A 02 THE POPULAR SCIEXCE MONTHLY. 



Hess, the temperature of deep vessels and the cavities of the heart. IIo 

 showed that blood, in passing out from the kidneys, is warmer than 

 when it enters, and the same is true of blood passing through the 

 liver, lie ascertained, too, that the vital fluid is chilled in going through 

 the lungs, and consequently the temperature of the left cavities of the 

 heart is lower than that of the right, by an average of two-tenths of a 

 degree. The last fact clearly proves that the lungs are not the-ur- 

 nace of animal heat, and that the blood, in the act of revivification, 

 grows cool instead of warm. 



Ancient physiologists supposed that life has the power of producing 

 heat ; they conceived of a kind of calorific force in organized beings. 

 Galen imagined that heat is innate in the heart the chemic-physicians 

 attributed it to fermentations, 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 experiment, As early as 1777 he 

 discovered that air, passing through the lungs, undergoes a decompo- 

 sition identical with that which takes place in the combustion of coal. 

 Now, in the latter phenomenon, heat is thrown oft"; " therefore," says 

 Lavoisier, " there must be a like release of heat in the interior of the 

 lugs, during the interval between inspiration 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 beinjx 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 cf modern chemistry ; but he did not rest there. lie under- 

 took 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 developed 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 ascer- 

 tained in this way that such equality does not exist, nor was he long 

 surprised at this, for he soon discovered that, of 100 parts of atmos- 

 pheric oxygen absorbed, only 81 are thrown off by the breath in the 

 form of carbonic acid. He concluded 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 

 water contained in the expired air. Animal heat must be accounted 

 for, then, by a double combustion : of carbon first, then of hydrogen ; 

 and respiration regarded as throwing off out of the animal carbonic 

 acid and vapor of water. 



Lavoisier's experiments have been repeated and varied, and his 

 conclusions' discussed in many ways for nearly a hundred years. 



