HEAT AND LIFE. 137 



of heat that had hitherto escaped notice. Berthelot shows 

 that carbonic acid in the system is not always formed by 

 oxidization of carbon, but sometimes proceeds from de- 

 composition absorbing heat. We know that alimentary 

 substances are reducible to three fundamental types fats, 

 hydrates of carbon (sugars, fecula, starch), and the albumi- 

 noids. Now, the fats, in decomposing and combining with 

 water, as it occurs under the influence of the pancreatic 

 juice, evolve heat ; and so it is with the hydrates of carbon, 

 independent of any oxidization. And albuminous sub- 

 stances, too, produce very clear calorific phenomena, when 

 their combination with water takes place with its conse- 

 quent various decompositions. These facts, noted by 

 Berthelot, must have their place in the minute and exact 

 calculation of animal heat, which it is perhaps as yet too 

 early to undertake. At any rate, this heat originates in 

 the totality of those chemical transformations which are 

 going on unceasingly in the depths of the animal organs, 

 and are bringing about the continual renovation of the 

 whole organized substance ; in other words, nutrition ; 

 but why that nutrition why that perpetual production of 

 heat in the living machine ? 



We have now the means of answering this question, 

 which involves the secret of one of Nature's most beautiful 

 arrangements. The heat produced by animals is the source 

 of all their movements ; in other words, the mechanical 

 labor they perform is a mere simple transformation of the 

 activity of heat they develop. They do not create motive 

 force by any voluntary operation, which would be one of 

 the prerogatives of life ; they draw it from the calorific en- 

 ergy stored up in the organs traversed by the blood. Be- 

 sides, there is a fixed relation between the quantity of heat 

 that disappears and the mechanical labor that appears. 

 Yet it is to be remarked that, if all motion by living beings 

 is a transformation of animal heat, that heat is not wholly 

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