THE LIVING SUBSTANCE. 



139 



by external environment, which has been most plastic in its 

 devices and activities, is that which is perpetuated. And its 

 activities are developed by use along these lines. This presents 

 a new aspect of natural selection. It is indeed upon the selec- 

 tive power of the substance as such and as machine that the 

 natural selection of Darwin must act. It must always be acces- 

 sory after the act rather than an agent in the act, and even 

 habit, individual or inherited, cannot be excepted. Through 

 grasp of this basic fact of substance life, namely, selection of 

 its own specific environment, individual, race and species habits 

 are brought into a more unified and intelligible relation. 



The "struggle for existence" remains a struggle for food, 

 using the word in its broadest sense. All struggles of the 

 substance either as such or as organism for place and vantage 

 in external environment as well as for the actual substances it 

 holds, are to this end. Air, light, space, with more subtle con- 

 ditions hardly yet understood in some cases, are also demanded 

 by the organism because the substance as such requires these 

 for its activities and internal arrangements. In the battle for 

 these, such docile ingenuity and plastic contrivance are displayed 

 by the substance, as more and more amaze research workers. 

 The tendency of evolution seems to have followed lines of 

 strengthening and conserving this aim and need of the Sub- 

 stance, — to control its own environment. 



[138] Now food for the organism has commonly been taken 

 to mean actual increment for it, either as new living substance 

 or to replace portions of this which have suffered dissolution 

 supposed to be a necessary result of characteristic activities. 

 Certain remarkable correlations between the waste product, 

 loss of mass or weight in the organism, the amount of energy 

 displayed and the heat generating properties of the food taken 

 in ; have formed the basis for a belief that food is used to repair 

 waste of the actual living substance or to construct new 

 quantities of this. The facts as to structure given here, make 

 it quite possible and even plausible to suppose that we should 

 not with certainty predicate this correlation between chemical 

 and physical expenditure or supply and physiological activity, 

 as meaning destruction or repair of the actual living substance. 



