830 NUTRITION AND HEAT REGULATION. 



reflex in this case may be regarded possibly as an inhibition of the 

 vasoconstrictor center through the warm nerves of the skin. Sub- 

 stances, such as alcohol, which cause a dilatation of the skin ves- 

 sels also increase the loss of body heat, in some cases to a sufficient 

 extent to lower the body temperature. To a smaller extent our 

 heat loss is controlled through an acceleration of the breathing 

 movements. The greatly increased respirations in muscular ac- 

 tivity must aid somewhat in eliminating the excess of heat produced, 

 although this factor must be much less important than the sweating 

 and the flushing of the skin which are produced reflexly during 

 muscular work. In some of the lower animals the dog, for in- 

 stance in which the sweat nerves are absent over most of the body 

 and in which the coat of hair interferes with the free loss by 

 radiation, it is found that the loss through the respiratory channel is 

 relatively more important. The panting of the dog is a familiar 

 phenomenon. Richet has studied this reflex upon dogs and has 

 designated the greatly accelerated breathing in warm weather or 

 after muscular exercise as thermic polypnea (according to Gad, 

 tachypnea). He assumes a special center for the reflex situated in 

 the medulla and acting through the respiratory center. It is a 

 curious fact, as shown by Langlois, that some reptiles exhibit a 

 similar reflex; when their body temperature is raised to 39 C. they 

 show a condition of marked polypnea (rapid breathing) the ap- 

 parent object of which is to augment the loss of heat from the 

 body. 



Regulation of Heat Production. Heat production is varied 

 in the body by increasing or decreasing the physiological oxida- 

 tions. This end is effected in part voluntarily by muscular exercise 

 or by taking more food. Muscular contractions are attended by 

 a marked liberation 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. In the case of food the body burns promptly most 

 of the material of a daily diet. By increasing the diet in cold 

 weather provision is made for the greater supply of heat required. 

 In normal individuals this regulation is not, strictly speaking, 

 voluntary. Outside cold is most effective in stimulating the appe- 

 tite and thus leading us to increase the diet. In this, as in other 

 respects, the appetite serves to control the amount of food in pro- 

 portion to the needs of the body. The purely involuntary control 

 of heat production consists of an involuntary reflex upon muscu- 

 lar 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 main- 

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



