1352 NATURE AND LIFE. 
mentations, the mechanic-physicians to frictions. Time has 
dispelled these errors of supposition, and it is proved now 
that the heat of animals proceeds from chemical reactions 
taking place in the interior of the system. Lavoisier must 
be credited with the demonstration of this truth by experi- 
ment. As early as 1777 he discovered that air, passing 
through the lungs, undergoes a decomposition identical 
with that which takes place in the combustion of coal. 
Now, in the latter phenomenon, heat is thrown off; “ there- 
fore,” says Lavoisier, “ there must be a like release of heat 
in the interior of the lungs, during the interval between in- 
spiration and expiration, and it is doubtless this caloric, 
diffusing itself with the blood throughout the animal 
economy, which keeps up a constant heat init. There is, 
then, a constant relation between the heat of the living 
being and the quantity of air introduced into the lungs, to 
be there converted into carbonic acid.”’ Such is the first 
capital fact brought to light by the creator of modern chem- 
istry; but he did not rest there. He undertook to examine 
whether the heat theoretically produced in a given time by 
the formation of a certain amount of carbonic acid, that is 
to say, by the combustion of a certain quantity of carbon in 
the organism, is exactly equal to the amount of heat devel- 
oped by the animal inacorresponding time. This quantity 
was estimated by the weight of ice melted by the animal 
placed in a calorimeter. Lavoisier ascertained in this way 
that such equality does not exist, nor was he long surprised 
at this, for he soon discovered that, of one hundred parts 
of atmospheric oxygen absorbed, only eighty-one are thrown 
off by the breath in the form of carbonic acid. He con- 
cluded then, from this observation, that the phenomenon is 
not a simple one, that a part of the oxygen (nine per cent.) 
is consumed in burning hydrogen, to form the vapor of wa- 
ter contained in the expired air. Animal heat must be ac- 
counted for, then, by a double combustion—of carbon first, 
