182 EFFECT OF COMBUSTIBLE ALIMENT. 



ment of caloric which makes man what he is, and constitutes his special 

 prerogative ; his degree of skill therein is the measure of his civilization. 

 The distribution of plants and animals, or, rather, their limitation within 

 fixed boundaries, depends on the distribution of heat, but from these re- 

 straints man is free, because he can control temperatures. 



From these considerations of the effect of external heat on the human 

 mechanism, we return to a more critical examination of the modes by 

 which heat is generated, and its degree regulated in the body. 



In every instance we assert that the production of animal heat is due 

 Source of ani- to oxidation taking place in the economy, and giving rise to 

 mal heat. carbonic acid, water, and other collateral products. It is not 

 necessary to attach any weight to the experiments of Dulong, which seem- 

 ed to indicate that not more than four fifths of the heat actually pro- 

 duced could be owing to the oxidation of carbon, nor to those of a like 

 kind of Despretz. The method they resorted to for the measurement of 

 the disengaged heat was open to error ; the numbers they employed as 

 representing the combustion heats were incorrect ; nor did they make any 

 allowance for other substances, such as sulphur and phosphorus, which 

 are simultaneously oxidizing, and the products of their combustion escap- 

 ing by the kidneys. 



Eeduced to its ultimate conditions, the evolution of animal heat de- 

 Effect of more pends on the reaction taking place between the air intro- 

 aiSient^w^ai- ^ uce ^ ^7 respiration and the food, and as either one or other 

 cohoi. of these is touched, the result may be predicted. If, for ex- 



ample, into the digestive canal alcoholic preparations be introduced, they 

 are absorbed, by reason of their liquid condition and diffusibility, with 

 readiness. The combustibility of alcohol, and the amount of heat it 

 yields, are so great, that the primary effect of the oxidation which ensues 

 is a warmth or feverish sensation. By reason of the changes which are 

 now taking place so actively in it, the blood circulates with unwonted 

 rapidity, and the supply to the brain increasing, that organ exhibits an 

 unusual functional activity. But this display of intellection is only tem- 

 porary, and an opposite condition soon comes on, for, more carbonic acid 

 accumulating in the blood than the lungs can get rid of, the depressing 

 effects of that body commence, and eventually the symptoms of poison- 

 ing by it ensue. 



Not unlike this is the train of effects which arise when, instead of va- 

 Effectofamore rying the nature of the article ingested, we vary that of the 

 porter of respi- & as respired. An energetic supporter of combustion, like the 

 ration than air. protoxide of nitrogen, gives rise to a feverish glow, cerebral 

 activity, to be followed eventually by a deep depression, the poisonous 

 influence of the carbonic acid produced being exhibited. After a while 

 the system casts it off, and recovers its condition of health completely. 



