INFLUENCE OF NERVOUS SYSTEM ON HEAT PRODUCTION 467 



HEAT PRODUCED PER KILO PER HOUR. (MuNK.) 



Man i . o calories. 



Dog (large) 1.7 calories. 



Dog (small) 3.8 calories. 



Guinea-pig 7.5 calories. 



Rat 11.3 calories. 



Mouse 19.0 calories. 



Sparrow 35-5 calories. 



The ingestion of foods increases the metabolism of the tissues. As one 

 would expect, the rate of heat production is found by experiment upon the 

 dog to be increased after a meal, reaching its height about six hours after a 

 meal. 



It has also been experimentally ascertained that the rate of heat produc- 

 tion varies with the kind of food taken: for example, if sugar be added to the 

 meal of meat given to the dog, the height of maximum production is reached. 

 It is often said that the various nations have found by experience what food 

 is most suitable for the climate in which they live, and that such experience 

 can be trusted to regulate the quantity consumed. Although there have 

 been no very conclusive experiments to prove the view, yet it is a matter of 

 general observation that in northern climates and in colder seasons the quan- 

 tity of food taken is greater than in warmer climates or in warmer seasons. 

 Moreover, the kind of food is different. For example, persons living in the 

 colder climates require much fat in order to produce the requisite amount of 

 heat. 



Influence of the Nervous System on Heat Production. The influence 

 of the nervous system in modifying the production of heat must be very 

 important, as upon the nervous influence depends the amount of the metab- 

 olism of the tissues. The experiments and observations which best illus- 

 trate it are those showing, first, that, when the supply of nerves to a part is 

 cut off, the temperature of that part falls below its ordinary degree after a 

 time; and, second, that when there is severe injury to or removal of the 

 nervous centers the temperature of the body rapidly falls, even though arti- 

 ficial respiration be performed, the circulation maintained, and to all appear- 

 ance the ordinary conditions for chemical changes in the body be completely 

 maintained. 



There is a heat-regulating nervous apparatus closely comparable to that 

 which regulates the secretion of saliva or of sweat, by means of which the pro- 

 duction of heat in the warm-blooded animals is increased or diminished, as 

 occasion requires. This apparatus probably consists of a center or centers 

 in the brain which may be reflexly stimulated, as, for example, by impulses 

 from the skin, and which act through special nerves supplied to the various 

 tissues. The evidence upon which the existence of this regulating appara- 

 tus is assumed is the marked effect in the increase of the oxygen consumed by 



