THE ANIMAL AS A PRIME MOVER. 301 



largely, and of other essential matter in less proportion. On the other 

 hand, the muscle and nerve and bone-making constituents alone serve 

 to build up the machine, but not to operate it. Ultimately, however, it 

 is supposed that the stored energy of the latter class of compositions 

 become available, and thus both, the original proportions being correct, 

 may have a kind of measure of value in that of their fuel constituents. 

 For highest efficiency, the proportions of the constituents must be suit- 

 able for the individual case, and availability by digestion and assimila- 

 tion, and in the provocation of all essential vital processes, is quite as 

 essential as either of the other required qualities of the food. 



The protein compounds are all nitrogenous, whether in the form of 

 albumen, fibrin, casein, or gluten. These compounds are fairly uni- 

 form in value. The carbohydrates differ greatly among themselves in 

 this respect. The fats are substantially of equal value as measured by 

 thermal contents, but differ in palatableuess and digestibility, and thus 

 in food value. Neither the carbohydrates nor the fats contain nitrogen, 

 and they are simply useful in furnishing a supply of heat or other 

 energy. One unit weight of carbon and one of protein yield substan- 

 tially equal quantities of energy — about 14,500 British thermal units, or 

 1,860 calories per unit weight. Its energy is sufficient to raise 2,850 

 tons one foot high. The same weight of carbohydrate has usually very 

 nearly the same force value. A similar weight of fat should have 50 

 per cent more stored energy — about 4,700 foot-tons. A pound of corn 

 meal should supply a quantity of energy equal to two-thirds that of an 

 equal weight of carbon — about 2,080 foot-tons, 1,360 calories. 



The food consumed daily by a powerful workiugman contains, on the 

 average, about 3£ ounces of protein, 6 ounces of fat, and 14 ounces of 

 carbohydrates, according to Professor Woods. Its energy measures 

 sensibly the same as that of 2£ pounds of coin meal. Its protein and 

 fats come largely from the flesh food contained in the daily ration. 

 The carbohydrates come entirely from the vegetable constituents. 

 Another illustrative example of a ration given by the same authority 

 measures 3.8 ounces of protein, 5 ounces of fat, 15 ounces of carbo 

 hydrates. The energy stored in the food thus taken measured 5,400 

 foot tons, or 3,530 calories. A standard ration for swine contains about 

 7,500 foot-tons, 4,900 calories, per 100 pounds weight. That for cows 

 measures 4,600 foot-tons, 3,000 calories, approximately, per 100 pounds 

 weight. The ration for sheep measures 5,900 foot-tons and 3,550 

 calories per 100 pounds. 



Food-energy transformation is the office of the vital machine. The 

 fish can traverse the water all day; the bird can fly through the air all 

 day; man and the animals on land can walk all day; and it is evident 

 that, as suggested by Pettigrew, their tasks must be not very far differ- 

 ent in magnitude. All exert powers approximately proportional to the 

 volume of the seasoned working muscles employed in these tasks, which, 

 according to various authors, is not far from about the equivalent in 



