444 THE POPULAR SCIENCE MONTHLY. 



the body may waste for a lengthened period and yet live, it rapidly 

 dies when the source of heat is removed or even greatly lessened. 



The production of heat in the body, so wonderful in the process 

 and amount, results only from the chemical combination of the ele- 

 ments of food, whether on the minute scale of the atoms of the several 

 tissues, or on the larger one connected with respiration, and is thence 

 called the combustion of food. As familiar illustrations of the pro- 

 duction of heat from chemical change, we may mention that, when 

 cold oil of vitriol and cold water are added together, the mixture be- 

 comes so hot that the hand cannot bear it, and the heating of hay- 

 stacks, and also of barley in the process of malting, is well known. 

 This action in the body is not restricted to changes in one element 

 alone, but proceeds with all ; yet it is chiefly due to a combination of 

 three elements, viz., oxygen, hydrogen, and carbon, and requires for 

 its support fat, starch, or sugar, or other digestible food composed of 

 those substances, precisely as coal and wood supply fuel for lire with- 

 out the body. 



This effect is made extremely striking, by Prof. Frankland, in the 

 following table, which shows the amount of heat generated from so 

 small a quantity as ten grains of certain foods during their complete 

 combustion within the body, and the force which scientific calculations 

 have shown to be equivalent to that amount of heat. The original 

 quantity used by Prof. Frankland has been reduced by Dr. Letheby to 

 ten grains, for the convenience of English readers : 



No. l. 



FOOD. 



10 grains of dry flesh 



" " albumen... 



" lump-sugar. 



" arrow-root. 



" " butter 



" " beef-fat . . . 



In combustion raises 



Which is equal to 



Thus we prove that an ounce of fresh lean meat, if entirely burned 

 in the body, would produce heat sufficient to raise about 70 lbs. of 

 water 1 Fahr., or a gallon of water about 7 Fahr. In like manner, 

 one ounce of fresh butter would produce ten times that amount of 

 heat ; but it must be added that, as the combustion which is effected 

 within the body is not always complete, the actual effect is less than 

 that now indicated. 



It may thus be shown that the division of foods into the two great 

 classes of flesh-formers and heat-generators is not to be taken too in- 

 cisively, for while a food is renewing flesh it also produces heat, and 

 while the heat-generating food is acting it may also produce a part of 

 flesh in the form of fat ; but, although they are so closely associated 



