Such are the tendencies which, in my opinion, are the roots of all simple or compound emotions, present, past, or future. This assertion will be justified or invalidated by the following studies. CHAPTER I THE INSTINCT OF CONSERVATION IN ITS PHYSIOLOGICAL FORM. _Hypothesis regarding the relation between the nutritive organs and the brain—Perversion of the instincts relating to nutrition—Pathology of hunger and thirst—Proofs furnished of the priority of these tendencies in relation to pleasure and pain—Facts in support of this—Negative tendency; disgust—Its biological value as a protective instinct._ The above title may seem quite unconnected with psychology, or at least of a nature to throw little light on our subject. This is not the case. This group of tendencies—for we have seen that the conservative instinct is a sum, a total—represents the principal factors in what is called cœnæsthesia, the very soil on which emotional life grows and bears fruit. Moreover, the nutritive instincts have their pathology, which enables us to watch, not the genesis (which would be impossible) of new tendencies, but a radical transformation, a complete change of orientation, whose effects are easily observable and instructive. In a normal state the instincts are presented to us as ready made and in action; we cannot, either in ourselves or in others, go back to that distant and obscure period when the unconscious impulse, the blind tendency, showed itself for the first time, without antecedent experience of the pleasant or unpleasant consequences. So that our affirmation that tendency is antecedent to pleasure and pain may be stigmatised as merely theoretical so long as we are unable to cite indubitable facts in demonstration of it. These facts we are about to furnish. I.