satisfaction--the first vague suggestion of outer and inner conflicts. He may not let his excretions pass from him at a moment agreeable to him, but only when other persons set the time. To induce him to renounce these sources of satisfaction, everything relating to these functions is declared indecent and must be concealed. Here, for the first time, he is to exchange pleasure for social dignity. His own relation to his excretions is originally quite different. He experiences no disgust toward his faeces, values them as a part of his body from which he does not part lightly, for he uses them as the first "present" he can give to persons he esteems particularly. Even after education has succeeded in alienating him from these tendencies, he transfers the evaluation of the faeces to the "present" and to "money." On the other hand, he appears to regard his achievements in urination with especial pride.