202 PRACTICAL PHYSIOLOGY 



radiation, convection and conduction. It may be readily taken by a 

 mercurial thermometer with a flat bulb. A difference of 10 C. may 

 be observed in the temperature of the skin of the hand in summer and 

 winter; in warm weather the cutaneous blood-vessels are dilated, in 

 cold weather they are contracted. The temperature, however, of those 

 parts of the body which are constantly covered with clothing shows 

 little change. 



Clothes diminish the loss of heat from the body by enclosing layers 

 of stationary air, so that the surface of the trunk and limbs is sur- 

 rounded by a layer of air nearly as warm as the skin. 



EXPERIMENT. Take the temperature of the skin of the hand and 

 compare it with that of the chest or abdomen. Compare also the 

 temperatures recorded in the air space between the coat and waistcoat, 

 between the waistcoat and shirt, between the shirt and vest, and lastly 

 between the vest and skin. In cold weather it will be found that the 

 temperature of these strata of air shows a progressive rise, so that the 

 air between the vest and the skin is almost as warm as the skin itself. 



The heat lost from the skin depends upon the temperature arid 

 moisture of the air. The temperature recorded by the wet-bulb 

 thermometer is the important factor it can be taken by wrapping 

 some moist cotton round the bulb of a thermometer and waving it in 

 the air, but always keeping it upright, so that no mechanical displace- 

 ment of the mercury may occur. 



Sweat. The discharge of sweat is under the control of the nervous 

 system, and a simple experiment will prove the existence of sudorific 

 nerves. A cat is killed by an overdose of ether or chloroform. The 

 sciatic nerve is exposed and stimulated by a strong faradic current ; 

 after a short delay beads of sweat will be seen on the pads of the foot. 

 The pad of the opposite leg will serve as a contrast. 



Effect of Anaesthesia on the Temperature of the Body. DEMON- 

 STRATION. A small mammal is anaesthetised with chloral or urethane 

 after its rectal temperature has been taken. If the animal be now laid 

 on a table with its limbs spread out, and be exposed to the ordinary 

 temperature of a room, its temperature will fall. This is chiefly due to 

 the cessation of muscular movement and the paralysis of the central 

 nervous system, which regulates the temperature of the body. The 

 same effect follows eurarisation ; section of the spinal cord in the lower 

 cervical region ; and the administration of large doses of alcohol. 



Anaesthetised patients must be protected from cold. Drunkards 

 who fall asleep on the roadside on a winter's night are easily " frozen 

 to death." 



