In the 1915 edition of the Three Essays, a sentence has been removed. It has been replaced by a new passage with which we have since become acquainted. The new passage reads as follows: By an "instinct" is provisionally to be understood the psychical representative of an endosomatic, continuously flowing source of stimulation, as contrasted with a "stimulus", which is set up by single excitations coming from without. The key point in the erased sentence is the claim that there is first a basic life instinct that is not sexual per se and that the sexual quality of the libido is acquired only by linking this fundamental drive with parts of the body. At first glance, this does not seem to be such an important element in Freud's theory. Yet closer inspection reveals that it is, in fact, significant. To grasp its importance, it is necessary to study the collaboration between Freud and Jung.