THE RESPIRATORY EXCHANGE 485 



The expired air is saturated with moisture at a temperature 

 between 36 and 37, to which it has been raised during inspiration, 

 and in this way a considerable quantity of water and heat are 

 extracted from the body. It has been calculated that an adult 

 man may thus lose in twenty-four hours as much as 450 grm. 

 of water under ordinary conditions of external temperature and 

 moisture. 



There is a decrease of about 1/50 in the volume of the expired 

 air as compared with the inspired air, when both are measured 

 at and 760 mm. ; the deficit is due to the absorption of a small 

 quantity of oxygen, which does not reappear in combination with 

 carbon as carbon dioxide, but passes out of the body in other 

 products of oxidation. The increased proportion of nitrogen in 

 the expired air must be taken into account when the respiratory 

 quotient is calculated from volumetric analyses ; thus for every 

 100 c.c. of expired air the slightly larger volume of inspired air 

 contained the following volume of oxygen : 



O _ 20*93 x Nitrogen of expired air 

 79-07 



The respiratory quotient, therefore, in a case in which'' the 

 percentages of nitrogen, oxygen, and carbon dioxide are 81, 16*44, 

 and 4, would be correctly calculated as follows : 



Oxygen of inspired air = 70^7 = 21 '44. 



Oxygen absorbed = 21-44 - 16-44 = 5'00 cc. 



C0 9 4 

 Respiratory quotient -^ 



There is no evidence of an active absorption or discharge of 

 nitrogen by the lungs ; the older results which supported such 

 a process or processes appear to have been errors of experiment. 

 It is possible that small quantities of nitrogen may be formed 

 in the alimentary canal and may be directly discharged by the 

 bowel or indirectly by the lungs ; the quantity, however, would 

 appear, from experiments directed to this point, to be negligible. 

 Small quantities of hydrogen and marsh-gas are frequently found 

 in expired air ; the gases are formed during fermentation in the 

 alimentary canal, and are absorbed by the blood and discharged 

 by the lungs. In the case of ruminants a considerable quantity 

 of these gases is present in expired air. 



