270 



VETERINARY PHYSIOLOGY 



duction may be insufficient to balance beat loss, and the 

 body temperature begins to fall. When this occurs the rate 

 of metabolism and consequently of heat production is in- 

 creased either by increased muscle tonus or by muscular 

 exercise. This increased muscular activity may consist of 



in degrees 

 centigrade 



10 



So 



60 



h.b 



iSO C 



Fig. 137. — To show the physical and the chemical regulation of temperature. 

 Note that roughly between 20° and 40° C. the regulation is by changes 

 in the loss of heat, and that below 20° C. increased heat production 

 occurs. Above 40° C. a hyperthermal increase of heat production occurs. 



voluntary movements, or, if these be prevented, by a shivering 

 fit which is simply a reflex, involuntarily bringing into action 

 a large number of muscles. 



The voluntary movements for heat production are seen 

 in the " freshness " of a horse brought out of a warm stable 

 into a cold atmosphere. A shivering fit is often seen in the 

 horse after drinking a large quantity of cold water, which 



