THE ORGANISM AS A MECHANISM 75 



it should be noted that in this fall of potential is a 

 degradation of chemical energy. Compounds, carbon 

 dioxide, water, and nitrate are produced which are 

 chemically inert. It is no use to say that carbon 

 dioxide may react with (say) glowing magnesium, 

 water with metallic sodium, and nitrate with (say) 

 glowing carbon. A condition of chemical equilibrium 

 would result from purely inorganic becoming on 

 our earth in which there was no metallic sodium or 

 magnesium or incandescent carbon ; in which the 

 metals would become inert oxides, and the carbon 

 would become dioxide. The formation of these com- 

 pounds represents a limit to energy-transformations. 

 Note also that all these energy-transformations are 

 conservative ; the total quantity remains unchanged 

 throughout, and is the same at the end as at 

 the beginning. But entropy has been augmented : 

 unavailable energy has increased at the expense of 

 available energy. 



Consider now the indirect, or reversed, Carnot cycle. 

 We begin with the inert matter, resulting from the 

 metabolism of the animal, carbon dioxide, water, 

 nitrate, and a few more mineral substances. We have 

 the energy of solar radiation. By virtue of the living 

 chlorophyll plastid in the cells of the green plant, this 

 solar radiation uses the carbon dioxide and water as 

 raw materials in the elaboration of starch. At the same 

 time it absorbs nitrate, with some other inert mineral 

 substances from the soil, and takes these into its 

 tissues. The starch formed in the chlorophyll is 

 converted into soluble sugar, which circulates through 

 the vessels of the plant and is associated with the 

 nitrogenous salt in the elaboration of proteid. Proteid, 

 oils, fats and resins, and to a greater extent carbo- 

 hydrates, are thus built up by the plant and accumulate, 



