91 . 



what power would the carbonic acid that is formed 

 be again given out by that fluid ? No chemical agent 

 either in the air or the water can be imagined equal 

 to the re-attraction of it through the organized struc- 

 ture of the animal : nor is it conceivable, how the 

 blood, by any power of its own, should be able to 

 emit it, independent of such agent. And to suppose, 

 that, by a power of chemical affinity, this gas should 

 enter into the blood, and be afterwards expelled 

 from it, as carbonic acid, by any method analogous 

 to the ordinary animal excretions, is too inconsistent 

 to be entertained for a single moment. 



76. On the grounds, therefore, that the oxygen 

 gas of the air does not obtain admission into the 

 blood-vessels, either by the function of absorption, 

 or by the operation of chemical affinity, we must re- 

 ject the belief of its union with the supposed carbon 

 of the blood, to form the carbonic acid that is pro- 

 duced. Still, however, the gradual disappearance 

 of that gas, and the production of carbonic acid 

 which ensues, justify the conclusion, that in the ani- 

 mal, as well as in the vegetable, kingdom, they ob- 

 serve always a regular and progressive ratio, and 

 are, in fact, proportional to each other, which ad- 

 mits of no other solution than that of their being 

 converted into one another. To effect this conver- 

 sion, however, no other substance but the animal 

 was present, in these experiments, from which the 

 carbon could be derived ; consequently, the acid 

 must be formed by the union of carbon furnished 

 by the animal with the oxygen gas of the air, and 

 this, too, exterior to the vascular structure of the 

 animal. 



