84 ORGANISM AND ENVIRONMENT 



Rubner showed that nitrogenous food, fat, and car- 

 bohydrate are substituted for one another as material 

 for oxidation in exact proportion to the energy which 

 they yield in the body. The sum of this energy per 

 unit of body weight remains constant during rest, 

 whether food is given or withheld. Even when loss of 

 heat is prevented as far as possible, the oxidation pro- 

 cesses in the body remain sensibly constant in spite of 

 prolonged deprivation of food. The diminished oxida- 

 tion of nitrogenous material during starvation depends 

 simply on the fact that the body stores its energy- 

 forming material mainly as fat, and consequently uses 

 up mainly fat during starvation. When all the fat 

 is exhausted there is again, before death from starva- 

 tion, a great increase in the oxidation of nitrogenous 

 material. This latter fact adds new emphasis to the 

 persistence of the oxidation processes. 



The internal environment which is maintained so 

 constant is in reality the expression of a balance be- 

 tween activities which disturb and activities which 

 restore it. When we speak of "the function" of an 

 organ and regard this function as what it does to 

 restore the internal environment we are thinking in 

 terms of an imperfect and misleading conception of 

 what that organ is, and what an organism is : for we 

 are thinking of only one side of its activities to the 

 exclusion of others which are just as important. To 

 put this into philosophical language we are thinking 

 abstractly, or regarding only a part of the reality we 

 are dealing with. We can speak more correctly of 



