CHEMISTRY OF RESPIRATION. 377 



also found in the atmospheric air. Besides these constituents, 

 which are universal, there are many others that may or may not 

 be present as the result of processes of manufacture. 



Expired Air. When the atmospheric air has been breathed its 

 composition is markedly changed in the following particulars : 1. 

 It has gained carbon dioxid, the amount being increased from 0.03 

 or 0.04 part per cent, to 4.38. 2. It has lost oxygen, the 20.96 

 volumes per cent, being reduced to 16.03, or about 5 per cent. It 

 should be noted that the loss of oxygen is greater than can be 

 accounted for by the amount of that gas returned in the carbon 

 dioxid, the difference representing the amount used up in processes 

 of oxidation constantly going on in the body. 3. It has gained 

 watery vapor, the expired air being saturated. The actual amount 

 of vapor which it receives while in the lungs will, of course, vary. 

 If the air when inspired is cool and dry, it will absorb more 

 moisture from the body than if it is moist and warm. The daily 

 loss from this source is about 540 grams. 4. The expired air is, 

 as a rule, warmer than the inspired. Thus in a series of obser- 

 vations it was found that when the inspired air had a temperature 

 of from 15 to 20 C., when expired its temperature was 37.3 

 C. ; when the inspired air was 6.3 C., it was 29.80 C. when 

 expired; and when 41.9 C. at inspiration, it was 38.1 C. at 

 expiration. The inspired air is warmed from 1 to 2 degrees more 

 when taken in by the nose than by the mouth. 5. The actual 

 volume of expired as compared with inspired air is less by about 

 2 per cent. 6. The expired air contains certain volatile organic 

 matters, whose presence is at once recognized by the sense of smell, 

 among them crowd-poison, although chemists have not yet made 

 us acquainted with their exact composition. 



The following table represents the average composition and 

 temperature of inspired and expired air : 



Inspired Air. Expired Air. 



Oxygen 20.96 16.03 



Nitrogen 78.00 78.00 



Argon 1.00 1.00 



Carbon dioxid 0.04 4.38 



Watery vapor variable saturated 



Temperature '. " about 37 C. 



Respiratory Quotient. This is a term employed to express the 

 ratio between the carbon dioxid given off and the oxygen ab- 

 sorbed, and is obtained by dividing the former by the latter i. e., 

 CO 4.34 

 O 4 93 = 0-88, so *^at there is gained 0.88 volume of CO 2 for 



every volume of O absorbed. This ratio is an exceedingly vari- 

 able one, differing in different animals, and even in the same indi- 

 vidual with age, food, temperature of the air, during exercise, etc. 

 There are various reasons which account for these differences. 



