160 REGULATION OF HEAT PRODUCTION. 



off. But this is not the only fact to be taken into considera- 

 tion. It seems highly probable that there is a nerve center 

 controlling the amount of heat produced. We know that the 

 heat is produced by oxidations in the tissues. Now, the effect 

 of cold is to increase the amount of oxygen consumed and 

 the amount of carbon dioxid given off, showing that more 

 heat has actually been generated. 



We call certain animals " cold-blooded." But the fact that 

 they are less warm than birds and mammals is not so signifi- 

 cant as the fact that these cold-blooded animals, instead of 

 maintaining a constant temperature, vary greatly in tempera- 

 ture, being ordinarily only a little warmer than the surround- 

 ing air or water. Now, when these creatures are cold, they 

 take less oxygen and give off less carbon dioxid. 



Aside from these natural methods of keeping the tempera- 

 ture of the body uniform, we aid the process in more or less 

 artificial ways. 



Regulation of Bodily Temperature by Food and 

 Clothing. When subject to the influence of cold we choose 

 more heat-producing foods, as fatty foodstuffs ; we take more 

 vigorous exercise ; we put on more clothing, and especially of 

 the non-conducting kinds, woolens. In warmer weather we 

 eat less fatty matter, wear less clothing, and are less disposed 

 to exercise actively ; we fan ourselves to help get rid of heat ; 

 we take ices and cold drinks. For most persons it seems 

 better to wear woolen most of the time, as even in summer 

 we are subject to sudden changes in the air, and with such 

 covering one is less likely to take cold. 



In getting the clothing wet, the greater loss of heat is not 

 from the coolness of the water, but the loss of heat in evapo- 

 rating the water from the clothing ; and this goes on for a long 

 time. Of course it is very desirable to put on dry clothing as 

 soon as possible ; but a person in good health is not very 



