CHAPTER XV. 



RESPIRATION. 



Respiration is a process by which oxygen is introduced into, and carbon 

 dioxid removed from, the body. The assimilation of the former and the 

 evolution of the latter take place in the tissues as a part of the general 

 process of nutrition. Without a constant supply of oxygen and an equally 

 constant removal of the carbon dioxid, those chemic changes which under- 

 lie and condition all life phenomena could not be maintained. 



The general process of respiration may be considered under the following 

 headings, viz.: 



1. The anatomy and general arrangement of the respiratory apparatus. 



2. The mechanic movements of the thorax by which an interchange of 



atmospheric and intra-pulmonary air is accomplished. 



3. The chemistry of respiration; the changes in composition undergone by 



the air, blood, and tissues. 



4. The nerve mechanism by which the respiratory movements are main- 



tained and coordinated. 



THE RESPIRATORY APPARATUS. 



The respiratory apparatus consists essentially of : 



1. The lungs and the air-passages leading into them: viz., the nasal chambers, 



mouth, pharynx, larynx, and trachea. 



2. The thorax and its associated structures. 



The nasal chambers are the natural entrances for the inspired air. 

 Their complicated structure slightly retards the movement of the air, in 

 consequence of which its temperature and moisture are adjusted to the 

 physiologic conditions for the lower respiratory passages. The mouth, 

 though frequently serving as an entrance for air, is not primarily a respira- 

 tory passage. Both the nasal chambers and the mouth communicate 

 posteriorly with the pharynx, in which the respiratory and the deglutitory 

 passages cross each other, the former leading directly into the larynx. 



The larynx is a complicated mechanism serving the widely different 

 though related functions of respiration and phonation. It consists of a 

 framework of cartilages, articulating one with another, united by ligaments 

 and moved by muscles; it is covered externally with fibrous tissue and lined 

 with mucous membrane. The superior opening of the larynx, the glottis, 

 is triangular in shape, the base being directed upward and forward, the 

 apex downward and backward. The inclination of the glottic opening is 

 almost vertical. 



The cavity of the larynx is partially subdivided by the interposition of 

 the vocal bands into a superior and an inferior portion. The opening, 

 bounded by the vocal bands, is also triangular in shape, though in this case 



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