384 SPECIAL PHYSIOLOGY. 



close network; they are composed of small, soft, nucleated, gray, or 

 non-medullated nerve-fibres, having no white medullated fibres amongst 

 them ; their ultimate fibrillae are said, by Schultz and others, to join 

 the rod-like bodies, named the olfactory cells, which are found between 

 the ordinary epithelial cells. Through these cells, which are regarded 

 by Schultz as nervous structures, or bi-polar nerve-cells, the ends of 

 the olfactory nerves are believed to reach the very surface of the mem- 

 brane, in the form of delicate threads, which project between the ordi- 

 nary epithelial cells, and are kept constantly moistened by the secre- 

 tions of the part. 



Of the three regions of the nasal fossae, the upper one alone, which 

 corresponds to the narrow part to which the olfactory nerve is distrib- 

 uted, is the true olfactory region or seat of smell; the middle region, 

 ciliated like the rest of the air-passages, may be regarded as the 

 respiratory part of the nose, which organ, indeed, is placed, for obvious 

 purposes, in the track of the respiratory passages ; the lower region 

 is the common aperture to the two others, and, being nearer the sur- 

 face, is more cutaneous in its character. The region of the sinuses is 

 not directly concerned in smell ; but these cavities may act as reser- 

 voirs for odorous emanations, so as to prolong olfactory impressions ; 

 they chiefly aid, however, in providing moisture for the interior of the 

 fossae. Even the lachrymal secretions, or tears, having performed the 

 office of moistening the eyeballs, pass, through the canal already men- 

 tioned, into the nasal fossae, and serve a similar purpose. 



Odors. 



It is not yet known why certain bodies are odorous, and others not. 

 As regards the physical condition proper to odorous bodies, it is cer- 

 tain, however, that most, if not all, are volatile, or else actually aeri- 

 form or gaseous, at ordinary temperatures ; but all volatile bodies, or 

 bodies capable of assuming the form of vapor, are not necessarily 

 odorous, as, for example, water. Certain bodies, or fine particles of 

 them, conveyed mechanically through the air to the nose, may cause 

 smell, either on being dissolved in the fluids of the nose, or by being 

 previously volatilized, or by giving off odorous effluvia, which are then 

 dissolved in the fluids of the nose. 



The chemical constitution of odorous bodies, offers no certain expla- 

 nation of this peculiar quality. For example, some elementary sub- 

 stances, as chlorine and copper, produce the sensation of smell, whilst 

 others, as nitrogen and silver, do not ; again, of allied chemical sub- 

 stances, such as the salts of copper and silver, the former are odorous, 

 whilst the latter are inodorous. As a rule, imperfectly oxidized sub- 

 stances, or those which have a tendency to further oxidation, such as 

 essential oils, have a strong odor ; but even a most perfectly oxidized 

 body, such as carbonic acid, possesses an odor, though this may rather 

 depend upon its irritating property, when it is of a certain strength ; 

 for, if diluted, it has no smell. Many perfectly oxidized bodies do not 

 smell at all, as, for example, water ; some smell very slightly, as 

 sulphuric, phosphoric, and chloric acids. Hyper-oxygenated bodies, 



