SMELL

This sense resides in the mucous or pituitary membrane which lines the nostrils, and the surface of which is more or le convoluted or extended in various orders of animals. In the human subject this membrane is highly vascular, and largely supplied, especially in its upper parts, with nervous filaments, or ramifications of the olfactory trunk, which has its origin, by three distinct roots, from the posterior, inferior, and internal parts of the anterior lobe of the brain, and proceeding towards the perforated plate of the ethmoid bone, divides into the small threads just mentioned. The physiology of odours is a curious and intricate subject, requiring much more experimental investigation than it has hitherto received. The air is the great vehicle by which their various influences are transmitted in the act of inspiring to the olfactory surfaces, and for the diffusion of most odours a certain degree of humidity in the air appears absolutely e ential. There is scarcely any sense the degree of perfection of which varies so much in different individuals as that of smell, some being painfully alive to those odorous influences which are not even perceived by others. An obtusene of this sense is also very frequent, and its almost entire absence by no means uncommon; this is especially the case in certain catarrhal complaints, and in some other affections of the lining membrane of the nose. [s. 1137]