308 FOUNDATIONS OF BIOLOGY 



and carbonic acid, could possess a like number of fit charac- 

 teristics, or in any manner such great fitness to promote com- 

 plexity, durability, and active metabolism in the organic 

 mechanism which we call life." (Henderson.) 



A. ADAPTATIONS TO THE PHYSICAL ENVIRONMENT 



In any consideration of the reciprocal relations which must 

 exist between organisms and their surroundings, of first im- 

 portance is the inconstancy~of the latter. Uncertainty is the 

 one certainty in nature and accordingly the response of living 

 things their adaptability to environmental exigencies 

 is at once the most striking and indispensable adaptation. 



1. Adaptations Essentially Functional 



Although the changes of the environment are almost in- 

 conceivably complex witness the kaleidoscopic series of 

 events exhibited in the hay infusion microcosm there are 

 certain general conditions which every environment must 

 supply, and without which life cannot exist. These are food, 

 including water and oxygen, certain limits of temperature 

 and pressure. 



FOOD. As we know, food represents the stream of matter 

 and energy which is demanded for the metabolic processes 

 of living matter. And each and every element which forms 

 an integral part of protoplasm must be available. Since 

 all protoplasm consists chiefly of a dozen chemical elements, 

 these, of course, must be present; and further, since proto- 

 plasm is a colloidal complex in which water plays a funda- 

 mental role, life processes without water are impossible. 

 But the old adage that what is food for one is another's 

 poison has a broader content than is immediately apparent. 

 Although it is true there are general 'food-elements' which 

 all life demands, it is equally true that the combinations in 



