Thus understood, the “transformation” of pleasure into pain, and pain into pleasure, is only the translation into the order of affective psychology of the fundamental rhythm of life. The latter reduces itself to the ultimate fact of nutrition, consisting of two mutually interdependent processes, one of which implies the other, assimilation and dissimilation. Except in extreme cases, such as inanition and exhaustion on the one hand, and plethora on the other, in which one of the two processes prevails almost without counterpoise, they usually oscillate on either side of a medium, as pleasure and pain do on either side of an alleged neutral state. In physiology it happens that a very clear and easily verified phenomenon covers and hides a contrary phenomenon, so that the principal part of the occurrence is erroneously taken for the whole. Thus one knows that a muscle is heated by exercise, which seems to contravene the law of the transformation of energy, as the mechanical work done ought to consume a part of that mode of motion which we call heat. Béclard and several others after him have shown that there is a real lowering of temperature at the beginning of positive work, and that two opposite phenomena appear in the muscle when in action: one physical, absorbing heat and determining a cooling of the active muscle; the other chemical, producing a heating of the muscle. The latter masks the former. In the same way, the well-known experiments of Schiff have shown that the brain is heated when it receives impressions and elaborates them; it ought to grow cold, since it is doing work; but Tanzi’s experiments seem to establish the existence of alternating oscillations of cold and heat while the brain is at work. We recall these facts, though not in direct relation to our subject, to show that the coexistence of two opposite processes, the most apparent of which conceals the other, is not a chimera. There are frequently two simultaneous phenomena, of which the one is seen and not the other. According to this hypothesis, then, the conditions of existence of pleasure and pain are implied the one by the other, and always coexistent. What is expressed by consciousness is a _surplus_, and what is called their transformation is only a difference in favour of one or the other.[39] Footnote 39: This also seems to be the view adopted by Rutgers Marshall (_op. cit._). In the first place, he always considers “pleasure-pains” as connected states, pleasure being experienced “whenever the physical activity coincident with the psychic state to which the pleasure is attached involves the use of surplus stored force—the resolution of surplus potential into actual energy; or, in other words, whenever the energy involved in the reaction to a stimulus is greater in amount than the energy which the stimulus habitually calls forth.”—P. 204.