Odor

ODOR. For the olfactory organ, the adequate stimuli are chemical substances which, in negligible amounts (e.g., in one liter of air - 0.00000004 mg of mercaptan) in vaporous or liquid form, or in the form of a suspension of minute solid particles, irritate the olfactory epithelium of the olfactory region. Most authors believe that odoriferous substances dissolve in the secretion of the mucous membrane before reaching the olfactory hairs. Inadequate stimulation also produces a sensation, but to a significantly lesser extent than for other sense organs (electricity, MgSO₄, KMnO₄, palmitic acid, nitrotoluidine, antipyrine). By means of olfactometry and odorimetry, it is possible to determine the sensitivity to one and the same odor in different individuals, or to different odors in the same individual. Zwaardemaker's olfactometer consists of a graduated glass tube, which is curved at the top end so that it can be inserted into the nostril. A cylinder made of a porous substance is slipped over its other end, which can be easily moved along the tube. The porous substance is impregnated with an odoriferous liquid, the evaporation of which into the surrounding air is prevented by a glass case. Sliding the cylinder reduces the area of the odoriferous surface. Certain poisons, e.g., strychnine, cocaine (initially!), increase the sensitivity of the receptor apparatus to odors (hyperosmia), while others, such as morphine, atropine, daturine, decrease it (hyposmia). In this case, a central action is apparently taking place. Cocaine (locally) suppresses sensitivity. When classifying odors, which does not yet have a sufficient scientific basis, it must be borne in mind that many substances, as E. v. Skramlik has shown, simultaneously irritate both the taste endings and the endings of the trigeminal nerve. A. v. Haller distinguished pleasant and foul odors, and between them average, indifferent ones. Zwaardemaker, supplementing Linnaeus's classification, gives the following nine classes of odors: 1) ethereal, 2) aromatic (camphoraceous, spicy, bitter almond, lemon), 3) balsamic, 4) ambro-musky, 5) garlic, 6) burnt, 7) caprylic, 8) obnoxious (narcotic, bug odor), 9) nauseating (cadaveric, fecal). Transitions exist between them. Henning distinguishes 6 basic odors: 1) spicy (pepper, ginger), 2) floral, or fragrant (jasmine oil), 3) fruity (apple ether), 4) resinous, or balsamic, 5) putrid (hydrogen sulfide), 6) burnt odor. Henning systematically places these basic odors in the corners of a triangular prism, placing all transitional and mixed odors between them. Skramlik believes that there are only about 50 pure basic odoriferous substances. The relationship between the chemical structure of an odoriferous substance and the sensation has been established within certain limits only for fatty acids and alcohols. The phenomena of fatigue of the peripheral apparatus in relation to certain odors, analogous to the fatigue of hearing or vision, suggest that there is apparently some differentiation regarding the specialization of peripheral receptors for specific odors. An odor emanating from a patient or from their individual secretions often has the significance of a diagnostic symptom. It is known, for example, that patients with diabetic acidosis emit the odor of sweet apples, uremic patients smell of urea, and those with severe tuberculosis smell like dead mice. Excrement in dyspepsias often emits putrid, sour, and similar odors. Vomitus in supersecretion (see Stomach) has a sour odor, and in gastric stasis, vomitus emits the rancid odor of butyric acid fermentation. Measures to combat bad odors - see Deodorization.