THE KESPIRATION 



299 



i.e. about 4 per cent, of oxygen is taken from the air, and 

 about 4 per cent, of carbon dioxide is added to it. In man 

 the amount of carbon dioxide given off is smaller than the 

 amount of oxygen taken up. The proportion between the 



"Q + k is called the Respiratory Quotient, and it is 



thus less than unity usually about '8 to *9 that is, for 



every five volumes of oxygen taken up only four volumes are 



given off in carbon dioxide, the 



remainder being combined with 



hydrogen to form water. The 



various factors modifying this 



quotient will be considered while 



dealing with the extent of the 



respiratory changes. 



FIG. 139. Shows the Composition 

 of Inspired and of Expired Air. 



Expired air usually contains more water than inspired air. 

 It is always saturated with watery vapour. 



Expired air also contains small amounts of organic matter, 

 which give it its offensive odour. These may possibly be to 

 a small extent formed in the lungs, but are to a greater 

 extent produced by putrefactive change in the mouth and 

 nose. It is probable that the accumulation of these products 

 in the air is one of the great causes of the injurious effect of 

 the " foul air " in overcrowded spaces. 



Expired air is usually warmer than inspired air, because 

 usually the body is warmer than the surrounding atmosphere. 

 When, however, the temperature of the air is higher than 

 that of the body, the expired air is cooler than the inspired. 



This is illustrated by the figures of an experiment 



Temperature of Inspired Air. 



6-3 C. 



17-19 C. 



41 C. 



44 C. 



Temperature of Expired Air. 



30 C. 

 37 C. 



38 C. 

 38-5 C. 



II. Effect of Respiration on the Blood. To understand 

 these changes in the air we must refer to the changes in the 

 gases of the blood in passing through the lungs (p. 199). 

 Analyses show that the blood going to the lungs is poorer in 

 oxygen and richer in carbon dioxide than the blood coming 



