Those who have made a thorough study of the subject claim that there is a peculiar odor belonging to every class of living beings, and each is subdivided so that each order, family, species, race, and variety is distinct. Furthermore every individual is distinct from the rest of his kind in the odor given off so profusely and unconsciously in most instances. Horses seem to be somewhat less keen than dogs in noting odors, for a horse which is accustomed to but one groom and will not consent to attendance from another may sometimes be deceived by having the new groom dress himself in the clothes of his predecessor. Insects possess this sense to such a degree that flies have been the means of locating a dead rat under a floor by their settling over the body in large numbers, although there was no chance for them to reach it. Just where the organs of smell are in insects has been disputed among scientists. Sir John Lubbock is inclined to the opinion that they are located in the antennæ and palpi, though some contend that insects smell as the air is taken in at the spiracles or breathing-holes which are scattered over their bodies. That fish have this sense to some extent is attested by fishermen who use essential oils upon their bait and secure readier attention from the inhabitants of the water. But fish seem to be less capable of smell than even the reptiles upon land who are not considered at all remarkable in this respect. To make up in some sort for this deficiency there are some kinds of fish which have four nostrils while all other animals that smell at all seem content with but two as a rule. Only those animals having a backbone are equipped with noses that are unquestionably adapted to smelling, but insects, crabs, and mollusks perceive odors to a limited extent. Some of them are readily deceived by odors similar to those they seek. Lubbock calls attention to the fact that the carrion fly will deposit its eggs on any plant that has a smell similar to that of tainted flesh. We are unable to say just what the nature of a smelling substance is which makes it so perceptible to our olfactory organs. Many things, both organic and inorganic, have the power to affect us in a way which cannot be perceived by the organs of taste nor touch. The upper third of the interior of the human nose has the sole function of recognizing them. We have almost no names for the various smells, but they are as distinct as day and night and arouse within us the most intense feelings.