304 



VETERINARY PHYSIOLOGY 



that at one end of the tube oxygen is constantly being taken 

 up and carbon dioxide constantly given off, a diffusion of the 

 gases in the direction indicated by the arrows will continually 

 go on, and thus a constant supply of oxygen will be conveyed 

 to the bottom of the tube, while carbonic acid will constantly 

 be cleared out. This is exactly the condition in the lungs. 



The lower part of the tube corresponds to the air vesicles 

 the upper part to the air passage in which the air is con- 

 stantly being exchanged by the movement of respiration. 



The mechanism by which the gaseous exchange in the alveoli 

 is carried out is thus a double one. 



IV. Breath Sounds. The air as it passes into and out of the 

 lungs produces sounds, which may be heard on listening over 

 co z o the thorax. The character of the breath 



sounds are of the utmost importance in 

 the diagnosis of diseases of the lungs, and 

 must be studied practically. (Practical 

 Physiology.) 



On listening over the trachea or over the 

 bifurcation of the bronchi behind, a harsh 

 sound, something like the guttural cJi 

 (German ich), may be heard with inspira- 

 tion and expiration. This is called the 

 bronchial sound. 



If the ear be applied over a spot under 

 which a mass of air vesicles lies, a soft 

 sound, somewhat resembling the sound of 

 gentle wind among leaves, may be heard 

 throughout inspiration, and for a third or 

 less of expiration. This is called the vesicular sound. 



When the air vesicles become consolidated by disease, the 

 vesicular sound is lost and the bronchial sound takes its place. 

 The cause of the vesicular character is therefore to be sought in 

 the vesicles, infundibula, or small bronchi. 



The cause of the bronchial sound has been determined by 

 experiments on horses. In the study of the cardiac circulation 

 it was shown that a column of fluid and the same is true of a 

 column of air moving along a tube of uniform calibre, or with 

 the calibre only slowly changing, produces no sound. Any 



I 



FIG. 139. Shows the 

 course of diffusion 

 of Oxygen into, and 

 of Carbon Dioxide 

 out of, the Air 

 Vesicles. 



