Although these broad facts are universally recognised, there is nevertheless no unanimity with regard to their interpretation. It may be held, on the one hand, that the perception of those objective conditions which call forth pleasure is accompanied by a tendency to movement. That, conversely, movement creates pleasure would thus be the result of an association. But it may also be contended that the functional enhancement, the stimulation itself, when present to consciousness, is perceived as pleasure, and that the feeling-tone created by movement is thus not indirect and secondary, but, on the contrary, is a typical pleasure. We do not by any means deny the influence which associative processes exercise on all our feelings and on the activities connected with them. As has been shown by Darwin, animals as well as primitive man have earned their chief enjoyment, outside their delight of warmth and repose, by violent actions, such as hunting, war, and pairing fights.[46] And if it be objected that memories from those distant times cannot now influence our feelings, it must at least be admitted that within the life of the individual a firm foundation is laid for association between pleasure and activity.[47] Independently of all general theories, we must therefore reckon with association as a factor by which the motor element of pleasure is greatly increased. But it seems to us impossible to make the remembrance—conscious or unconscious—of earlier similar states the only ground of the activity which is connected with pleasurable feelings. It is at least far more simple and consistent to explain, with Hamilton and Bain, the activity itself as the physiological condition of pleasure. If any increase of function—whether brought about by chemical, mechanical, or psychical (that is, indirectly mechanical) influences—be considered as a physiological condition of pleasure, and any arrest of function in the same way be considered as a counterpart of pain, then all states of pleasure or pain may be included in one common interpretation. Only it must be remembered that the increase of function can never be measured by any absolute standard. The same stimulus which in one individual calls forth pleasure may in another individual cause pain, and the same bodily activity which we enjoy when in a vigorous state of health may occasion suffering when we are weak or ill. Such variations are evidently conditioned by the varying functional powers of the organs involved. When these powers are reduced, a stimulus, or a movement which usually produces a stimulating effect, may instead call forth depression and pain.