upon the air ; and, in their spontaneous decomposi- 
tion, all animal substances were found by Priestley 
(145.) and Spallanzani * to exert a similar operation. 
Now, by all these animal compounds carbon must 
have been furnished, and the mode of its separation 
from ^the other ingredients, and of its combination 
with oxygen, we conceive to be similar to what has 
already been stated (632.) to happen in the decom- 
position of vegetable bodies. Certain degrees of 
moisture and of heat are necessary to the exertion of 
this reciprocal action between animal substances and 
the air ; and it is, we conceive, by the gradual ope- 
ration of these agents that the animal carbon is re- 
leased from its existing combination, and brought 
into a condition capable of uniting with the oxygen 
gas of the air. We therefore suppose a spontaneous 
change in the animal substance to precede the che- 
mical union of its carbon with the surrounding oxy- 
gen ; and, consequently, this carbon may be consi- 
dered rather to separate from the other ingredients, 
than to be removed by the attractive force of oxy- 
gen. 
670. In support of this opinion, it may be observ- 
ed, that, provided due degrees of moisture arid heat 
be supplied, animal substances are prone to change, 
whether oxygen gas be, or be not, present ; and 
consequently, that gas is not essential to the separa- 
tion of the elements of the compound. Undoubted- 
ly, the presence of oxygen will greatly modify both 
the nature and extent of the changes which may take 
Rapports, &c. passim. 
