RESPIRATION. 



353 



inspiration are to those of expiration in point of time as 5 to 6, 

 while the vesicular sound of inspiration is to that of expiration as 

 o to 1. The cause of vesicular sound, according to one theory, is 

 supposed to arise from the passing of air into and out of the alveoli 

 and infundibula, the friction here generating a sound, aided by the 

 sudden dilatation of the air-vesicles. 



If now the stethoscope is placed over the trachea just above the 

 suprasternal notch, two sounds are heard: one during inspiration, 



the other during expiration. They are 

 not of equal length; the inspiratory is 

 the longer. The quality of both sounds 

 may be described as blowing, tubular, or 

 bronchial. The expiratory part is more 

 intense and frequently of higher pitch. 

 This bronchial sound is produced by air 

 in passing through the chink of the 

 glottis, which is thrown into vibration, 

 and imparts its motion to the columns of 

 air in the trachea and bronchi. 



In practical medicine it is inferred 

 that, when the vesicular murmur is 

 heard over any portion of the lung-tis- 

 sue, this area being properly distended, 

 the lung is in a healthy condition. If, 

 however, the expiratory portion of it be- 

 comes loud and prolonged, it excites 

 inquiry. 



Fig. 123. Spirometer. QUANTITY OF AIR BREATHED. 



The determination of the volume of 



to^refeve h the eC a e ir expSea^ air necessary to the needs of human 



respiration is a problem that has re- 

 ceived much attention. Because of a multitude of circumstances, 

 both external as well as those that are proper to the individual himself, 

 the figures representing the quantity of air that enters the lungs at 

 each inspiration and the quantity that leaves them at each corres- 

 ponding expiration can scarcely have more than an approximate value. 

 Nevertheless, results which sufficiently agree to permit of establish- 

 ing an average of the quantity of air put in circulation during each 

 normal respiratory movement have been arrived at. It is very gen- 

 erally admitted that in an adult and healthy man, each inspiration 



