Yet in spite of the tens of thousands of sensations, and in spite of the extraordinary sensitivity of the cells, we often read that in man the sense of smell is degenerating! Of this there is not one particle of evidence. We could not, truly, live by smell, as dogs do; but then men have never been dogs; and even so there are cases on record—among the Botocudos of Brazil and the aboriginal tribes of the Malay peninsula—of savage hunters who track their game by scent. There is no atom of evidence that, since man was man, his sense of smell has degenerated. It is true, on the other hand, that =the sense of smell has fallen into disuse=. The reason is that smell is essentially a ground sense, as you may convince yourself any summer day that you lie out on the grass, or any time that you are willing to spend a few minutes on a dining-room floor; birds in general have a very obtuse sense of smell, and many of them perhaps lack sensations of smell altogether. When, then, mankind assumed the upright position, and the nostrils were lifted several feet above the surface of the ground, the sense was removed from its normal environment, and fell into disuse; sight and hearing took its place. But it may still be used. The late Sir Francis Galton, a cousin of Darwin’s, once made an essay, for instance, at an =arithmetic by smell=; peppermint stood for one, camphor for two, carbolic acid for three, and so on. “There was not the slightest difficulty in banishing all visual and auditory images from the mind, leaving nothing in consciousness besides real or imaginary scents. In this way I convinced myself of the possibility of doing sums in simple addition with considerable speed and accuracy solely by means of imaginary scents. Subtraction succeeded as well as addition.” Needless to say, it is not worth our while to do this sort of work; the very fact that odours have no settled system of names, like cold or pain, red or blue, shows that they have not been utilized in human life. It is fair to add, also, that sight and hearing are better suited than smell to our everyday needs; for smells very soon fade out and disappear; indeed, if they did not, the work of garbage collectors or of medical students in the dissecting room would be permanently disagreeable. § 12. =Sensations from the Ear.=—Sensations of hearing fall into two great groups, tones and noises. When we are speaking of =tones=, we naturally think of the keyboard of a piano. The piano tones are, in reality, not simple tones or sensations but compound tones; and we are able, after a little practice, to break up a compound tone into its simple constituents. You may get a fair notion of a really simple tone by blowing gently across the mouth of an empty bottle. The tone is dull and hollow, as compared with the bright solidity of a piano tone, but it has also a pleasant mellowness. With these two aids, the bottle tone and the piano keyboard, we may approach our study of tonal sensations.