261 
the nitrogenous portion of the air remained unalter- 
ed. In temperatures at or below zero, no change 
however was produced in the quality of the air *. 
We repeated these experiments on the pupae of the 
common fly, and found, that, during their transfor- 
mation, they consumed all the oxygen gas of the air 
in which they were confined, and produced an equal 
volume of carbonic acid. 
550. IT has been already shewn (63.), that Fishes 
require the presence of oxygen gas in the water in 
which they live, and convert it into carbonic acid. 
These facts have been confirmed by the experiments 
of M. Sylvestre f> and by those of Spallanzani. 
The latter philosopher ascertained, by experiment, 
that fishes consume oxygen gas and produce carbo- 
nic acid, when confined either in water or in air ; 
that they lose their vivacity, but do not become le- 
thargic under cold, and then consume much less oxy- 
gen ; and that oxygen gas is changed into carbonic 
acid by their skins, as well as by their gills. Their bo- 
dies, also, act upon the air after death, and, Kke 
other animal substances, consume its oxygen under 
decomposition J. 
551. We are indebted to M. M. Humboldt and 
Provencal, for experiments on the respiration of 
fishes, which possess still greater accuracy. Their 
* Rapports, &c, torn. i. p. 44. 50. 
f diver's Lemons d'Anat. comp. torn, iv. p. 305, 
! Rapports, &c, t. i, p. 18ft. 
