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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