956 



NUTRITION AND HEAT REGULATION. 



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, especially of the proteins, 

 stimulate the body metabolisms (specific dynamic action, p. 905), 

 and cause an increase in heat production. By this means, there- 

 fore, the quantity of heat formed in the body may be raised tem- 

 porarily above the usual level. In normal individuals this regula- 

 tion is not, strictly speaking, voluntary. Outside cold is most 

 effective in stimulating the appetite and thus leading us to in- 

 crease 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 and 

 possibly in the existence of a special set of heat centers and heat 

 nerves. With regard to the first effect we have the striking 

 experiments quoted by Pfliiger,* according to which a rabbit 

 paralyzed by large doses of curare is no longer able to maintain 

 its body temperature when the outside temperature is changed. 

 The rabbit behaves, in fact, like a cold-blooded animal. In 

 the calorimeter it shows a marked loss of heat production, and its 

 temperature may be made to go up and down with the outside 

 temperature. The same result may be obtained by section of all 

 the motor nerves, that is, section of the spinal cord in the upper 

 cervical region. Rubner has shown by calorimetric experiments 

 upon animals that although the body temperature, as we know, 

 may remain constant when the outside temperature is changed, 

 the heat production 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 :f 



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

 practically constant, but the oxidations at the lower temperature 



* Pfltiger, "Archiv f. die gesammte Physiologic," 18, 255, 1878. 

 t Taken from Lusk, loc. cit. 



