former and to prompt to the latter, they become properly incorporated into the instincts and habits requisite to promote life and to render its continuance possible and certain. And here, as with sex, we find the strength of the pleasures proportional to the vital importance of their functions. The theory of properly distributed specific nerves explains all this with a clearness that the rival theory gives no suggestion of.
Specific nerves also explain another relationship between our pleasures and the various senses which they accompany. The physical processes of some of our sense organs are more delicate than others, while the senses among themselves display no intensive contrasts relative to those shown between their physical processes. Thus sight waves are far more delicate than sound waves and sound waves than mechanical rubbing, but we cannot distinguish any corresponding scale of psychic intensities between sights, sounds, and touch. On the other hand, as we have just seen above, we do observe a scale of intensities for our pleasures, correspondent to those of the influences causing such in the various sense organs. Sight is the 'clearest' of all the senses, its processes the most delicate, its pleasure sensations, if there be such, the most indistinct and uncertain. On the other hand, the pleasures of sex markedly agree with the physical mode of their production, but contrast with the low objective clearness of the accompanying touch sensations. A scaling of the other senses would show a like law. All this is precisely what we should expect of specific nerves having like nature, wherever located, but subjected to various influences of unlike vigor; and it is the inverse of what should be looked for a priori from the quale standpoint — namely, that the more distinct the sensation, the more distinct should be its pleasure quale.
Most of the facts which we have noted for the separateness of pain sensations speak as well for the independence of pleasure. We said a pain was always a pain; so pleasure is always pleasure. All kinds of sensations are at times so feeble and indistinct that we cannot tell of what kind they are. So with some pleasures. But, so soon as we do recognize the quality at
