QUESTIONS AND ANSWERS 129 



Explain why the temperature does not rise unduly as a result of severe 

 exercise. 



Because the heat-regulating mechanism causes the excess of heat 

 to be lost through radiation, sweating, etc., and thus a balance is 

 maintained. 



Mention the causes of the variations in the average temperature of the 

 horse and of the dog. 



A rise in temperature may be due to a contraction of the capil- 

 laries in the skin, following a cooling of the exterior, thus sending 

 more blood to the deeper internal parts. Exercise and oxidation of 

 food increase the body heat, therefore there is a daily variation corre- 

 sponding to periods of activity and rest. When the peripheral 

 vessels dilate, a greater radiation occurs and the internal tempera- 

 ture falls. The body temperature is lowest in the early morning 

 when the vital processes are at lowest ebb. 



Describe the chief factors in the regulation of the temperature of the 

 body. 



The heat centres in the brain preside over the heat-regulating 

 mechanism. Heat loss occurs through radiation and conduction, 

 evaporation of sweat, evaporation from the mouth and nostrils, 

 vaporizing of water from the lungs, warming of inspired air, feces 

 and urine. Heat production occurs through oxidation of tissues, 

 glandular activity, and muscular contraction and tension. 



What is a calorie or heat unit? 



A large calorie is the amotmt of heat needed to raise one kilo- 

 gramme of water from 0° to 1° C A small calorie is the amount 

 of heat needed to raise one gramme of water 1° C. in temperature. 

 (A horse produces 2.1 large calories per hour for every 2.2 pounds 

 of body weight and it is estimated that a 1100 pound horse loses 

 20,684 large calories per diem when at rest, 24,500 at moderate 

 work and 37,200 at hard work.) 



What tissues produce the greatest amount of heat? 



The skeletal muscles; four-fifths of the daily heat production 

 originating in them. 



Compare the natural means by which the body of the horse is cooled 



in summer with the means by which the body of the dog is 



cooled. Explain. 



The horse loses heat to a great extent by the evaporation of 



perspiration from the skin. The dog sweats but little and that only 



on the foot-pads, but by panting, the mouth cavity and respiratory 



passages are supplied with a rapidly changing current of air. This 



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