REGULATION OF THE BODY HEAT. 521 



follows a rise of the internal temperature due to increased 

 metabolic activity, such as muscular exercise : a " warm glow " 

 is felt, the skin flushes and perspires, the circulation and respira- 

 tion are increased, and the activity of other metabolic organs, 

 such as the liver, is for the time lowered. The skin is the 

 principal channel of loss of heat in man ; but during and after 

 exertion a large amount of heat must be carried off by respira- 

 tion, which is familiarly known to be the chief means of 

 refrigeration in the dog. 



Conversely, if the temperature of the surface be lowered by 

 cooling of the atmosphere, two reflex effects are at once pro- 

 duced through the nervous system, viz. : (1) diminished loss of 

 heat, by contraction of the vessels of the skin, by arrest of per- 

 spiration, and by reduced activity of the circulation and lungs ; 

 and (2) increased production of heat in the metabolic organs, 

 especially the muscular, digestive, and circulatory. A similar 

 result follows lowering of the internal temperature by diminished 

 metabolism in some of the organs. Thus Quinia and Salicylic 

 Acid, whilst they diminish the amount of the urea and therefore 

 probably of the heat produced in the system, make little or no 

 impression on the temperature of a healthy man, doubtless 

 because the channels of loss are partially closed, and the meta- 

 bolism of certain organs increased, by the regulating me- 

 chanism. 



H. PHARMACODYNAMICS. 



1. Temperature of the External Media. This is completely 

 under our control. The atmosphere is the ordinary external 

 medium of loss or gain of the bodily temperature, and the air of 

 every well-constructed room or ward can be warmed or cooled 

 at pleasure. We may select the climate in various ways, accord- 

 ing to its temperature ; the sub-tropics, such as Madeira, Egypt, 

 and the Riviera, being especially valuable as affording warm 

 climates. When a more rapid and extreme influence of the 

 external temperature is desired, water may be substituted for air, 

 in the form of baths, wet-packs, and sponging. The varieties, 

 action, and uses of water applied in these several ways are 

 described in the next chapter. By means of the prolonged cold 

 bath, at a temperature varying between 32 and 60 Fahr., heat 

 may be readily abstracted from the body ; and the cold wet pack, 

 cold affusion, or sponging a part or the whole of the exposed 

 skin with cold or even tepid water, has a similar effect. These 

 measures are known as external refrigerants. Heat may be 

 locally abstracted by similar means, which will also have a 

 general effect in reducing the temperature of the body. Thus, 

 cold water may be injected into the rectum or vagina ; ice or wet 

 compresses applied to the skin ; ice or cold water swallowed ; or 



