918 SPECIAL PHYSIOLOGY. 



met. kils. Allowing 8 hours' work out of the 24, the daily work of a Man 

 would be 201,600 met. kils. (Redtenbacher.) The average work per second, 

 throughout the day, would be 2.3 met. kils. 



In the steam engine, the amount of heat evolved by the fuel consumed, is 

 sometimes 30 times, and, in the most economical engines, 20 times, greater than 

 the quantity converted into useful mechanical work ; theoretically, the utmost 

 available mechanical power is only y^th part of that producible by the heat of 

 the coal consumed. But in the human body, the economy of combustible ma- 

 terial is much greater. The total amount of heat given off from the body, in 

 24 hours, has been shown to be from 2,500,000 to 2,750,000 heat-units. The 

 former or smaller quantity would lift a corresponding number of grammes, or 

 2500 kilogrammes, to a height of 424 metres; and would, therefore, yield a 

 mechanical equivalent of about 1,060,000 met. kils., or about 5 times as much 

 as that which is requisite for the total daily work, viz., 250,000 met. kils. 

 Whilst, therefore, in an engine ^th part only of the fuel consumed is utilized 

 as mechanical power, |th of the food absorbed by Man is so appropriated. 

 This latter proportion agrees with Helmholz's calculations. 



Relations of the Kinds of Food, to the Modes of Work. 



The calorific arid mechanical work of the body, being thus under- 

 stood to have their immediate source in the power stored up in the 

 food, and in the oxygen of the air, and which is set free on the occur- 

 rence of chemical combination between them, after such food is assimi- 

 lated into blood or tissue, it may be admitted that, allowing for cer- 

 tain errors of calculation and deficiencies of knowledge, the numerical 

 or quantitative method shows that sufficient matter is oxidized in the 

 body, to account for both those modes of work. It must, however, 

 next be inquired, what are the relations of the different kinds of food 

 to these two different modes of work. 



It has long been observed that the carbon in the carbhydrates and 

 hydrocarbons, or amyloids and oleoids of the daily food, greatly ex- 

 ceeds that contained in the nitrogenous or albuminoid food. In Table 

 A, p. 901, the ratio is shown to be 7.64 to 2.29, or rather more than 

 3 to 1 ; the number of heat-units developed by the former would of 

 course be proportionally large. If to this carbon be added the hy- 

 drogen not united with oxygen, this portion of the food seems to be 

 the obvious source of calorific power in the body. Vierordt remarks, 

 indeed, that, if from the carbon and hydrogen of the nitrogenous food, 

 enough of those elements be deducted to form the urea excreted by 

 the kidneys, a quantity remains, totally insufficient to develop the heat- 

 units necessary for the calorific work ; for then only 57.3 grammes of 

 carbon and 6.3 grammes of hydrogen, will be left, which, multiplied 

 by their heat coefficients 8080, and 34,460, yield a total number of 

 680,082 heat-units, which is only about Jth of the required daily 

 amount, viz., 2,500,000. The non-nitrogenous food, in accordance with 

 the general opinion, is therefore, regarded as the essential source of the 

 animal heat. Indeed, 22 oz. of starch alone, not an unusual quantity 

 in certain daily dietaries, Tables, p. 920, would yield, 2,187,000 heat- 

 units. 



As regards the mechanical work, it is well known that this, whether 

 internal or external, involuntary or voluntary, is performed through 

 nervo-muscular action; that this implies fatigue and waste of the mus- 



