410 



AX AMEIUCAX TEXT- BOOK OF PHYSIOLOGY. 



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

 from one-sixth to one-tilth 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 C0 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. Nitrogen and argon are omitted because they 

 play no important role in respiration, there being neither absorption nor 

 discharge of either to any noteworthy extent. They take no part, as far as 

 known, beyond that of a mere diluent of the inspired and expired air. 



Inspired air . . 

 Expired air . . 



20.x l 

 1 1 ;.<>:; 



4.78 



< ■( >, 



(Mil 



138 

 4.34 



Water Vapor. 



Variable. 



Saturated. 



Temperature. 



Average about 20° 

 Average, about 30.3° 



Volume 

 (Actual). 



Diminished 



i .i 



to 



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

 cent, richer in 0O 2 ; it is saturated with water vapor, and is of higher tem- 

 perature and of less actual volume. In addition, expired air contains various 

 effete bodies, such as organic matter, hydrogen, marsh-gas, etc. 



The relative quantities of O absorbed and of 0O 2 given off are not constant, 

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



the volume of CO, given offby that of ( ) absorbed/ f~^.= 0.908. Hence, 



O, 4. i 8 



for each volume of <) that is lost 0.908 volume of C0 2 is gained. Various 



conditions affect the quotient (p. 436). 



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 319.'.) to 773.3 grams, or an average of 540 

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

 a daily loss of 526 grams. 



'flie temperature of the expired air varies directly 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 iif 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. Bloeh 1 

 1 ZeUschrifl fur Ohrenheilhtnde, 1888, Bd. xviii. S. 215. 



