It is thus seen that under normal conditions respiration is effected through the nose, the lips being closed and the oral cavity occluded anteriorly and posteriorly by means of the tongue. The latter completely fills the oral cavity during nasal respiration, its tip being pressed against the upper teeth and the dorsum and edges fitting against the palate and alveolar processes, while the base of the tongue arches upward and is closely applied to the soft palate, so that the oral cavity is hermetically closed and shut off from the pharynx.

The question presents itself, whether the mouth is capable of supplying the functions of the nose in preparing the air for respiration, or whether mouth-breathing is injurious to the organism; and the answer must be that the oral cavity is not in any way adapted to replace the nose in the act of breathing. The width of the oral cavity is such that the air-current encounters no resistance, and consequently its progress is not retarded, as it is in the narrow passages of the nasal cavity, and no time is afforded for purification and saturation. The less abundant vascular supply and the absence of cavernous tissue (the amount of blood in which is regulated by the external temperature, and thus tends to maintain the required degree of temperature in the nose); the absence of an abundant watery secretion in the oral cavity; the nature of the epithelium in the mouth, which is of the squamous variety, and therefore incapable, in contradistinction to the ciliated epithelium in the nose, of removing automatically any deleterious substances in the air-current all these structural differences combine to make the mouth unfit to supply an air-current which would be other than injurious to the organism.

II. Pharynx and Larynx as Respiratory Pathways. -When the air reaches the pharynx and larynx, after passing through the nose, it has undergone the necessary preparatory changes for its entrance into the lungs, and needs no further alteration of any moment. If any particles of dust enter the larynx with the inspired air, they are promptly expelled by the ciliated columnar epithelium. But the pharynx and larynx are nevertheless supplied with a protective apparatus capable of preventing the passage of foreign bodies in either direction-into the postnasal space and the nose, or into the trachea and deeper air-passages; and it is called into activity whenever food is taken, to

guard the air-passages against the invasion of food particles. The oral cavity is completely shut off from the rhinopharynx by the application of the soft palate against the posterior pharyngeal wall, but the larynx is not entirely occluded during deglutition, the bolus of food gliding easily into the esophagus over the arching dorsum of the tongue (which guards the entrance to the larynx), so that the action of the epiglottis in closing the larynx is not absolutely indispensable. If a foreign body, however, does get into the larynx, the glottis immediately closes, -as it does always at the slightest touch,-and the offending particle is expelled by coughing.

DISEASES OF THE LUNGS DUE TO DISTURBANCES OF THE PHYSIOLOGIC FUNCTION OF THE UPPER AIR-PASSAGES.

In returning from this physiologic digression to the discussion of the influence exerted on the respiratory organs by disease of the upper air-passages, I shall adopt a classification in which the first place is accorded to those diseases of the lung that develop in consequence of disturbances of the function of the upper air-passages.

Such disturbances may arise because the respiratory aircurrent can not make its way through the nose, so that mouth-breathing becomes necessary. The obstruction may be situated in the nose or in the postnasal space. Any one of the following conditions may be present, and necessitate mouth-breathing: Hyperplasias and tumors in the nose; structural anomalies in the framework of the nose obstructing the lumen, caused by deviation of the septum, by ridges on its surface, or by abnormal bulging or cystic formations in the muscles; occlusion of the posterior nares by tumors in the postnasal space, and especially by adenoid growths on the vault of the pharynx. The evil effects of mouth-breathing first manifest themselves in the mucous lining of the pharynx and larynx, which becomes dry because the air has not been properly prepared and saturated. Dust particles are deposited first on the mucous membrane of the mouth and oral pharynx-which is covered only with squamous epithelium-and later make their way into the larynx and deeper air-passages. The constant irritation of the dry and unpurified air coming in contact with the mucous membranes of the upper and lower

air-passages gives rise, as we can easily understand, to chronic catarrhal conditions. Thus it is found that mouthbreathers, as represented typically by children in the early stages of enlarged tonsils, are prone to become the subjects of catarrh of the upper air-passages, of recurring pharyngeal and laryngeal catarrh, and of acute bronchial catarrh ; while if the condition continues, they usually develop chronic bronchitis, which can be permanently cured only by restoring nasal respiration.

In this way we can frequently explain the chronic catarrh which is seen almost constantly in children of scrofulous habit, in whom the hypertrophy of the lymphatic elements in the postnasal space is followed by occlusion of the posterior nares. Mouth-breathing is, however, not the only precursor of chronic catarrh in the deep air-passages; the condition frequently develops as a sequel to pathologic alterations in the nose itself, provided they are sufficient to render it unfit to afford the necessary protection to the lungs. In atrophic conditions of the nose, coupled, as they are, with metaplasia of the epithelium, foreign bodies contained in the inspired air cling to the walls of the cavities, and eventually penetrate into the deep air-passages. In examining persons afflicted in this way, whose work obliges them to breathe impure air, a mere inspection of the nose, pharynx, and larynx shows the dust-particles, whether mineral or vegetable, as, for instance, coal-dust and flour, clinging to the mucous surface, and it is easy to understand that these dust-particles may be carried down with the inspiratory blast and settle in the bronchi. Such morbid changes must necessarily favor the development of the various forms of pneumoconiosis, especially anthracosis and chalicosis.

Disturbances of the sensibility and of the reflex activity of the pharynx and larynx have an important bearing on the lungs and bronchi, as they facilitate the development of inspiration pneumonia. If there is anesthesia of the pharynx and larynx, and the cough reflex is diminished, it is easy for particles of food to enter the larynx; and when from anesthesia of the larynx the glottis fails to close, and there is no reflex cough, the offending body readily finds its way into the lower air-passages. Hence an inspiration pneumonia frequently complicates nervous affections, which, like diphtheria, are accompanied with disturbances of sensibility, or, like bulbar disease, with loss of reflexes.

On the other hand, it is worthy of remark that ulcerations and disturbances of mobility in the epiglottis do not, as a rule, interfere with deglutition, and therefore are not followed by inspiration pneumonia. Motor disturbances of the epiglottis are usually mechanical, being due to inflammation and swelling of the member, while ulcerations, which may be so great as to destroy the entire organ, usually result from syphilitic or tuberculous lesions. When either of these conditions is present, we should naturally expect that food particles would penetrate into the airpassages, the entrance to the larynx not being sufficiently occluded by the epiglottis. The fact that it does not happen is proof that the epiglottis is of no great importance as a protection to the larynx, its place being easily filled by the base of the tongue. If, however, the muscles of the tongue are paralyzed or atrophied, as in progressive bulbar paralysis, foreign bodies find no difficulty in entering the deeper air-passages.

DISEASES OF THE LUNGS IN MORBID CONDITIONS OF THE UPPER AIR-PASSAGES.

Diseases of the lungs may owe their origin to direct extension of disease of the upper air-passages to the trachea and bronchi. The causes are the same as those we have referred to in discussing the relations existing between diseases of the upper air-passages, chronic hypertrophic and chronic atrophic catarrh, and suppurative processes in the nose, in its tributary cavities, and in the postnasal space. Chronic bronchitis is the most frequent of the various sequels, and proves very obstinate, especially in cases of chronic suppuration in the tributary cavities of the nose, where the pus trickles down from the nasal pharynx into the deep air-passages and sets up a chronic irritation. The question of the relation between chronic catarrh of the upper and of the deeper air-passages has not received the attention it deserves; it is barely mentioned in the most general terms in connection with bronchitis, and the possibility of emphysema, bronchiectasis or fetid bronchitis being due to such causes is usually ignored. A paper by Sticker,1 in which he establishes a causal relation between atrophy, or dry catarrh of the mucous membranes of nose 1. Arch. f. klin. Med.," vol. LVII.

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and pharynx, and similar atrophic conditions in the trachea, bronchi, lungs, and pleura, is therefore worthy of notice. Genuine ozena, or rhinitis fœtida atrophica, is an atrophic process in the mucous membrane, shared to some extent by the skeleton of the nose, so that the turbinated bones are often entirely destroyed, and the nasal cavity attains enormous dimensions. The atrophy affects the glands and the erectile tissue, partly destroying both structures, but does not extend to the blood-vessels, which, on the contrary, according to recent investigators, become dilated. At the same time the ciliated cylindric epithelium is converted into horny squamous epithelium, giving the mucous membrane a dry, cicatricial appearance, which in the later stages also extends to the pharynx and larynx after the atrophic process has reached these parts. The disease is regularly accompanied by the secretion of a tenacious material, which dries, forms crusts, and gives off a characteristic penetrating fetor. The discharges make their way into the pharynx and larynx, and thence into the deeper air-passages, where they may set up chronic irritative conditions. Sticker has shown that, aside from the fact that diseases of the lungs may be caused by disease of the deeper air-passages secondary to a similar process in the nose and postnasal space, there is a general condition of which the atrophy of the mucous membrane is merely the superficial expression, and this he has called xerosis of the mucous membranes. This condition eventually leads to a wide-spread and more or less complete atrophy of all the mucous membranes in the body, and, as old age comes on, to a progressive increase in the size of the nasal and postnasal cavities, the larynx, the trachea, the bronchi, and, finally, the lungs. In cases of marked atrophy with ozena of the nose and pharynx experience teaches us to expect not only chronic bronchitis, but also emphysema and asthma-like attacks. If such a condition is met with in elderly persons who have all their lives suffered from chronic bronchitis due to ozena, it is readily explained as senile emphysema, or as a secondary emphysema, such as may develop gradually in chronic bronchitis. But how are we to explain such cases of pulmonary emphysema in young persons, barely twenty years old, with all the symptoms-especially dyspnea and cyanosis—which are found only in the severest grades of emphysema?