151 



if it be shewn that the volume of that gas which is 

 lost, actually exceeds that of the .carbonic acid 

 which is formed. , Now, this has been amply done 

 In the experiments (118.) already given: and, in- 

 deed, the excess of oxygen lost, was so apparent 

 and so constant, as to lead Lavoisier, and others 

 after him, to conclude, that it was employed to form 

 a part of the water expelled from the lungs, by uni- 

 ting with hydrogen supposed to reside in the blood, 

 just as water and carbonic acid are formed by the 

 combustion of wax and many other substances. It 

 is, moreover, incumbent on those who hold this opi- 

 nion concerning the production of carbonic acid, to 

 find out some adequate source from whence the oxy- 

 gen gas, forming the expired carbonic acid, can be 

 derived ; to explain to us, at the same time, what 

 becomes of the inspired oxygen gas which actually 

 disappears ; and why the acid produced bears always 

 so constant a proportion to the disappearance of that 

 gas. 



122. Taking for granted, then, that the carbonic 

 acid expired, is formed by the union of the inspired 

 oxygen gas with carbon furnished by the animal 

 system, and that the gas lost exceeds in volume the 

 quantity of acid produced, we proceed next to in- 

 vestigate the amount of this difference and its cause. 

 From the experiments of Doctors Priestley and 

 Crawford (S3.), it appears, that when animals are 

 confined in air inverted over mercury till they die, 

 little or no diminution of the bulk of gas takes 

 place: those of M. Lavoisier, however, furnish a 

 different result. He confined a guinea pig in a jar, 

 containing 248 cubic inches of gas, consisting prin- 



K4 * 



