456 THE HUMAN BODY. 



3. Cold tends to produce involuntary muscular move- 

 ments, and so increased heat production; as chattering 

 of the teeth and shivering. 



4. Cold applied to the skin increases the bodily chemical 

 metamorphoses and so heat production. At least the tem- 

 perature in the armpit rises at first on entering a cold bath, 

 though the heat carried off from the surface soon overbalances 

 its increased production. The phenomenon may, however, 

 be explained in another way, the rise being attributed to a 

 sudden diminution of loss from more exposed parts of the 

 skin, dependent on contraction of the cutaneous arteries. 

 In some cases, however, the temporary rise is accompanied 

 by an increased excretion of carbon dioxide, which would 

 indicate that the surface cooling does really increase the 

 oxidations of the Body. 



5. Certain drugs, as salicylic acid, and perhaps quinine, 

 diminish the heat production of the Body. Their mode of 

 action is still obscure. 



On the whole, however, the direct heat-regulating me- 

 chanisms of the Human Body itself are not very efficient, 

 especially as protections against excessive cooling. Man 

 needs to supplement them by the use of clothing, fuel, and 

 exercise. 



Local Temperatures. Although, by the means above 

 described, a wonderfully uniform bodily temperature is 

 maintained, and by the circulating blood all parts are kept 

 at nearly the same warmth, variations in both respects do 

 occur. The arrangements for equalization are not by any 

 means fully efficient. External parts, as the skin, the lungs 

 (which are really external in the sense of being in contact 

 with the air), the mouth, and the nose chambers, are always 

 cooler than internal; and even all parts of the skin have 

 not the same temperature, such hollows as the armpit being 

 warmer than more exposed regions. On the other hand, 

 a secreting gland or a working muscle becomes warmer, for 

 the time, than the rest of the Body, because more heat is 

 liberated in it than is carried off by the blood flowing 

 through. In such organs the venous blood leaving is warmer 

 than the arterial coming to them; while the reverse is the 



