ALIMENTATION AND THE EXPENDITURE 159 



The proteids and the fats, therefoie, are greater producers of 

 energy according to the isodynamic than according to the 

 isoglucosic theory, by ^ more on an average : so that in sub- 

 stituting them for carbo-hydrates in a ration, they will be 

 insufficient or sufficient according to the theory adopted. 

 Chauveau found that, for a dog undergoing exercise, the isoglucosic 

 estimation was the more correct, the other led to a diminution 

 in weight of the animal. ( x ) On the other hand, numerous 

 experiments of Atwater on man have shown, for instance, that 

 there must be 2,874 Calories for the dynamic expenditure of work 

 equivalent to 522 Calories, ff the ration is rich in carbo-hydrates ; 

 while 2,907 Calories are needed if the ration is fat, this estimation 

 being isodynamic. This difference of 33 Calories signifies that, 

 to cover its expenditure, the organism has transformed some 

 fats into glucose with a waste of 33 Calories. The waste increases 

 when the quantity of carbo-hydrates in the ration is reduced, ( 2 ) 

 and especially as the body of the subject loses its glycogenic 

 reserve. The intervention of this reserve can falsify the cal- 

 culations in cases where the ration contains few carbo-hydrates. ( 3 ) 

 Generally, the liver is a reservoir of glycogen which nourishes the 

 muscles (Claude Bernard) and which feeds them at the moments 

 when those muscles perform mechanical work. The proof is, 

 that the respiratory quotient, about 0-85 in a mixed alimentation, 

 is raised during work. 



Carbo-hydrates appear, therefore, to have all the characteristics 

 of a combustible beneficial to the muscular motor and to be the 

 direct sources of its mechanical energy. It will be remembered 

 (vide 37) that the energy resulting from any chemical reaction 

 consists of the " free " energy, which can be utilised to do work, 

 and " bound " energy, which is dissipated in heat. Carbo- 

 hydrates and glucose are examples of sources of free energy. 

 The external work of the muscles, and the internal- work of the 

 organs (minimum expenditure of energy) utilise this form of 

 combustible. 



(*) A. Chauveau (Comptes Rendus Acad. Sciences, 1897). 



Atwater and Benedict (Bulletin, No. 136, pp. 184-5, 1903). 



( 3 ) Atwater and Benedict (Ibid., p. 189). 



