82 Feeds and Feeding. 



different parts of the body is more or less equalized, chiefly by the 

 circulation of the blood. Generally, however, the temperature of 

 the body in its different parts varies somewhat according to the 

 activities of the parts. 



An increase in the amount of work performed will result in an 

 increased production of heat within the body. All the heat gen- 

 erated within the animal body is, as it were, a by-product of inter- 

 nal or external work, but is available for the maintenance of the 

 body temperature. Some eminent physiologists hold that the 

 amount of heat evolved in the production of internal and external 

 work is sufficient to warm the body under all conditions, and that 

 there is no production of heat in the body to simply keep it warm. 

 Convincing proof of this theory is lacking, and it seems reasonable 

 to believe, as do many eminent scientists, that, at least when there 

 is an unusual demand for heat, caused by a low external tempera- 

 ture, the heat generated as a result of internal and external work 

 is not sufficient, and food or body tissue is burned up for the direct 

 and sole purpose of warming the body. 



105. Heat regulation. As heat is constantly being produced in 

 the body, if means were not provided for its escape and for the regu- 

 lation of body temperature, the temperature would steadily rise 

 until the animal was destroyed. It has been shown that the horse 

 at rest produces sufficient heat in two days to raise the temperature 

 of the body to the boiling point. 1 However, the body possesses 

 means for controlling both the production and the loss of heat, this 

 twofold heat regulation being under the control of the nervous 

 system. 



The production of heat in the body is regulated by increasing or 

 decreasing the oxidations taking place therein, this regulation be- 

 ing known as chemical regulation. Heat production is controlled 

 more or less voluntarily by regulating the exercise taken and the 

 amount of food consumed. The degree of external heat or cold also 

 causes an involuntary rise or fall in the amount of heat produced 

 in the body. For instance, as a result of nervous stimuli more fuel 

 is burned in the body during extreme cold than normally. 



The second means of heat regulation, called physical regulation, 

 is by controlling the amount of heat lost from the body. This is 

 accomplished in part by varying the distribution of the blood on the 

 surface of the body, and thus controlling the amount of heat lost 

 from the skin by radiation and conduction. The loss of heat is 



1 Smith, Man. of Vet. Physiol., p. 343. 



