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77. Those who maintain, that the carbonic acid 

 is not directly formed by the union of the oxygen 

 gas of the air with the animal carbon, but that it 

 escapes ready formed from the animal system, ought 

 to point out some other source from whence, in suf- 

 ficient quantity, the oxygen gas can be derived : to 

 tell us at the same time what becomes of the oxyge- 

 nous portion of the air that actually disappears : and 

 why the production of carbonic acid bears always so 

 constant a proportion to the loss of this oxygen gas. 

 To suppose with Spallanzani, that this acid is yield- 

 ed by the process of digestion, because some snails 

 which had been well-fed, furnished more of it than 

 others which had suffered a long abstinence, is by no 

 means proving the point ; for a snail which had 

 long fasted, yielded as much, in one instance, as 

 those which had been recently fed, and, in the other 

 examples, the starved snails fell short only in a small 

 degree. Every animal function, also, is, cateris fia- 

 ribus, carried on best in a state of health and vi- 

 gour, which again depends altogether on a due sup- 

 ply of food : hence, therefore, the debility succeed- 

 ing to abstinence, must afreet the organs of respira- 

 tion, in common with the other organs, and conse- 

 quently their power of acting so completely on the air. 

 Whatever substances, moreover, are received into 

 the animal system, suffer or produce some change : 

 but to suppose, that carbonic acid should be first 

 formed in the stomach, then taken up by the lacteal 

 vessels, and carried through the mass of blood to be 

 again thrown out by the respiratory function, simply 

 as carbonic acid, is not only without proof, but a- 

 gainst all probability. It is also to the quantity of air 



