too small a secretion has a disastrous effect on the sense-epithelium. It seems that the tiny hairs of the rod-cells refuse to do their work if they become dry. The action of all the mucous glands of the nose may be increased by injecting strychnine, and decreased by injecting atropin into the membranes, Too much atropin, however, produces irritation and a flow of tears.
Hyperosmia may also be respiratory,—due to certain asymmetries of the skeleton or to anzemia of the respiratory membrane,—or toxic, or nervous, In hysterical subjects, hyperosmia is common. Aneemia of the respiratory membrane may be produced by smelling such substances as cocoa-butter, or cedar-wood, which rather powerfully affect the trigeminus.
The two forms of anosmia, which vary in the same subject from day to day, are respiratory anosmia from obstruction of the nasal passages by mucus, and nervous anosmia from exhaustion. It is possible at any time easily to discover whether the nasal passages are obstructed or not, The test can be made by exhaling on a concave metal mirror held at the level of the mouth, The clouds of condensed vapor give the true shape of transverse sections of the breathing-cones. They are divided from each other, and if the nasal passages are in a normal condition, they are symmetrical, and broader than they are long. As they pass away, they should each divide into an anteromedial and a postero-lateral division of about the same size. As divided, the spots should still be roughly symmetrical, The division is due to the projection of the “triangular cartilage” and the lower turbinal bone from the side wall of the nose. This division of the air current occurs in all mammals.[1] Pathological alterations in the mucous membrane of the nose and asymmetry of the nasal skeleton may alter the size and shape of these divisions, but rarely prevent them from appearing. The antero-metial division alone represents the current of air which passes above the lower turbinal bone. The form and position of the field of smell in an ordinary inspiration, thereore, corresponds roughly with this division, and would do so exactly if it were not for the slight difference in the course of the currents of inspired and expired air.[2]
The influence of exhaustion is more insidious. It varies from subject to subject, from substance to substance, and from one intensity of a substance and one general condition of a subject to another, so that numerical corrections are out of the question. Fortunately or unfortunately, the effects of adhesion and exhaustion are for the most part opposite. This
