264 
duced, in the same time, 132 parts of carbonic 
acid *. 
553. The fact of the disappearance of a portion 
of the air in this experiment we do not dispute ; nei- 
ther do we question the accuracy of the analysis of 
the air which was actually obtained ; but to the no- 
tion that the air, which disappeared, was absorbed 
by the animal system, we cannot so readily accede. 
No reasons, either anatomical or chemical, are as- 
signed in support of such an opinion ; neither is any 
evidence offered of the existence of these gases in the 
animal system, nor of their subsequent expulsion 
from it. The mere loss of a part of the oxygen 
seems to have afforded sufficient proof that the whole 
of it had first been absorbed ; and that the portion 
of it, not returned in the form of carbonic acid, was 
permanently retained in the system. We forbear to 
repeat the general arguments against an absorption, 
or attraction of air by the gills of fishes, which have 
been already stated (74.5), but shall notice a few 
sources of fallacy in these experiments, which may, 
perhaps, explain the manner in which a part of the air 
might disappear, without resorting to the improba- 
ble supposition of its absorption. 
554. The means of ascertaining with absolute pre- 
cision, the volumes of air before and after respiration, 
have always constituted the great difficulty in experi- 
ments on this function, even in terrestrial animals ; but 
as the sources of fallacy have been successively de- 
tected and removed, the correspondence between the 
* Mrm. d'ArcuMl. torn. ii. p 376. 
