160 THE HUMAN MOTOR 



When the total mechanical work is moderate, that is, when the 

 expenditure of free energy can be drawn solely from the carbo- 

 hydrates of the ration and the reserve ; or when the external 

 labour is zero, the subject only expending its minimum of energy 

 (that needed for the internal organs) the isodynamic condition 

 obtains ; the calculation of the rations being made exactly 

 according to the co-efficients indicated above : 4-10 Cal., 4-10 

 Cal., and 9-10 Cal. But, in the case of excessive work, and of a 

 ration and reserve poor in carbo-hydrates, isoglucosics intervenes 

 to make up the deficit, by its glucose forming operations (glyco- 

 genetics). 



These two theories supplement and correct each other, and they 

 show that, when studying a living motor, it is always necessary 

 to give it food sufficient in carbo-hydrates. The " bound " energy 

 taken indifferently from one of the three alimentary substances, 

 maintains the body at a constant temperature. Thus it i? clear 

 that there is a carbo-hydrate minimum 



Rubner ( J ) made some curious experiments on this point, by 

 keeping an animal in a surrounding atmosphere of 37 C. after 

 having freed it of its glycogenic reserves by a prolonged fast. 

 He then observed that if the animal in repose expends 100 calories 

 of carbo-hydrates for its maintenance (internal work) this physio- 

 logical expenditure will be increased by 13 calories at the expense 

 of the body with a diet of fats, and will be 131 calories if the ration 

 is proteid. 



Thus the minimum physiological expenditure is : 



For 100 calories of carbo-hydrates, 100 calories of " free " 

 energy. 



For 100 calories of fats, 13 calories of "bound" energy and 87 

 calories of "free" energy. 



P'or 100 calories of proteids, 31 calories of "bound " energy and 

 69 calories of "free " energy. 



The waste is therefore zero in the first case, or practically so 

 (it would be absolutely zero in a glucose ration.) It follows 

 that the expenditure of 100 calories of free energy, or carbo- 



100 X 100 



hydrates corresponds to - = 115 calories furnished in 



o7 



100 x 100 

 fats and - - -145 calories in proteids. Rubner gave the 



name of "specific dynamic actions" to these wastes, equal 

 respectively to 15% and 45%. Work uses the most economical 

 form of energy. 



f 1 ) Max Rubner, Die Gesetze des Energieverbrauchs bei der Ernahrung, 

 p. 334 and Chaps, xvii. and xviii., Leipzig, 1902). 



