REGULATION OF ENVIRONMENT 83 



environment we find that they are no less persistent 

 than the activities which maintain its constancy. The 

 muscles still continue to consume oxygen and form 

 heat, even though they are for the time at rest, and 

 though all loss of heat from them is prevented. The 

 kidneys still absorb oxygen when they are not secret- 

 ing. In a sense, too, they are still secreting, even when 

 there is no external sign of secretion, for the absence 

 of external secretion is only the expression of an equal 

 balance between constant intake and constant output 

 of material. When the muscles and sense-organs are 

 not at work on the getting of food, or in other con- 

 servative processes, they seem to employ themselves 

 otherwise for instance in what we know as play. 



No physiological facts are more significant than 

 those relating to the persistence of the fundamental 

 metabolic phenomena. In Liebig's time it was observed 

 that the excretion of urea rises and falls with the 

 amount of nitrogenous food consumed, although dur- 

 ing starvation there is still a certain minimum excre- 

 tion of urea. This was interpreted as signifying that 

 all superfluous nitrogenous food simply falls a prey to 

 oxygen, and is wasted. When, however, the facts 

 were further investigated it was found that within 

 wide limits the oxidation in the body does not increase 

 or diminish with increase or diminution of the nitrog- 

 enous food consumed. Even after long starvation 

 the oxygen consumption per unit of body weight is 

 practically undiminished during rest. When more 

 nitrogenous food is consumed in the body and oxidised 

 to urea, less fat or carbohydrate is consumed. 



