170 PRACTICAL PHYSIOLOGY 



coat, 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 progres- 

 sive 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 and 

 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 

 displacement 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 tem- 

 perature of the body. The same effect follows curarisation ; sec- 

 tion 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." 



CHAPTER XXXV 

 THE FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM 



The Action of Strychnine and of Chloroform. The cerebrum of a 

 frog is destroyed by means of Spencer Wells' forceps, and then 

 under the skin of the back are injected 10 minims of a saturated 

 solution of strychnine (1 in 6,700). In two or three minutes it will 

 be noticed that the frog cannot readily recover its hind legs after 

 a jump, and soon the reflex excitability of the spinal cord is so 

 augmented that a slight touch or puff of wind upon the skin causes 

 a general spasm of the muscles. Convulsions quickly follow, and 

 the rigid body of the frog rests on the mouth and toes, a position 

 known as emprosihotonus. This attitude is due to the different 

 strength of the various muscles ; all are thrown into contraction, 



