I will now tell you the most clearly recognizable of the child’s sexual activities. It will be expedient if I first introduce you to the term LIBIDO. In every way analogous to _hunger_, Libido is the force by means of which the instinct, in this case the sexual instinct, as, with hunger, the nutritional instinct, achieves expression. Other terms, such as sexual excitation and satisfaction, require no definition. Interpretation finds most to do in regard to the sexual activities of the infant, as you will easily perceive; and no doubt you will find it a reason for objections. This interpretation is formed on the basis of analytic investigation, working backwards from a given symptom. The infant’s first sexual excitations appear in connection with the other functions important for life. Its chief interest, as you know, is concerned with taking nourishment; as it sinks asleep at the breast, utterly satisfied, it bears a look of perfect content which will come back again later in life after the experience of the sexual orgasm. This would not be enough to found a conclusion upon. However, we perceive that infants wish to repeat, without really getting any nourishment, the action necessary to taking nourishment; they are therefore not impelled to this by hunger. We call this action “_lutschen_” or “_ludeln_” (German words signifying the enjoyment of sucking for its own sake—as with a rubber “comforter”); and as when it does this the infant again falls asleep with a blissful expression we see that the action of sucking is sufficient in itself to give it satisfaction. Admittedly, it very soon contrives not to go to sleep without having sucked in this way. An old physician for children in Budapest, Dr. Lindner, was the first to maintain the sexual nature of this procedure. Nurses and people who look after children appear to take the same view of this kind of sucking (_lutschen_), though without taking up any theoretic attitude about it. They have no doubt that its only purpose is in the pleasure derived; they account it one of the child’s “naughty tricks”; and take severe measures to force it to give it up, if it will not do so of its own accord. And so we learn that an infant performs actions with no other object but that of obtaining pleasure. We believe that this pleasure is first of all experienced while nourishment is being taken, but that the infant learns rapidly to enjoy it apart from this condition. The gratification obtained can only relate to the region of the mouth and lips; we therefore call these areas of the body _erotogenic zones_ and describe the pleasure derived from sucking (_lutschen_) as a _sexual_ one. To be sure, we have yet to discuss the justification for the use of this term.