356 Professor Helmholtz on the Law of the [April 12, 



Now these measurements give us another analogy. We see that in 

 ascending a mountain we produce heat and mechanical work, and that 

 the fifth part of the equivalent of the work which is produced by the 

 chemical process is really gained as mechanical work. Now if we take 

 our steam-engine, or a hot-air engine, or any other engine which is 

 driven by heat in such a way that one body is heated and expands, 

 and by the expansion other bodies are moved, — I say, if we take any 

 thermo-dynamic engine, we find that the greatest amount of mechanical 

 work which can be gained by chemical decomposition or chemical com- 

 bination is only an eighth part of the equivalent of the chemical force, 

 and seven-eighths of the whole are lost in the form of heat ; and this 

 amount of mechanical work can only be gained if we have the greatest 

 difference of temperature which can be produced in such a machine. 

 In the living body we have no great difference of temperature ; and in 

 the living body the amount of mechanical work which could be gained 

 if the living body were a thermo-dynamic engine, like the steam-engine 

 or the hot-air engine, would be much smaller than one-eighth. Really, 

 we find from the great amount of work done, that the liuman body is 

 in this way a better machine than the steam-engine, only its fuel is 

 more expensive than the fuel of steam-engines. 



There is another machine which changes chemical force into 

 mechanical power ; that is, the magneto-electric machine. By these 

 magneto-electric machines a greater amount of electrical power can be 

 changed into mechanical work than in our artificial thermo-dynamic 

 machines. "VVe produce an electric current by dissolving zinc in 

 sulphuric acid, and liberating another oxidizable matter. Generally it 

 is only the difference of the attraction of zinc for oxygen compared 

 with the attraction of copper or nitrous acid for oxygen. In the 

 human body we burn substances which contain carbon and hydrogen, 

 and therefore the whole amount of attraction of carbon and hydrogen 

 for oxygen is put into action to move the machine ; and in this way 

 the power of the living body is greater and more advantageous than 

 the power of the magneto-electric machine. 



Let us now consider what consequences must be drawn when we 

 find that the laws of animal life agree with the law of the conservation 

 of force, at least as far as we can judge at present regarding this sub- 

 ject. As yet we cannot prove that the work produced by living bodies 

 is an exact equivalent of the chemical forces which have been set into 

 action. It is not yet possible to determine the exact value of either 

 of these quantities so accurately as will be done ultimately ; but we 

 may hope that at no distant time it may be possible to determine 

 this with greater accuracy. There is no difficulty opposed to this task. 

 Even at present I think we may consider it as extremely probable that 

 the law of the conservation of force holds good for living bodies. 



Now we may ask, what follows from this fact as regards the 

 nature of the forces which act in the living body ? 



The majority of the physiologists in the last century, and in the 

 beginning of this century, were of opinion that the processes in living 



