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TEXT-BOOK OF PHYSIOLOGY 



space between which is filled with water. The center of the box is an air 

 chamber. A thin walled mica box sinks into the water. Posteriorly it is 

 attached to and rotates around an axis, which permits of an elevation or 

 depression of the anterior portion. It is also carefully counterpoised. A 

 light lever attached to the mica box records its movements. The interior 

 of the box communicates by a tube with a large reservoir into which the 

 individual breathes, the object being to prevent a too rapid vitiation of the 

 air. Inspiration causes the lever to descend, expiration to ascend. Previous 

 graduation of the apparatus is necessary to determine the volumes breathed. 

 A graphic record of the volume changes is shown in Fig. 193. 



FIG. 193. DIAGRAM REPRESENTING THE VOLUME CHANGES OF THE THORAX AND LUNGS. 



(Modified front Boruttau.) 



Respiratory Sounds. On applying the ear over the trachea and bronchi 

 there is heard during both inspiration and expiration a well-defined sound, 

 which is loud, harsh, and blowing in character, and which from its situation is 

 known as the bronchial sound. It is especially well heard between the 

 scapulae above the level of the fourth thoracic vertebra. This sound is 

 produced in the larynx, for with its separation from the trachea the sound 

 disappears. The cause of the sound is to be found in the narrowing of the 

 air-passage at the level of the vocal membranes, though the mechanism of 

 its production is uncertain. On applying the ear to almost any portion of 

 the chest-wall, but especially to the infrascapular area, there is heard during 

 both inspiration and expiration a delicate, sighing, rustling sound, which 

 from its supposed seat of origin, the air-vesicles or air-cells, is known as the 

 vesicular sound. This sound is supposed to be due to the sudden expansion 

 of the air-cells during inspiration and to the friction of the air in the alveolar 

 passages. 



THE CHEMISTRY OF RESPIRATION 



The general metabolic process as it takes place in the tissues involves 

 the assimilation of oxygen and the evolution of carbon dioxid. The former 

 is the first, the latter the last, of a series of chemic changes the continuance of 

 which is essential to the maintenance of all life phenomena. A constant 

 supply of oxygen and an equally constant removal of carbon dioxid are 

 necessary conditions for tissue activity. The blood is the medium by which 

 the oxygen is transported from the lungs to the tissues and the carbon dioxid 



