132 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 in it. 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 in a corresponding 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, 



