No. 502] CHEMICAL MECHANICS IN LIVING PLANT 663 



damental processes of anabolism, katabolism and growth 

 as slow chemical reactions catalytieally accelerated by 

 protoplasm and inevitably accelerated by temperature. 

 This soon follows if we once admit that the atoms and 

 molecules concerned possess the same essential properties 

 during their brief sojourn in the living nexus as they 

 do before and after. 



Perhaps the more real question is rather as to the 

 importance and significance of this point of view. Pro- 

 toplasmic activity might be something so much per se, 

 and the other factors of the nature of stimuli might be 

 superposed so thickly upon that substratum which should 

 be dominated by simple principles of chemical mechanics 

 that for practical purposes the operations of the latter 

 would be so overlaid and masked as to be neglible. A 

 survey of this field, however, seems to show that this is 

 not so, and that the broad action of the law of mass and 

 the acceleration of reaction-velocity by temperature are 

 obviously responsible for wide ranges of phenomena. 



Now the conception at the bottom of these principles 

 is that of reaction-velocity, and the conclusion of the 

 whole matter is that the physiologist must frankly take 

 over from physical chemistry this fundamental concep- 

 tion. 20 Under definite conditions of supply of material 

 and temperature there is a definite reaction-velocity for 

 a given protoplasm, and the main factors that alter the 

 rate of metabolism, viz., heat, nutrition and traces of im- 

 purities are exactly the factors which affect the velocity of 

 reactions in vitro. 



Working on this basis we no longer need the vague un- 

 quantitative terminology of stimulation for the most fun- 

 damental of the observed "responses" to external con- 



