14 On the hijiuence of Air 



of oxygen gas, it will not be necessary to pass in review, 

 as it has already been a subject of so general discussion, 

 and as we have already asserted, that animal heat can 

 arise only from animal action. 



The oxygen is the only portion of the atmosphere 

 which undergoes any change in its chemical properties 

 in respiration. The experiments of Lavoisier prove, 

 that four-fifths of the oxygen which disappears in respi- 

 ration are consumed in the formation of carbonic acid 

 gas, a combination taking place between the oxygen of 

 the atmosphere and the carbon of the blood. The re- 

 maining one-fifth is either, he supposes, absorbed by 

 the blood, or is expended in the formation of water by 

 combining with the hydrogen of the blood ; to which 

 latter opinion we confess ourselves inclined, for die al. 

 teration of the colour of the arterial blood, which has 

 been regarded by Crawford and his followers as a direct 

 proof of the absorption of oxygen, may easily be ac- 

 counted for by an immediate alteration of the consti- 

 tuents of the blood upon its entrance into the lungs by 

 the evolution of its carbon and hydrogen ; for the colour 

 of a body always varies with the alterations of its chemi- 

 cal properties. To this opinion, Seguin, in his Me- 

 moirs on Caloric, in the Annals of Chemistry, seems 

 inclined. 



Having seen in what manner all the oxygen is dis- 

 posed of, let us now examine the modus operandi, by 

 which carbon, hydrogen, and caloric are evolved, the 

 various combinations produced, and the manner in 

 which the functions of this organ of vitality are preserved 



