336 Generation affixed Air in tie Lungs. [Book IX, 



inflammable air was abforbed, and foul air improved, 

 by exp'ofure to arterial blood. It has alib been proved, 

 that inflammable air will produce a change of colour 

 in the blood, when introduced into the veins of a living 

 animal. 



The moil remarkable change produced on air, which 

 has been fubfervient to refpiration, is the difappear- 

 ance of the vital air, and the produftion of fixed air. 

 On account: of the production of fixed air, indeed, an 

 animal can only breathe a given quantity of air for a 

 certain time, after which it fickens and dies. If a jar 

 filled with vital air is placed over mercury, and an 

 animal confined in it, after a time it will be obferved 

 to breathe with diincuky, and become very uneafy 5 

 if the animal is then taken out, and cauftic alkali is in- 

 troduced, a great diminution in tiie bulk of the air will 

 take place ; by the repeated introduction of the ani- 

 mal and the caudle alkali, almoft the whole of 

 the air may be made to difappear, which proves 

 that the vital air is by refpiration converted into fixed 

 air. 



"When we confider the compofition of fixed air, 

 which confifts of the carbonaceous principle united with 

 oxygen, we muft conclude that the oxygen gas is con- 

 verted into fixed air by the addition of that principle, 

 which, in a ftate of extreme divifion, fecfns to be ex- 

 tricated from the lungs. By fome phyfiologifts, the 

 extrication of this noxious principle has been confidered 

 as the only end anfwered by refpiration. That this is 

 not all, however, is proved by the confideration, that 

 though part of the oxygenous gas is converted into 

 fixed air by the audition of the carbonaceous principle, 

 yet the weight of the air expired does not exceed that 

 which is infpired. This naturally fuggefted the opi- 

 nign, that a part of the infpired air was abforbed, nearly 



correfponding 



