THE ANIMAL AS A PRIME MOVER. 319 



comparatively small amount, and, ifnecessary, made minute, by properly 

 clothing it in nonconducting materials, precisely as nature clothes the 

 birds and the other wild creatures. If the suppression of this loss 

 results in corresponding increase in energy- con version, in useful direc- 

 tions, the efficiency of the machine is to that extent exalted. It is 

 certain that some loss of heat externally is necessary to preserve the 

 activities of organs of the body, by giving a needed difference of tem- 

 perature between the surface and the interior, and to carry away 

 energy in its final, thermal form; and mankind has, from the begin- 

 ning, sought to reduce this waste by covering the body with skins, 

 woven tissues, and other forms of material fitted to check the outflow. 



The source of animal warmth and heat energy has been for genera- 

 tions the subject of study and experimental research by the best 

 physicists and biologists. According to Jamin, Messrs. Halles and 

 Cigna and Black and Priestley showed that the products of respiration 

 were chemically identical with those of combustion. Lavoisier con- 

 firmed this conclusion, and proved that the oxygen inhaled was not all 

 accounted for by the exhalation of carbon-dioxide, but a balance must 

 be sought in the production of water by union with hydrogen. He 

 attributed the vital functions to the oxidation occurring in the lungs, 

 and circulation to digestion and to the regulating action of transpira- 

 tion. Kegnault and Eeiset, measuring the volumes of carbonic acid 

 produced, found that the larger the proportion of vegetable food the 

 greater the amount of this oxidation ; while the combination of oxygen 

 directly with the carbon of the nutriment sometimes gave an item in 

 the balance of the account, its rejection occurring with the fluids of the 

 system, as in uric acid, this proportion being the greater as the food 

 was, in larger part, flesh. They found a small amount of nitrogen 

 passing off, presumably rejected from the disintegrating tissues. Bous- 

 singault reached the same conclusion by determining the quantities of 

 solid and liquid taken into the body and rejected from it. Lagrange, 

 Spallanzani, Edwards, and Magnus ascertained that the oxidation 

 occurs in the circulation and the capillaries. Despretz and Dulong 

 found the heat produced by the vital apparatus to be about nine-tenths 

 the quantity which would result from complete oxidation, in equal 

 amount, in the air. 1 



The source of vital and muscular energy is easily identified, and it is 

 well known that the function of digestion is to render available the 

 potential energy of the foods by reducing them to solution in fluids 

 capable of easily and rapidly and completely entering the constitution 

 of the blood, to be distributed to points in the system at which their 

 stores of potential energy may be made available in kinetic form. Pre- 

 cisely how this latter operation of transformation occurs is still un- 

 known; but Claude Bernard, about the middle of the century, called 

 attention to the action of the hepatic system in the production of glyco- 



An interesting corroboration of recent measures of the coefficient of digestion. 



