THE FASTING KAT ABOLISH 265 



the escape of heat from the body by increasing the conducting power 

 of the clothing, hair or fur, so that a damp cold is more severe than 

 a dry cold. The direct rays of the sun may impart a considerable 

 amount of heat to the body, thus moderating the effects of low tem- 

 peratures and, on the other hand, increasing those of high tempera- 

 tures. To be strictly accurate, then, one should speak of a critical 

 thermal environment of the animal rather than simply of a critical 

 temperature. 



356. Influence on katabolism. It is apparent from the 

 foregoing facts that the energy katabolism of the fasting animal 

 is affected by the external temperature and other thermal con- 

 ditions to a considerably less extent than has been frequently 

 imagined. It is by no means true that every fall in external 

 temperature results in an increased katabolism in the animal 

 for the sake of heat production, for if this were the case the con- 

 verse would also be true, viz., that every rise in the external 

 temperature would cause a corresponding decrease in the katab- 

 olism, so that finally, when the external temperature was 

 equivalent to that of the body, the katabolism would be reduced 

 to zero ; that is, we should have life without katabolism, which 

 is a contradiction in terms. 



The fact that the heat production of an animal reaches a 

 minimum at the critical temperature and that above that point 

 it either remains unchanged or increases slightly shows that its 

 extent is not determined by the needs of the organism for heat 

 as such, since these diminish as the temperature rises. As a 

 matter of fact, the production of heat in the body is not the 

 purpose of katabolism but merely an incident of it. Heat is 

 the form which the chemical energy of the katabolized material 

 takes after it has served its purposes in the vital processes, and 

 the nearly constant heat production above the critical tem- 

 perature is simply due to the fact that the quantity of energy 

 required for the internal work of the body is approximately 

 constant and cannot be reduced simply by raising the external 

 temperature. Heat is essentially an excretum to be gotten rid 

 of. Incidentally, in warm-blooded animals, it serves also to 

 maintain the body temperature necessary for the normal per- 

 formance of the vital functions, but above the critical tempera- 

 ture there is a surplus over the amount required for this 

 purpose which is disposed of by the processes of physical regu- 



