THE MUSCULAR MOTOR AND ALIMENTATION 133 



21% of the volume of the air. We must have, therefore, the 

 simultaneous presence of the combustible and of the combustible 

 supporting gas. The supply must be uninterrupted, and in 

 sufficient quantity to maintain the motor in movement. 



The action of oxygen, or oxidization is generally a rapid 

 phenomenon, accompanied by flame, and producing a great 

 quantity of heat in a short time, and causing an increase of 

 temperature. 



In the living motor, the combustible is the food, and the pheno- 

 menon of combustion is called nutrition. The name of meta- 

 bolisms is reserved for the whole series of transformations 

 which mark the evolution of food in the organism. There is no 

 essential difference between the combustion of coal in a grate 

 and that of food in the body. If oil could be burnt in our bodies, 

 it would develop there just as much heat as undei a boiler. If 

 alcohol oxydised itself in our organs, it would liberate the same 

 quantity of heat as in the cylinder of an internal combustion 

 engine. This point, lor a long time the subject of acute contro- 

 versy, is now definitely proved. 



Inter-organic combustion and all other combustions are of an 

 identical nature; they are oxidizations. 



At all times organic oxidization is slow ; it is not accompanied 

 by the emission of flame or an elevation of temperature. It takes 

 place in all living beings animal and vegetable at almost any 

 temperature, and in man at about 37 C. This extraordinary 

 phenomenon of a slow reaction, taking place at a low temperature, 

 is explained by the presence in the living tissues of oxydising 

 agents. Their function is to serve as " primers," or perhaps to 

 impart the small quantity of energy that a spark brings to an 

 explosive powder. These oxidisers have been isolated, but their 

 constitution remains obscure. 



94. Although the exothermic character of the reactions of the 

 whole of the organism may be indisputable, and the reality of the 

 cellular combustion raise no more doubt, a fundamental char- 

 acteristic distinguishes living beings from all mechanical heat 

 engines. In the latter the nature of the fuel is indifferent, pro- 

 vided that it burns. In the former, on the contrary, the only 

 acceptable food is that which the cells can assimilate and elabor- 

 ate in a certain manner. The combustible is " reserved " by the 

 organism, and thus it can undergo slow oxidization and become 

 the source of all the energies of the being. If this reserve is not 

 possible, the substance is rejected, and is useless as nourishment. 



This important fact is demonstrated in the case of fasting, 

 Where the subject lives on his own substance, that is to say, 

 develops heat and labour, without any help from outside aliments. 



