970 



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. 914), 

 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. 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 consists 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 temper- 

 ature 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 low- 

 ered. 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 



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

 t Taken from Lusk, loc. cit. 



