276* 
565. In the year 1806 Mr Daltou's. attention was 
directed to this subject, and he satisfied himself, by 
numerous experiments, that the bulk of carbonic 
acid, formed hi respiration, was exactly equal to that 
of the oxygen gas consumed. On repeating these 
experiments, Dr Thomson obtained, in some cases, 
nearly the same results ; but, upon the whole, the 
bulk of oxygen that disappeared was somewhat great- 
er than that of the carbonic acid formed. The dif- ,. 
ference, however, varied considerably, and kept pace 
with the diminution in the whole bulk of air ; whence 
he considers it to arise from the abstraction of a part 
of the air by some other way than by respiration ; 
and if this be allowed for, he believes " the bulk of 
acid produced to be precisely equal to that of oxygen 
gas lost *. Hence, says he, this oxygen must be 
changed into carbonic acid in the lungs ; for oxygen 
gas, when changed into carbonic acid, does not sen- 
sibly alter its bulk ! 
566. These conclusions have been since confirmed 
by some very accurate experiments of Messrs Allen 
and Pepys. They caused a person to inspire, from 
a gasometer, 3460 cubic inches of atmospheric air, 
which were afterwards expired into another gasome- 
ter ; and to both gasometers graduated scales were 
affixed, by which the quantities of air received and 
expelled could be accurately measured. The time 
occupied in the experiment was eleven minutes : 
about 58 respirations were made ; and the deficiency 
in the whole volume of air, at the close of the expe- 
Syst. Cheir. vol. v..p. 736. 3d edit. f Ibid. p. 77 i. 
