Chap. XVIII.] BODILY HEAT. 221 



packs ; liow we recognize tlie first signs of restored function — 

 the moist, warm sweat in tlie palm of the hand — as a pretty 

 sure sign tliat the fever is " broken." If a very higli tempera- 

 ture persists for any length of time, the metabolism of the tis- 

 sues goes on at such a rapid rate that the capital of the body 

 is soon exhausted. Every organ works with feverish activity, 

 the heart and lungs increase their action, the pulse and respira- 

 tion become more and more hurried, and consequently more and 

 more feeble, until finally, unless relief is obtained, the patient 

 dies of exhaustion. 



In exposure to variations of external temperature the skin is 

 also the chief agent in regulating the heat of the body. Expos- 

 ure to cold stimulates the nerve fibres which bring about reflexly 

 a constriction of the blood-vessels. As a result, less blood is sent 

 to the surface to be cooled, and the average blood-temperature 

 is maintained. On the other hand, exposure to warmth causes 

 reflexly a dilatation of the cutaneous blood-vessels, and more 

 blood is sent to the surface to be cooled. Briefly, when the 

 external temperature is high, the cutaneous blood-vessels dilate, 

 and the sweat is also usually poured out upon the surface of 

 the skin ; when the external temperature is low, the cutaneous 

 blood-vessels contract, and the skin usually remains dry. 



By clothing we can aid the functions of the skin and the 

 maintenance of heat ; though, of course, clothes are not in them- 

 selves sources of heat. The object of clothing is, in winter, to 

 prevent conduction and radiation of heat from the skin, and, in 

 summer, to promote it. Of the materials used for clothes, linen 

 is a good conductor ; calico or muslin not quite so good, while 

 wool, silk, and fur are all bad conductors. 



Subnormal temperature. — In some maladies the temperature 

 falls distinctly below the normal. This is no doubt chiefly due 

 to diminished metabolism. In cases of starvation, the fall of 

 temperature is very marked, especially during the last days of 

 life. The diminished activity of the tissues first affects the cen- 

 tral nervous system ; the patient becomes languid and drowsy, 

 and finally unconscious ; the heart beats more and more feebly, 

 the breath comes more and more slowly, and the sleep of uncon- 

 sciousness passes insensibly into the sleep of death. 



