THE LIVING ORGANISM 23 



greater part upon the combining power of its carbon 

 elements. The nitrogen atom makes the protein an 

 extremely volatile compound, so that the latter burns 

 readily in the tissue cells ; and the hydrogen and oxygen 

 bring their specific characteristics to the total molecule. 

 And furthermore, it is evident that the great complexity 

 of this constituent, protein, gives to protoplasm its 

 power of doing work, or, in a word, its power of living. 

 In constructing it, much energy has been absorbed and 

 stored up as potential energy, and so, like the stored-up 

 energy in a watch spring or in gunpowder, this may be 

 converted, under proper conditions, into the kinetic 

 energy and the work of actual operation. On account 

 of its peculiar and complex nature, it possesses great 

 capacity for burning or oxidization, thus serving as a 

 source of vital power. It burns in the living tissue just 

 as coal oxidizes in the boiler of an engine ; its atoms fly 

 apart and unite with oxygen so as to satisfy their chem- 

 ical affinities for this substance. If we could only see 

 what happens to the protein molecule when it under- 

 goes oxidization, we would witness a violent explosion, 

 like that of a mass of gunpowder. And the astonishing 

 fact is that this process is actually the same for the living 

 molecule, for exploding gunpowder, and for the fuel 

 which burns in the locomotive boiler. Does this mean 

 that the essential process of what we call life is a chemi- 

 cal one? So it would seem on the basis of this fact 

 alone, but a conclusion must be deferred until we reach 

 a later point. 



The second kind of substance which we find in pro- 

 toplasm is the carbohydrate. A typical member of 

 this group is common sugar, CgH^jOg ; another sugar has 



