EXTENSION OF EVOLUTIONARY THEORIES 35 1 



merely implies that our present means and knowledge 

 do not sufifice for constructing a mechanical explanation ; 

 it does not follow that there will always be insuperable 

 difficulties in the way of it. On the contrary, we have 

 already good reason to say that a mechanical explanation 

 of life is possible. We have already given a physico- 

 chemical analysis of some aspects of the vital processes 

 which were formerly attributed to a vital force. There 

 are certain substances that are only found in the living 

 body, yet have been artificially produced by chemistry. 

 Uric acid is the best known of these. 



The Vitalists reply that we must put outside the 

 category of real vital phenomena all aspects of the vital 

 processes that can be conceived as purely mechanical. 

 But it has been rightly pointed out to them that the 

 problem before us is ; Can the vital processes be 

 conceived as physico-chemical ? If the Vitalists say it 

 is the characteristic of vital phenomena to be incapable 

 of being conceived as physico-chemical, they are begging 

 the whole question. 



I have already said that we do not know under what 

 conditions the chief elements of the organic body, the 

 albuminoids, are produced. Living albumen is still an 

 unsolved problem for us. Hence our knowledge of the 

 living substance is as yet much too scanty for us to 

 construct successfully a mechanical explanation of the 

 vital processes. 



It has been established by careful research that the 

 same amount of force is used up by an adult organism 

 in its vital activity as is taken into it with its food. 

 Hence all the actions of the body are exactly 



