ANIMAL HEAT. 581 



temperature must remain unaltered, and that if the changes in one exceed 

 those in the other the temperature rises or falls, depending upon whether more 

 or less heat is produced than is dissipated. It does not follow that because 

 heat-production is increased the bodily temperature must similarly be affected, 

 since heat-dissipation may be increased to the same extent and thus effect a 

 compensation. Therefore an alteration in heat-production or in heat-dissipation 

 by no means implies that the temperature must be affected. Moreover, when 

 the temperature is increased or diminished the change may be caused by 

 various alterations in the quantities of heat produced or lost, singly or com- 

 bined, and the temperature may remain constant even when both processes are 

 materially affected. Thus, the temperature remains constant when both heat- 

 production and heat-dissipation are normal, and when both are increased or 

 decreased to the same extent. The temperature is increased when heat-pro- 

 duction is normal and heat-dissipation diminished ; when both heat-production 

 and heat-dissipation are diminished, but when heat-production is diminished 

 to a less extent than heat-dissipation ; when heat-production is increased and 

 heat-dissipation remains normal ; when both heat-production and heat-dissipa- 

 tion are increased, but when heat-production is increased to a greater extent 

 than heat-dissipation ; and when heat-production is increased and heat-dissipa- 

 tion is diminished. The temperature is diminished when heat-production is 

 normal and heat-dissipation is increased ; when heat-production is diminished 

 and heat-dissipation remains normal ; when heat-production and heat-dissipa- 

 tion are diminished, but when heat-production is diminished to a greater extent 

 than heat-dissipation ; when heat-production is diminished and heat-dissipa- 

 tion is increased; and when both heat-dissipation and heat-production are 

 increased, but when heat-production is increased to a less extent than heat- 

 dissipation. 



It is generally regarded by clinicians that bodily temperature varies directly 

 with heat -production that is, that a rise means increased production, and a 

 fall diminished production ; but the fallaciousness of such a conclusion must 

 be apparent. It may, however, be accepted as a fact that in fever, as a rule, 

 an increase of bodily temperature is a concomitant of increased heat-produc- 

 tion, and diminished temperature of diminished heat-piroduction ; but it must 

 also be observed that pyrexia, although generally due to increased heat- 

 production, may also be due partly or wholly to diminished heat-dissipation. 

 It is obvious, therefore, that temperature variations simply show that the 

 balance between heat-production and heat-dissipation is disturbed, without 

 positively indicating how the processes of heat-production and heat-dissipation 

 are affected. 



The mechanism concerned in the adjustment of the relations between heat- 

 production and heat-dissipation will be considered under another heading 

 (p. 602). 



B. INCOME AND EXPENDITURE OF HEAT. 



Broadly speaking, the source of animal heat is in tfce potential energy of 

 organic food-stuffs so little relatively being obtained from the heat of warm 



