124 



blood. We incline, therefore, to the opinion, that 

 neither the air nor its oxygen gas is attracted by, 

 and diffused through the blood, as happens with se- 

 veral gases when placed in contact with certain fluids: 

 but that the air is decomposed, and its oxygen gas 

 changed into carbonic acid, without entering into 

 the substance of that fluid. 



100. But, for the formation of this acid, the blood 

 must supply carbon, since no other substance was 

 present from which it could be derived r and it is well 

 known also, that carbon enters largely into the com- 

 position of that fluid ; and our experiments (97.) 

 prove, that it exists as well in the serous as in the 

 more solid parts. By some it may be objected, that 

 because carbonic acid is formed directly by the com- 

 bustion of charcoal, it cannot be produced at so low 

 a temperature as exists in these experiments. To 

 this we can reply only by an appeal to the general 

 facts exhibited through the whole course of our in- 

 quiry, by which it appears, that both by the living 

 functions of vegetables and animals, and by the de- 

 composition of animal and vegetable matter, this acid 

 is, in like manner, formed at temperatures equally 

 low. Even those who consider this acid to have 

 proceeded ready formed from the blood, cannot at- 

 tribute its production to the operation of heat ; for 

 in the animal body, the temperature of the blood 

 seldom exceeds 1OO a degree of heat incompetent 

 to form carbonic acid by any process analogous to 

 combustion. The combination of many bodies is, 

 indeed, greatly accelerated by being exposed to very 

 high temperatures ; but this surely does not set aside 

 the fact of their spontaneous union at temperatures 



