In concluding this chapter we need to remember that the contact senses make up the court of last resort; by the time anything comes close enough to the body to act upon any of them it is so close that the effect in guiding the muscles must be immediate; there is no time for deliberation; whatever the muscles are going to do in response to information thus obtained must be done at once. Later we shall see how this affects our whole bodily make-up.
CHAPTER IX
SENSATION—DISTANCE SENSES
THE three senses that give us information of what is happening beyond the surface of our bodies are smell, hearing, and sight. Since smell is closely related to taste, which was talked about in the last chapter, we shall take it up first. Smell is like taste in that it is aroused by chemical substances, but to be smelled these must be in gaseous form, not dissolved in water, as for taste. The organ for smell is in the upper part of the nasal chamber. There are really two of them, one in each nostril. They are made up simply of little patches of mucous membrane, as the membrane that lines the nose is called, in which are many of the particular kind of cells that are affected by odors. An interesting thing about these patches is that they are not in the part of the nostrils through which the main current of air sweeps in breathing, but in a little pocket off this main channel. If air containing an odorous substance is breathed in or out, a little of it works its way into the side pocket and is smelled. If we wish to get more of the odor we do it by sniffing, which is changing the shape of the nostrils to throw the air current more directly against the smell organs.
These organs are amazingly sensitive. It is hard to appreciate the minuteness of the amounts of material that can be smelled. Especially is this true of those animals that have a really keen sense of
