HERMANN VON HELMHOLTZ 



for the times mentioned. In reality, however, besides 

 the production of mechanical effects, there is in the 

 animal body a continuous generation of heat. The 

 chemical force contained in the food and inspired 

 oxygen is therefore the source of two other forms of 

 power, namely, mechanical motion and heat ; and the 

 sum of these physical forces produced by an animal is 

 the equivalent of the contemporaneous chemical process. 

 Let the quantity of mechanical work performed by an 

 animal in a given time be collected and converted by 

 friction or some other means into heat ; add to this 

 the heat generated immediately in the animal body at 

 the same time, we have then the exact quantity of 

 heat corresponding to the chemical processes that have 

 taken place. 



4 In the active animal the chemical changes are 

 much greater than in the resting one. Let the 

 amount of the chemical processes accomplished in a 

 certain time in the resting animal be .*, and in the 

 active one be x +y. If during activity the same 

 quantity of heat were generated as during rest, the 

 additional chemical force y would correspond to the 

 work performed. In general, however, more heat is 

 produced in the active organism than in the resting 

 one. During work, therefore, we shall have * plus a 

 portion of y heat, the residue of y being converted into 

 mechanical effect. 



' The maximum mechanical effect produced by a 

 working mammal hardly amounts to one-fifth of the 

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