978 NUTRITION AND HEAT REGULATION. 



evidence to show that the amount of catalase in a tissue or an ani- 

 mal varies directly with the intensity of the processes of oxidation, 

 and. moreover, that in any given tissue, the skeletal muscles, for 

 example, the amount present may be increased by exercise and 

 decreased by inaction or starvation. This evidence would seem 

 to connect the catalase in a direct way with the processes of phys- 

 iological oxidation and show that there is an adaptive reaction 

 by means of which the quantity varies to correspond with the 

 needs of the organism. The oxidations effected by this means 

 are the principal source of the development of heat in the body 

 they are especially exothermic reactions. Many other of the 

 chemical changes of metabolism, such as the hydrdlytic cleavages, 

 liberate but little heat, and others still, such as the syntheses of 

 one kind or another in which there is a union of compounds to 

 form more complex substances, may even be attended by an 

 absorption of heat, that is, a conversion of heat energy to the energy 

 of chemical affinity. The oxidizing reactions constitute, therefore, 

 a large and very characteristic feature of the metabolism of the 

 warm-blooded animals. The heat thus produced by the oxidation 

 of our food material serves to maintain the body temperature at 

 its normal high level, and establishes a temperature environment 

 at which the enzymatic and chemical metabolism of the tissues 

 is at its optimum. 



