DRUGS ACTING ON THE NERVOUS SYSTEM 39 



functions of the brain in the inverse order of their evolu- 

 tionary development. The centres last to be acquired are 

 the first to be paralyzed (cerebral centres) ; while those of 

 earliest origin (the respiratory, vagus and vasomotor centres) 

 are last to succumb to the action of cerebral depressants. 

 The cerebral depressants are used mostly to relieve pain, 

 when they are called anodynes.* Pain is due to irritation of 

 any sensory nerve, or the sensory tract in the spinal cord, 

 or of the sensory centres in the brain. Pain may be relieved 

 by paralyzing any portion of this path and destroying 

 connection with the perceptive centres in the brain. 



(1) Anodynes^ by reason of their action on the brain. 



Opium Chloral 



Morphine Cannabis Indica 



Codeine Gelsemium 



Alcohol Bromides 

 Anaesthetics 



(2) Narcotics. — This term is a broad and somewhat 

 inclusive one. Narcotics embrace drugs which depress the 

 brain and cause sleep (hypnotics or soporifics) and stupor 

 (some anodynes and anaesthetics), and finally paralyze the 

 respiratory and circulatory functions. The following may 

 be included in this group : 



Opium Cannabis Indica 



Alcohol Belladonna 



Anaesthetics Stramonium 



Chloral Hyoscyamus 



(a) Hypnotics or Soporifics (drugs causing sleep). 



Opium Paraldehyde 



Morphine Urethrane 



Chloral Sulphonal 



Bromides Trional 

 Cannabis Indica 



Of little import- 

 ance in Veterin- 

 ary practice 



Uses. — Hypnotics are of not much value in Veterinary 

 medicine by simply promoting sleep. Their general sedative 

 and anodyne actions are utilized in relieving motor excite- 

 ment (spasms), or sensory excitement (pain). 



*0r Analgesics. 



