Problems of Organic Adaptation 



fact that many vital processes may be explained in terms 

 of chemistry and physics. Even the strongest adherents of 

 vitalism must recognize the fact that neither matter nor 

 energy is created or destroyed in an organism, but that 

 these merely undergo transformations (metabolism). All 

 energy of an animal comes from its food just as the energy 

 of an engine conies from its fuel; the vital machine is as 

 dependent upon food as the engine is on fuel. However, 

 only the first and last steps in constructive and destructive 

 metabolism are known; the middle step, assimilation, is 

 still a good deal of a mystery, but it is probably a chemical 

 process in which each of the many kinds and varieties of 

 protoplasm is built up out of the common nutrient materials 

 through the action of specific enzymes. 



The properties of reproduction, irritability, and adapta- 

 bility are more distinctive of living things and are more 

 difficult to explain on a physico-chemical basis than is me- 

 tabolism. Certain analogies to each of these processes are 

 found in the inorganic world, and certain steps in each of 

 them are plainly physico-chemical in origin, but it must be 

 admitted that there is left a large residuum which cannot 

 at present be explained on mechanistic grounds. However, 

 much progress is being made in this direction, and this justi- 

 fies the hope that many more, if not all, vital processes will 

 ultimately be explained in this way; certainly there seems to 

 be no justification for abandoning the search for mechanistic 

 explanations at a time when they are being found as never 

 before, nor for turning at once from a mechanistic philoso- 

 phy of life to obscurantism or mysticism. For although 

 mechanism may not in the last analysis explain vital phe- 

 nomena, or anything else for that matter, it is evident that 

 very much of a mechanistic nature remains to be discovered 

 in organisms, and the great advantage of mechanism over 



