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-pulmonic 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. 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 of the lower respiratory passages. 

 The mouth, though frequently serving as an entrance for air, is not primarily 

 a respiratory passage. Both the nasal chambers and the mouth com- 

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

 deglutitory passages cross each other, the former leading directly into the 

 larynx. 



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 capable of being moved, one on the other, by the 

 action of muscles; it is covered externally with fibrous tissue and lined with 

 mucous membrane. The superior laryngeal aperature is triangular in 

 shape, the base being directed upward and slightly forward, the apex 

 downward and backward. The inclination of the laryngeal aperature 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, 



392 



