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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



inflow and outflow of about 500 cubic centimeters (30 cubic inches), therefore 

 from one-sixth to one-fifth of the air in the lungs is renewed by each act. 

 Since the respirations occur at so frequent a rate as 16 to 20 per minute, it 

 seems apparent that there must be a rapid loss of O and a gain of CO 2 . This 

 is proven by analyses of inspired and expired air. Inspired air is under 

 normal circumstances atmospheric air, composed of oxygen, nitrogen, argon, and 

 carbon dioxide, with more or less moisture, traces of ammonia and nitric acid, 

 dust and micro-organisms, etc. The essential differences between inspired 

 and expired air are shown by the following table, the figures for the gases 

 being in volumes per cent. Argon constitutes about 1 per cent, of the nitrogen 

 as given in the table : 



Expired air is therefore 4.78 volumes per cent, poorer in O, 4.34 volumes per 

 cent, richer in CO 2 , and 0.15 volume per cent, richer in N; it is saturated 

 with watery vapor, and is of higher temperature and of less actual volume. 

 In addition, expired air contains various effete bodies, such as organic matter 

 (" crowd-poison "), hydrogen, marsh-gas, etc. 



The relative quantities of O absorbed and of CO 2 given off are not constant, 

 and the ratio is known as the respiratory quotient. This is obtained by dividing 



the volume of CO 2 given off by that of O absorbed, 



CO 4 34 



* '' 



= 0.908. Hence, 



for each volume of O that is lost 0.908 volume of CO 2 is gained. Various 

 circumstances affect the quotient (p. 544). The quantity of N given off' is 

 about 7 grams per diem. 



The quantity of watery vapor lost by the lungs varies inversely with the 

 amount contained in the atmosphere and with the volume of air respired. The 

 less the moisture in the atmospheric air and the larger the volume of air 

 respired, the greater the loss. Valentine, in experiments on eight young men, 

 records a daily loss varying from 349.9 to 773.3 grams, or an average of 540 

 grams. Vierordt records a loss of 330 grams, while Aschenbrandt estimates 

 a daily loss of 526 grams. 



The temperature of the expired air varies with the temperature and volume 

 of the inspired air and with the temperature of the body. Valentine and 

 Bruner found that when the temperature of inspired air was from 15 to 20, 

 that of expired air was 37.3 ; when that of inspired air was 6.3, expired 

 air had a temperature of 29.8 ; while when the inspired air was at 41.9, that 

 of expired air was 38.1. When the air is respired through the nose the 

 expired air is warmer than when respiration occurs through the mouth. Bloch l 

 1 Zeitschrift fur Ohrenheilkunde, 1888, vol. xviii. p. 215. 



