COMPOSITION OF EXPIRED AIR. 



231 



With every increase of about 186 meters in elevation above the 

 surface of the earth, the temperature (irregularly, it is true) falls i C. 



Above a level of 4000 meters the cold increases in greater proportion; at a 

 level of 7000 meters the most severe degree of cold prevails without variation, 

 being the same at all seasons. 



COMPOSITION OF EXPIRED AIR. 



The expired air is rich in carbon dioxid, of which it contains on an 

 average 4.38 per cent, by volume (from 3.3 to 5.5 per cent.) during 

 quiet respiration. The amount of carbon dioxid is, therefore, more than 

 100 times greater than in the atmosphere. 



The expired air contains less oxygen (on an average 4.782 per cent, 

 less by volume) than inspired, atmospheric air, 

 namely, only 16.033 per cent, by volume. A 



Hence, during respiration there is more oxygen 

 taken into the body from the air than there is carbon 

 dioxid expelled; so that the volume of the expired 

 air is from one-fiftieth to one-fortieth less than the 

 volume of inspired air (under the same conditions of 

 temperature, humidity, and pressure). This relation 

 of the expired carbon dioxid to the inspired oxygen 

 (4.38 : 4.782) is termed the respiratory quotient: 



= 4.?&) = 0-916- 



A small excess of nitrogen is admixed with the 

 expired air. It has been found that not all of the 

 nitrogen taken up with the food appears again in the 

 excretions (urine and feces). 



The expired air during quiet respiration is satur- 

 ated with aqueous vapor. It is, therefore, evident 

 that, by reason of the changes in the amount of water 

 contained in the air, a varying quantity of water must 

 be excreted by the body through the lungs. With 

 rapid respirations Moleschott observed the percentage 

 of aqueous vapor to fall. The surrounding tempera- 

 ture also has an influence on the amount of water given 

 off: the minimum occurs at 15 C., while below this 

 point the amount increases moderately, and above the 

 quantity rises rapidly. 



The expired air possesses a considerable degree of 

 heat (on an average 36.3 C.), which at moderate ex- 

 ternal temperatures approaches quite closely that of 

 the body; but even with extreme variations of the 

 surrounding temperature the degree of heat main- 

 tains itself within the same limits. 



Valentin and Brunner employed the instrument repre- 

 sented in Fig. 89 to determine the temperature of the expired 

 air. It consists of a glass tube A A, with a mouth-piece 

 and an inserted, delicate thermometer C. Inspiration is made through the 

 nose, and the air is slowly expelled through the mouth-piece into the tube. 

 Temperature of the Air. Temperature of the Expired Air. 



-6.3 C. +29-8 C. 



+ i 7 -i 9 C + 36.2-37 C. 



+ 44 C. 



FIG. 89. Apparatus 

 for Measuring 

 the Temperature 

 of the Expired 

 Air. 



