HEAT AND LIFE. 



405 



Of late years, the question has been taken up again with more ex- 

 actness, thanks to the views of a new science called " heat-chemistry," 

 which occupies itself with chemical phenomena in their relations to 

 heat. Heat-chemistry, by the aid of very delicate apparatus for meas- 

 uring heat, ascertains the number of heat-units developed or absorbed 

 by bodies entering into combination, beginning with the noted experi- 

 ments of Favre and Silbermann. Berthelot, who had made profound 

 researches into this subject, reduces the sources of animal heat to live 

 varieties of transformation : first, the effects resulting from the fixation 

 of oxygen with different organic principles ; then the production of car- 

 bonic acid by oxidization ; then the production of water ; in the fourth 

 place, the formation of carbonic acid by decomposition ; and, last, hy- 

 drations and dehydrations. The learned chemist attempted to show 

 how the numbers obtained in the study of the heat of combustion of 

 the different organic acids, alcohols, etc., might be applied to the com- 

 pounds burned in the animal organism ; but, while admitting the theo 

 retic verity of the analogies he establishes, we cannot refrain from re 

 marking that their practical verification is exceedingly delicate and 

 difficult. How can we measure, at any one point of the system, the 

 heat produced by a fleeting reaction occurring in the inmost depths of 

 a tissue that must be lacerated to be examined ? 



If thermo-chemistry seems not to throw much light on physiology 

 on this side, it reveals to it on another sources 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 decomposition absorbing heat. We know that alimentary sub- 

 stances are reducible to three fundamental types fats, hydrates of 

 carbon (sugars, fecula, starch), and the albuminoids. Now, the fats, 

 in decomposing and combining with w T ater, as it occurs under the influ- 

 ence of the pancreatic juice, evolve heat ; and so it is with the hy- 

 drates of carbon, independent of any oxidization. And albuminous 

 substances, too, produce very clear calorific phenomena, when their 

 combination with water takes place with its consequent various de- 

 compositions. 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 unceas- 

 ingly 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 transforma- 

 tion of the activity of heat they develop. They do not create mo- 



