CHEMICAL THEORY OF ANIMAL HEAT. 881 



In the first accurate experiments on animals which were made by 

 Dulong and Despretz, a water calorimeter was employed. The ani- 

 mal was placed in a metal chamber, which was surrounded by a given 

 quantity of water inclosed in a still larger vessel ; air was conducted 

 to the internal chamber by one tube, whilst a second long spiral tube 

 passing through the water, like the condensing tube of a still, con- 

 veyed away the warm air, which, before it escaped, gave up its heat 

 to that fluid. The stream of air was rendered uniform by an appa- 

 ratus known as an aspirator, a large closed vessel filled with water, 

 and connected with the free end of the coiled air-tube, so that on the 

 gradual escape of the water from the aspirator, through a stop-cock, 

 air was drawn through the apparatus at a uniform rate. In the water 

 of the calorimeter itself, a moving fan agitated the fluid, so that its 

 temperature was kept uniform during the experiment. Lastly, the 

 air, as altered by the respiration of the animal, or a part of it, the 

 rest then being measured, was analyzed, in order to determine the 

 quantity of carbonic acid produced. It was, at that time, erroneously 

 supposed that this corresponded exactly with the quantity of oxygen 

 consumed. Rabbits or dogs were subjected to experiments, varying 

 from an hour and a half to two hours' duration ; and the results ob- 

 tained by Dulong and Despretz, showed that the amount of heat given 

 off was from Jth to Jth more than the quantity of carbonic acid pro- 

 duced would account for. In subsequent experiments, made by Des- 

 pretz alone, it was found that from ith to ^th of the heat was thus 

 unaccounted for. 



The excess in the heat actually produced by the animals experi- 

 mented on, was supposed to be accounted for, by the friction of the 

 heart and the muscles, by that of the blood in the vessels, by the dis- 

 engagement of heat taking place in the conversion of fluid into solid 

 matter in the nutrition of the tissues, and by some possible action of 

 the nerves. It has, indeed, since been shown, that heat is really given 

 out in muscular contraction. Nevertheless, these supposed causes of 

 animal heat are not primary, but secondary causes. The heat given 

 off in muscular contraction, is itself engendered by oxidation in the 

 blood of a muscle, or in the muscle itself, during the so-called paren- 

 chymatous respiration. The heat produced by mere friction in the 

 body, must have its source in muscular contraction, and this, as we 

 have just said, is due to chemical change or oxidation. The conver- 

 sion of fluid into solid substance, in the nutrition of the tissues, is, as 

 will be presently explained, an apparent, and not a real cause of in- 

 ternal heat; and lastly, any influence of the nervous system is indi- 

 rect, operating only by exciting organic processes, themselves involving 

 oxidation. 



The deficiency of heat-producing power in the quantity of carbonic 

 acid given off" by the animals experimented upon by Dulong and Des- 

 pretz, in comparison with the heat which they simultaneously evolved, 

 may be otherwise accounted for. In the first place, these observers 

 did not determine the temperature of the animals before and after each 

 experiment, which might have shown some retention of heat. But 

 other points are of more moment. The modern researches of Favre 



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