IS THE ORGANISM A MECHANISM? 659 



dioxide into carbohydrate. Further, precisely the same synthesis 

 is effected by certain species of bacteria. Nitrifying organisms 

 can form carbohydrate and proteid from a medium containing 

 an ammonia salt, water, atmospheric carbon dioxide, and traces 

 of essential mineral substances, in the absence of light radiation. 

 A general theory of organic syntheses must also include these 

 transformations, and must not regard as indispensable a source 

 of available energy in the form of radiation. 



Let us consider the system, water, carbon dioxide, and 

 radiation as an inorganic one. If it can undergo an irreversible 

 change it will do so, when it will attain a condition of stability. 

 If it cannot undergo an irreversible change it will remain stable. 

 It does not, of course, change; that is, of itself. The system 

 carbon dioxide, water, and light radiation is not susceptible 

 of transformation into the system carbohydrate. Neither will 

 water and carbon dioxide undergo spontaneous change to form 

 acetylene. But water can be decomposed so as to obtain 

 hydrogen and oxygen, and carbon dioxide can be decomposed 

 so as to obtain elementary carbon. Acetylene can then be 

 synthesised from its elements. But obviously the synthesis is 

 only possible when we couple the systems, incapable of them- 

 selves of further change, with other systems which do undergo 

 change, in the course of which available energy is evolved. 

 That is to say, we can reverse otherwise irreversible energy- 

 changes if to the system which has attained stability we can 

 couple a compensatory energy-transformation. Assuming, then, 

 that the formation of sugar in the green plant is a physico- 

 chemical reaction dependent on the transformation of the energy 

 of radiation, we arrive at the conclusion that the living plant- 

 cells themselves are not part of the physico-chemical system in 

 which the potential chemical energy of sugar is being 

 accumulated, but they are the agency which effects the com- 

 pensatory energy-transformation. 



Reverting now to the essential distinction between animal 

 and plant we recall that the former is a physico-chemical system, 

 in which potential energy passes into kinetic energy ; while in 

 the latter there is an accumulation of potential energy. In 

 inorganic systems in which potential passes into kinetic energy 

 the tendency is always the same, that is, the final form of the 

 transforming energy is low-temperature heat, which becoming 



