96 TPIE HORSE IN HEALTH AND DISEASE 



THE CHEMISTRY OF RESPIRATION 



A clue to the chemical changes that take place in the lungs 

 may be had by comparing the composition of inspired and expired 

 air. From a physiologic standpoint the essential constituents 

 of atmospheric air are oxygen and nitrogen. The accompanying 

 table shows the average per cent, of each : 



CO2 



O. and CH4. N. 



Inspired air 21.0 0.0 79 



Expired air 16.5 4.5 79 



Difference 4.5 4.5 6 



It is seen that the respired air loses oxygen and takes on carbon 

 dioxid and methane. The former is largely derived from oxida- 

 tion of the various organic compounds of the body. The latter 

 comes, in most part, from the destruction of cellulose in the intes- 

 tines. 



The amount of oxygen absorbed and other gases given out varies 

 with the size of the animal and the activity of the tissues of the 

 body. In a state of rest a horse of 1100 pounds weight has 

 been found to absorb 5260 liters of oxygen, and give out 5060 liters 

 of carbon dioxid in twenty-four hours. During exercise these 

 amounts are greatly increased. Exposure to cold causes increased 

 oxidation and a corresponding increase in the respiratory ex- 

 change. 



The amount of air breathed by a horse, as determined by King, 

 was found to be 142 cubic feet per hour and about 3400 cubic feet 

 per day. When air contains over 3.3 per cent, of air that has been 

 previously breathed it is considered impure or contaminated. 

 To provide a stabled horse with substantially pure air necessitates 

 an hourly supply of 4296 cubic feet, or more than 100,000 cubic 

 feet each twenty-four hours. 



A reduction in the amount of oxygen in the respired air in a 

 stable is not the only detrimental influence on the health of the 

 animal. The accumulation in the stable of the waste products of 

 the body is of just as much importance. Excreta liberate free 

 ammonia and other volatile substances in large quantities. Ex- 

 periments have shown that the oxygen content of the air can be 

 reduced from about 21 per cent, to as low as 5 per cent, without 

 appreciable detrimental effect, provided the feces and urine are 



