138 ANALYTIC SECT. XVII. 
carbonie acid expired, is therefore equal to that 
of the oxygen inspired, as Messrs. Allen and 
Pepys have proved in the Philosophical Transac- 
tions of London. 
cccxxxvul. The belief, that air is absorbed in the 
lungs, is of great antiquity, and was maintained 
also by Mayow, Willis, Borelli, and a crowd 
of others. Priestley and Lavoisier advocated suc- 
cessively the absorption of oxygen by the blood ; 
but this assumption rests on no better evidence 
than the then imperfect analysis of carbonic acid, 
whose composition Lavoisier estimated at seventy- 
two of oxygen, and twenty-eight of carbon; but 
which later chemists value at two of oxygen, 
and one of carbon by weight; or, to speak in the 
present language of chemistry, one atom of 
carbon is combined with two of oxygen. 
cecxxxvul. The surplus of oxygen which 
Lavoisier’s analysis of respired air gave, he sup- 
posed was partly absorbed by the blood, and the 
remainder combined with hydrogen, to form 
water. 
cccxxxIx. Most fluids contain a greater or 
less quantity of the atmospheric gases, and there 
is not a doubt that the blood always contains 
some carbonic acid; but of what has been called 
oxygenation of the blood, there is no valid 
proof; it is, on the contrary, refuted by direct 
experiment. 
