136 THE HUMAN MOTOR 



are called proteids or azotes, and to indicate that they contain 

 albumen, " albumenoids." 



The combustion of an immediate principle developes heat, 

 a definite number of calories per gramme of the substance. 

 This number measures as has already been said ( 34) " the 

 heat of combustion." Its determination is made in practice by 

 burning a certain weight of the substance with oxygen, in a 

 special apparatus : " Berthelot's or Fery's calorimeter." The 

 operation is violent and complete. But it is known that, in the 

 human organism, reactions are gradual, and the aliment is not 

 completely used up, for it leaves a residue capable of liberating 

 more energy : the digestive transformations do not conduct the 

 whole of the absorbed aliment to the cells. Also, each principle, 

 each substance, or mixture of substances, possess " co-efficients 

 of digestibility," or " co-efficients of proper nutritive utilisation " : 

 by that, is meant the ratio of the quantity really utilised in 

 cellular work, to the total quantity introduced through the 

 mouth. Finally the "proteids" in their combustion furnish 

 almost exclusively " urea," a substance not devoid of energy, 

 that is to say, their combustion is incomplete. 



Taking everything into account, it is found that the " calorific 

 power " of food is inferior to the heat of combustion the former 

 being deduced from direct measurements on man and animals. 



If we leave out of account the co-efficient of digestibility and 

 consider only an organism burning its own reserves (the case 

 of inanition), the calorific power would coincide with the heat 

 of combustion of those same reserves, as there would be no 

 waste. 



96. Composition of Foods. 1. Carbohydrates. These are : 

 cellulose, starch, dextrine, sugars, glycocine, gums, and mucilages. 

 They abound in the " feculents " and the " farinaceous foods " 

 (potatoes, rice, etc.) They are eaten almost pure (honey, syrup) 

 or absolutely pure (sugars). Their "co-efficients of digestibility " 

 vary between -9 and 1-. Experiment has given 4-1 calories per 

 gramme of food ( l ) as their calorific power. 



(*) The determination of calorific power was initiated by Rubner in 

 Germany (Zeitsch. f. BioL, 1885, vol. xxi., pp. 250 and 377). Since 1896 

 the Department of Agriculture, Washington, has published, under the 

 direction of Atwater and his collaborates, a series of researches on the 

 alimentation and labour of man. The title of these publications is Pro- 

 ceedings of the American Agricultural Colleges and Experiment Stations. 

 They fill numerous numbered and dated bulletins. We shall often utilise 

 them, quoting the number of the bulletin, the page, and the date. Since 

 the death of Atwater (1908) Benedict directs this scientific enterprise. 

 The institution also publishes numbered Publications distinct from the 

 bulletins. 



