The nerves of the nose are the first pair or olfactory, which are specially connected with the sense of smell; branehes of the fifth pair, which confer ordinary sensibility on its skin and mucous membrane; and motor filanient:Z, from the facial nerves to the nasal muscles. The olfactory nerve on each side is connected with the inferior sur face of the brain by an external, a middle, and an internal root, which unite and form a flat band (or. more correctly, a prism), which, on reaching the erihriform plate of the ethmoid hone, expands into an oblong mass of grayish white substance, the olfactory bulb. From the lower surface of this bulb are given off the olfactory filaments, fifteen or twenty in number, which pass through the cribriform foramina, and are distributed to the mucous membrane of the olfactory region. The branches of the fifth pair (or trifacial) given to the nose are the nasal nerve (derived from the ophthalmic division), which supplies the skin and mucous membrane in the vicinity of the nostrils, and the naso palatine nerve (derived from Meckers ganglion, which is connected with the superior maxillary division), which supplies the mucous membrane on the spongy bones and on the septum. What ever may lie the nature of the odorous matter, it is necessaiT that it should be transmitted by a respiratory current through the nostrils to the true olfactory region. and dissolved or suspended in the fluid with which the olfactory membrane is normally covered. The proper condition of this fluid is one of the essential conditions of the perception of odors. If the membrane is too
dry, or if there is an inordinate excretion of fluid from its surface (both of which conditions occur in catarrh or cold in the head), smell is impaired or lost, in consequence of the necessary penetration of the stimulating odor to the nervous filaments being prevented.
It has been observed that when the nostrils are filled with rose water or eau de Cologne, no odor is perceived, and simply filling the nostrils with distilled water suspends for a time the sense of smell. lf, on the other hand, the scent be dissolved in 'normal saline solution,' which closely resembles the natural secretion, the odor is perceived.
The sense of taste is often confused with that of smell. We speak of 'tasting' an odoriferous substance, step as all 0111011, or a savory dish. or a wine, when in reality we perceive it through the olfactory nerves. This is proved by the fact that the taste for these substances is lost when the smell becomes impaired.
The acuteness of the sense of smell is far greater in many of the lower animals (dogs, for example) than in man. and they employ it in guiding them to their food, in warning them of approaching danger. and for other purposes. To civilized men the utility of this sense is compara tively small; hut it is oceasionally much in creased when other senses are deficient. Among ninny savage tribes the sense is almost as acute as in many of the lower mammals. See Nos