964 



NUTRITION AND HEAT REGULATION. 



temperature from about 15° C. upward. When outside tem- 

 peratures fall below this point a new method of regulation, the 

 chemical regulation, comes into play and acts upon the side of 

 heat production rather than of heat loss. This mode of heat 

 regulation is considered in the next paragraph. 



Regulation of Heat Production (Chemical Regulation).— Heat 

 production is varied in the body by increasing or decreasing the 

 physiological oxidations. This end is effected in part voluntarily 

 by muscular exercise or by taking food. Muscular contractions 

 are attended by a marked hberation of heat and it is a part of 

 everyone's experience that by work or muscular activity the effect 

 of outside cold may be counteracted. During fasting a certain 

 amount of body material (glycogen, fat, protein) is oxidized and 

 sufficient heat is produced to counterbalance the heat that is lost. 

 If food is taken it will be oxidized, and the supply of body material 

 will be spared. But the digested products of the foodstuffs, espe- 

 cially of the proteins, stimulate the body metabolisms (specific 

 dynamic action, p. 906), and cause an increase in heat production. 

 By this means, therefore, the quantity of heat formed in the body 

 may be raised temporarily above the usual level. Outside cold is 

 most effective in stimulating the appetite and thus leading us to 

 increase the diet. In this, as in other respects, the appetite serves 

 to control the amount of food in proportion to the needs of the 

 body. The purely involuntary control of heat production con- 

 sists of an involuntary reflex upon , muscular metabolism. Rub- 

 ner has shown by calorimetric experiments upon animals that 

 although the body temperature, as we know, may remain con- 

 stant when the outside temperature is changed, the heat pro- 

 duction is increased as the outside temperature is lowered. This 

 fact is well shown by the following table, compiled by Rubner, 

 from experiments made upon a fasting guinea-pig:* 



From 0° to about 35° C. the animal's body temperature remained 



practically constant, but the oxidations at the lower temperature 



were over twice the amount of those at the higher temperature. 



* Taken from Lusk, Loc. cit. 



