66 THE FITNESS OF THE ENVIRONMENT 



place these are in the main familiar ideas, 

 and if they were altogether conclusive to 

 prove the existence of really significant fitness, 

 if they could be regarded as alone adequate 

 to establish the necessity of putting fitness by 

 the side of adaptation as a coordinate factor 

 in causing the marvels of life, it is hard to be- 

 lieve that they would have been so long neg- 

 lected. In the second place there is nothing 

 comparative about such information. Water 

 is indeed a wonderful substance which fills 

 its place in nature most satisfactorily, but 

 would not another substance do as well ? Is 

 not ammonia, for example, a possible substi- 

 tute ? And are there not many other chemical 

 bodies which might, in a very different world, 

 serve equally useful purposes ? Perhaps, too, 

 the great variety of carbon compounds which 

 are known to the chemist are known only be- 

 cause the vital processes furnish an abundance 

 of material with which to experiment. Is it 

 not possible, therefore, that another element, 

 silicon, for instance, may enter into even 

 greater varieties of compounds ? It is such 

 questions, ever present in the minds of men of 

 science, yet never carefully scrutinized to see 

 if an answer be possible, which, I suspect, have 

 long deflected attention from this subject. 

 Clearly, therefore, it will be necessary to 



