UTILISATION OF FOOD AND ENERGY 109 



(2) The relation between metabolism and muscular 

 work. 



It has been shown already (p. 48) that each 

 nutrient brings to the animal a certain quantity of 

 utilisable energy. As a measure of this energy the 

 quantity of heat which remains after deducting that 

 contained in the excreta is taken. It is usual 

 to express this quantity of energy by a certain 

 number of heat units or calories. The metre- 

 kilogram (foot-pound in British units) is taken as 

 the standard by which to measure the work of an 

 animal or a machine, and is the quantity of energy 

 necessary to raise one kilo one metre high (or one 

 pound one foot high). 



From exact experiments it has been satisfactorily 

 ascertained that the energy of one large calorie (Cal.) 

 in its transformation into kinetic energy can per- 

 form 425 metre-kilograms work. 



If an animal were able to convert all the available 

 energy contained in the nutrients into muscular work, 

 one kilo starch, which brings 376 Cal. into the body, 

 would be able to yield energy for, in round figures, 

 1600 mkg. work. From investigations carried out 

 on this branch of the subject it has been found that 

 only one-third of the available energy in the food 

 is obtained in the form of utilisable work. In ten 

 different experiments on a man who performed 



