93 



changed, and not to that of food taken in, that this 

 acid bears a proportion ; and, provided living action 

 be equally well maintained, as much air seems to be 

 required by an animal when he abstains from food 

 as when he takes it, and as much carbonic acid to 

 be produced. In as much, however, as a long ab- 

 stinence from food, debilitates the system, and af- 

 fects the production of carbon, in so much will it di- 

 minish the quantity of carbonic acid, which the ani- 

 mal is accustomed to form. 



78. But the quantity of this acid, when formed 

 by the respiration of a given volume of air, does not 

 seem to exert any noxious operation on the animal 

 powers ; for Spallanzani found, that animals placed 

 in a given bulk of air, did not live longer when the 

 carbonic acid was abstracted by an alkaline solution 

 as soon as formed, than when it was suffered to re- 

 main * ; and, in all our experiments, where the car- 

 bonic acid was allowed to remain, the death of the 

 animals seems to have arisen, not from the over-pro- 

 portion of that acid, but from the diminished quan- 

 tity, or total absence, of the oxygen gas. Since, in- 

 deed, air is necessary to the continuance of living 

 action in all animals, and its nitrogenous portion ap- 

 pears to suffer no alteration, this necessity must arise 

 from its containing oxygen gas, and from the requi- 

 site changes which, in respiration, that gas is made 

 to undergo. When, therefore, the greater part, or 

 the whole of the oxygen gas of the air is so chan- 

 ged, death ought to happen ; and then accordingly, 



* Memoirs on Respiration, p. 317. 



