250 THE REGULATION OF TEMPERATURE 



such a mechanism the heat lost would, of course, increase 

 as the external temperature fell. Now physical regula- 

 tion only partially compensates for this, for the heat 

 lost still rises with fall of temperature, but not to the 

 same extent as would occur were the mechanism absent. 

 Physical regulation therefore produces a relative, not an 

 absolute diminution in heat-loss. The amount of heat 

 lost is further diminished by the instinctive act of putting 

 on more clothes, these serving as a means of entanghng 

 a layer of warm air around the body. Radiation of heat 

 is less in the obese than in the thin, the heat of the body 

 being preserved in the former by the subcutaneous fat. 



Chemical Regulation 



The increased heat- production is again a reflex effect. 

 To its occurrence, which can be demonstrated by calori- 

 -^letry, several factors contribute :■ — 



{a) Increased inclination to voluntary activity ; 

 (6) Involuntary movements — shivering ; 

 (c) Increased tonus of the muscles. 



In dogs, when the passage of impulses from brain to 

 muscles is blocked by administration of curare, the animal 

 loses the power of maintaining a constant temperature 

 when the temperature of the environment falls. 



Increased metabolism leads to increased appetite. Food 

 is taken in larger quantity, and when absorbed adds the 

 heat due to its specific dynamic energy (p. 153). Observa- 

 tions on the respiratory quotient show that this approaches 

 unity — proving that the increase in metabohsm chiefly 

 involves the carbohydrates. 



As the surrounding temperature rises, heat-loss in- 

 creases owing to the discarding of clothes, the diminished 

 vaso-constriction and, later, the secretion of sweat. At 

 the same time, heat-production is decreased owing to a 

 progressive disinchnation for activity and a diminished 



