APPENDIX 333 



being first transformed into the substance of our body. What is 

 lost to the organism as matter is acquired as energy. But we 

 can accept the following statement as an axiom, says the famous 

 physiologist, Claude Bernard : ' every manifestation of activity 

 in a living organism is necessarily connected with the destruction 

 of a part of its matter.' In the organism as well as in an engine 

 a certain proportion of matter burns down, and this is accom- 

 panied either by the manifestation of heat, or by the mechanical 

 work into which this heat is transformed, such as the work of 

 our muscles. According to Frankland, a pound of wheat 

 bread stores up something like 75,000 foot-pounds of potential 

 energy. There is no doubt that an organism, just like an engine, 

 cannot transform into useful work all the energy stored up 

 within it in the form of fuel, i.e. all the potential energy of 

 the oxidisable parts of its food. Physiological experiments 

 prove, however, that in this respect the living organism far 

 outstrips any steam engine. 



We have proceeded so far towards the solution of the question 

 raised above that we already know the kind of energy con- 

 tained in our food : it is the latent energy of its carbon and 

 hydrogen which are always ready to combine with the oxygen 

 of the air. A fresh problem arises at this point in the course 

 of our investigation. Wood burns, animals burn, man burns, 

 everything burns, and yet nothing burns right away. Forests 

 are burnt down, and yet vegetation is not exterminated. Genera- 

 tions pass away, but mankind is always alive. If everything 

 were only to burn away, the surface of the earth would contain 

 neither plants nor animals any longer : there would soon be 

 only carbonic acid and water. 



Evidently another process must also be going on in Nature, 

 a process contrary to combustion, during which the substances 

 entirely burnt down are ' unburnt,' transformed into substances 

 once more capable of burning. The formation of carbonic acid 

 must be accompanied by a reverse process, the decomposition 

 of the carbonic acid produced by universal combustion. 



The first man whose attention was drawn to the logical neces- 

 sity for such a process in Nature was the great chemist Priestley. 

 As a matter of course this idea could not present itself to his 

 mind in the same form, or with the same precision and clearness, 



