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98. Does then the carbonic acid, which is here 

 met with, proceed ready formed from the blood, or 

 is it in part formed by the decomposition of the air ? 

 No one has yet proved -that any aeriform fluid, much 

 less that carbonic acid, exists naturally in the blood ; 

 and if this be true, no such aerial acid can be ex- 

 pected to issue from it. The carbonic acid also, is 

 not formed by blood when it is confined in nitrogen 

 gas ; neither does the colour of the blood, in that 

 case, undergo any sensible change : but this acid is 

 formed by blood, either in oxygen gas, in nitrous 

 oxide, or in atmospheric air, all of which are dete- 

 riorated thereby ; whence it follows, that without 

 the presence of oxygen gas, the blood is unable to 

 form carbonic acid, and that this acid, therefore, is, 

 in part, formed out of that gas. If the oxygen gas 

 that disappears do not contribute to form the carbo- 

 nic acid [hat is produced, in what other manner can 

 its loss be accounted for ? or from what other source 

 than the oxygen gas of the air, in contact with the 

 blood, >can that ingredient of the acid be derived ? 

 Those who suppose the carbonic acid to be furnish- 

 ed by the blood, independent of the air employed, 

 must likewise suppose that the nitrogen gas is fur- 

 nished by it also ; for the experiments of Mr Davy 

 teach us, that a portion of that gas, as well as of 

 carbonic acid, is always present when nitrous oxide 

 is decomposed, which renders it probable that the 

 same thing likewise occurs when air is changed by 

 venal blood. But in what manner the blood should 

 be able to furnish nitrogen gas, it is not easy to con- 

 ceive, since no affinity exists between that gas and 



