22 THE STORY OF LIFE'S MECHANISM. 



THE MECHANICAL NATURE OF LIVING 

 ORGANISMS. 



This new attitude forced many new problems 

 to the front. Foremost among them and funda- 

 mental to them all were the questions as to the 

 mechanical nature of living organisms. The law 

 of the correlation of force told that the various 

 forms of energy which appear around us light, 

 heat, electricity, etc. are all parts of one common 

 store of energy and convertible into each other. 

 The question whether vital energy is in like 

 manner correlated with other forms of energy was 

 now extremely significant. Living forces had been 

 considered as standing apart from the rest of 

 nature. Vital force, or vitality, had been thought 

 of as something distinct in itself ; and that there 

 was any measurable relation between the powers 

 of the living organism and the forces of heat and 

 chemical affinity was of course unthinkable be- 

 fore the formulation of the doctrine of the cor- 

 relation of forces. But as soon as that doctrine 

 was understood it began to appear at once that, 

 to a certain extent at least, the living body might 

 .be compared to a machine whose function is 

 simply to convert one kind of energy into 

 another. A steam engine is fed with fuel. In 

 that fuel is a store of energy deposited there 

 perhaps centuries ago. The rays of the sun 

 shining on the world in earlier ages, were seized 

 upon by the growing plants and stored away in 

 a potential form in the wood which later became 

 coal. This coal is placed in the furnace of the 

 steam engine and is broken to pieces so that it 



