intensity of stimulus often at first increases a pleasure, then decreases it, then produces an increasing painfulness, — a series of which we have no counterpart in sensational experience.
14. The differentiation of the typical sensations seems to be related to differences of environmental action upon us. The eye mediates ethereal vibrations. The ear tells of air waves. Heat and cold terminals react to molecular vibrations. Taste probably deals with chemical reactions. But pleasure and pain are not determined by any such special relation to our environment. Heat may be painful or pleasurable; so may cold, so may taste, so may touch, to go no further.
15. The alterations of pleasure-pain phase which are observed in connection with identical stimuli at different times are apparently incompatible with the sensational hypothesis. Hypernormal activity in any special direction often produces pleasure at one moment and pain at another, the change occurring often within narrow time limits. Are we to suppose that under certain conditions the pain-sense organs are affected by a given stimulus and the pleasure organs not, while under some mysterious altered conditions with the same stimulus the pain organs become quiescent and those for pleasure become active? We surely are in a position to ask for some explanation of this mode of stimulation so different from that found with other senses. Again, activities which are uniformly disagreeable when first experienced, if not too extreme or too long continued or too often stimulated, habitually become gradually less disagreeable and finally may be productive of pleasures. This process is commonly described as the 'acquisition of tastes.' The only explanation of these phenomena in terms of the sensational theory would seem to be that pain nerves become separated from activities or cease to act when the latter function, and that pleasure nerves begin to become connected with the same activities. But what has kept these pleasure nerves from atrophy during the long periods they have been inactive? And after the new connection of the activities with pleasure why do not the pain nerves suffer atrophy, as they certainly do not? For we find that a man who has learned to enjoy the taste of olives,
