from the habitual introduction of pleasure-producing poisonous substances (alkaloids.) THE THEORY OF THE LIBIDO These assumptions concerning the chemical basis of the sexual excitement are in full accord with the auxiliary conception which we formed for the purpose of mastering the psychic manifestations of the sexual life. We have determined the concept of _libido_ as that of a force of variable quantity which has the capacity of measuring processes and transformations in the spheres of sexual excitement. This libido we distinguished from the energy which is to be generally adjudged to the psychic processes with reference to its special origin and thus we attribute to it also a qualitative character. In separating libidinous from other psychic energy we give expression to the assumption that the sexual processes of the organism are differentiated from the nutritional processes through a special chemism. The analyses of perversions and psychoneuroses have taught us that this sexual excitement is furnished not only from the so-called sexual parts alone but from all organs of the body. We thus formulate for ourselves the concept of a libido-quantum whose psychic representative we designate as the ego-libido; the production, increase, distribution and displacement of this ego-libido will offer the possible explanation for the observed psycho-sexual phenomena. But this ego-libido becomes conveniently accessible to psychoanalytic study only when the psychic energy is employed on sexual objects, that is when it becomes object libido. Then we see it as it concentrates and fixes itself on objects, or as it leaves those objects and passes over to others from which positions it directs the individual's sexual activity, that is, it leads to partial and temporary extinction of the libido. Psychoanalysis of the so-called transference neuroses (hysteria and compulsion neurosis) offers us here a reliable insight. Concerning the fates of the object libido we also state that it is withdrawn from the object, that it is preserved floating in special states of tension and is finally taken back into the ego, so that it again becomes ego-libido. In contradistinction to the object-libido we also call the ego-libido narcissistic libido. From psychoanalysis we look over the boundary which we are not permitted to pass into the activity of the narcissistic libido and thus form an idea of the relations between the two. The narcissistic or ego-libido appears to us as the great reservoir from which the energy for the investment of the object is sent out and into which it is drawn back again, while the narcissistic libido investment of the ego appears to us as the realized primitive state in the first childhood, which only becomes hidden by the later emissions of the libido, and is retained at the bottom behind them.