the entrance and exit of air in breathing. The olfactory nerve-ends ramify over a much smaller area in man than in most of the lower animals, and the sense of smell is correspondingly less highly developed and of smaller importance in man. The olfactory area in the human being is limited to the surface of the septum and the external wall, above the middle turbinal and anterior to the sphenoid bone. The current of air bearing odoriferous particles or vapor enters the narrow olfactory chink during ordinary inspiration, but it is directed thither more forcibly during sniffling,—short, abruptly ending inspirations, which creates eddies in the intranasal aircurrent and thus favors diffusion. The expired air does not enter the olfactory fissure on account of the configuration of the posterior choanæ. For this reason odors arising from the presence of decomposed secretions in the throat and nose are not perceptible to the patient himself. Inflammatory swelling leads readily to occlusion of the olfactory chink, thereby abolishing the sense of smell temporarily. To what extent the nerves of smell and their terminal epithelia suffer permanently in various nasal diseases has never been determined.

By reason of the shape of the vestibule, the current of air during inspiration is directed somewhat upward, and describes a curved path mainly through the middle. meatus to the posterior choanæ. Eddies are produced in the air-current on account of the various irregularities of the intranasal surfaces, and this rotary motion favors permeation of all recesses by the moving air. In its passage through the nose the air undergoes three changes: It is warmed nearly to the body-temperature, is saturated with aqueous vapor, and is partially freed from dust. This influence upon the inspired air is due to the large expanse of nasal surface and its high degree of vascularity. The absolute amount of warmth imparted to the air depends, of course, upon its previous temperature. The quantity of moisture lost by the nose varies likewise with the atmospheric conditions. The saturation of the inspired

relatively dry air of a winter's day requires about 30 grams of water an hour. This high figure would naturally be much reduced on warm days or in moist weather. The deposition of dust is favored, no doubt, by the vestibular hairs, but depends mostly on the convolutions of the moist surface over which it passes. This clearing of the air is not, however, absolute, and the filtering mechanism proves insufficient when the air is unusually dusty. The deposited dust containing living germs is expelled from the nose by the pushing motion of the epithelial cilia, which wave in the direction toward the anterior nares. Experimentation has shown that in spite of the microscopic dimensions, the energy of the ciliary motion is quite considerable, on account of the rapidity of the vibrations. Various observers have found that the internasal surfaces harbor remarkably few bacteria, although every breath of air deposits its living dust. It has been claimed, but has not been definitely proved, that the nasal mucus possesses some bactericidal properties. The surface, to the depth of the cilia on the epithelial cells, is continuously bathed by a layer of mucus, but during health there is never sufficient secretion to flow along or accumulate on the surface except momentarily in response to irritation. This statement applies equally to the pharyngeal lining.

Narrowness of one side of the nose does not interfere with ordinary breathing if compensated for by sufficient width of the other side. It makes the subject, however, short-winded on exertion. But if both nasal passages are insufficient, a reflex mechanism enforces opening of the mouth and mouth-breathing results. In its passage through the mouth the air is not warmed, moistened, nor clarified to the same extent as occurs in nasal breathing. Although it cannot be said that cool, relatively dry or dusty air is directly a cause of disease of the lower air-passages, it undoubtedly exercises an unfavorable effect that may aid other disease-producing influences. In nurslings the mechanism of mouth

breathing is not yet fully established, and hence nasal obstruction is more distressing to them, especially during nursing.

The soft palate acts as a triple valve between nose, pharynx, and mouth. When its muscles are at rest there is free communication between these three spaces. During the act of swallowing-likewise gagging and retching—the nasal part of the pharynx is shut off from the lower region. The palate is stretched horizontally and is tense, the posterior pillars are changed into projecting septa applied against the posterior wall, while the constrictor muscles of the pharynx narrow its caliber and cause its posterior wall to touch the edge of the palate. When this mechanism is viewed from above through the nasal passage, widened by any destructive disease, the pharyngeal wall appears constricted in a ridge meeting the elevated palate. This protrusion, due to the action of the constrictor muscles, is known as Passavant's ridge. Incidentally the levator and tensor palati muscles cause the Eustachian orifice to gape during their contraction in swallowing. When the palatal muscles are paralyzed, as in postdiphtheritic paralysis, the closure of the nasopharynx is incomplete and food and fluids find their way into the nose. If nasal breathing is to continue while the mouth is open, the air is kept out of the mouth by elevation of the base of the tongue, while slight tension of the muscular fibers in the anterior faucial pillars pulls the pendant palate against the tongue.

During speech the palate is in a variable state of activity. Pure vowels are produced only when the air passes through the mouth and the palate is partially raised. If a part of the air passes into the nose, the vowel has a nasal twang. The most pronounced nasal sound, "ng," occurs during absolute relaxation of the palate. The position of the palate varies with the different consonants. A very sensitive test to detect the passage of air through the nose during intonation is

furnished by a cold mirror held in front of the nostril, upon which the expired air will deposit its moisture.

II. The nasal membrane is very sensitive to touch, although deep incisions produce only moderate pain. The nasal sensitiveness resists anesthetics to such an extent that tickling of the inside of the nose with a feather is sometimes of service in impending failure of respiration during narcosis. Nasal irritation, mechanical or chemical, results in sneezing and the free flow of a thin, mucous secretion. The surface of the pharynx is less acutely sensitive than the nasal lining, and its mechanical irritation distresses mainly by reason of the reflex retching movements that it calls forth. Mucous secretion from the pharynx, brought on by irritation, is more viscid than the nasal fluid.

CHAPTER II.

GENERAL ETIOLOGY AND HYGIENE OF NASAL AND PHARYNGEAL DISEASES.

12. Origin of Nasal and Pharyngeal Diseases.— Most nasal and pharyngeal affections are of inflammatory origin, being due either to an acute or a chronic inflammatory lesion or to its consequences. Acute coryza, either simple or as part of some infection (influenza, measles), and the residual inflammatory processes that may persist afterward, as well as hypertrophies thus produced, the involvement of the accessory cavities in the course of a coryza or as part of some general affection, and the various forms of inflammation and enlargement of the pharyngeal lymphatic tissue are responsible for most of the complaints referred to the nose and throat. The parasites giving rise to these infections have been only partly identified. The microbe of common coryza has as yet escaped detection, although the history of the disease leaves no reasonable doubt that it is of microbic origin, while its frequency indicates the universal distribution of the virus. It has, likewise, not been fully established to what extent secondary infection with the various familiar pathogenic microbes is responsible for the prolongation of a coryza. In affections of the nasal sinuses the various forms of pyogenic bacteria-staphylococci, streptococci, pneumococci, diphtheria bacilli, colibacilli, and others have been found. Tonsillitis is due mostly to streptococci, occasionally to other forms. A limited rôle is played by specific infection in the nose and pharynx by the diphtheria bacillus, the bacillus tuberculosis, and the virus of syphilis.

13. "Colds."—Of equal, if not of greater, clinical im