200 ADVANCED PHYSIOLOGY 



THE CHEMISTRY OF RESPIRATION 



Respiration is a process of the absorption and elimination 

 of gases which occurs in all animals. Not all animals, how- 

 ever, have lungs. Fishes have gills for this purpose; some ani- 

 mals (earthworms) can take sufficient amounts of these 

 gases through the skin and need no lungs, gills or any special 

 respiratory organs. Yet these same animals, if not allowed 

 to get rid of carbon dioxid and take in oxygen, shortly 

 die. To understand respiration we must, therefore, study 

 the relation of these gases to the blood. 



Changes in the Air During Breathing. 1. Inhaled air con- 

 tains about twenty per cent of oxygen, while exhaled air con- 

 tains only sixteen per cent, showing that oxygen is extracted 

 from the air while passing through the lungs. 



2. Inhaled air contains no carbon dioxid, or only slight 

 traces of it, while exhaled air contains four per cent. Carbon 

 dioxid is, therefore, added to the air during respiration. 



3. Inhaled air has a temperature which varies with the 

 conditions. On a cold winter day, it may be below zero; on 

 a hot summer day, it may be as high as one hundred degrees; 

 ordinarily it will be in the vicinity of seventy degrees, the 

 temperature at which our rooms are usually kept. Exhaled 

 air is found to be very nearly ninety-eight degrees, the body 

 temperature. Although there is some variation in the tem- 

 perature of exhaled air, it is never much below this point. 

 If the air is inhaled at 70 F., it will evidently be warmed 

 in its passage through the lungs, and the body become 

 cooled in consequence. 



4. The amount of moisture in the inhaled air is variable. 

 On a dry day it is very slight, while on a wet day it is very 

 great; but exhaled air always contains nearly as much moist- 

 ure as it can hold. This can easily be seen by breathing upon 

 a piece of cold glass. The exhaled air, when cooled by the 

 glass, cannot hold as much moisture as when it was warm. 



