DEUGS ACTING ON THE NEETOUS SYSTEM 41 



centres, appears, and ushers in the (2) cmcesthetic stage, char- 

 acterized by muscular relaxation and complete abolition of 

 consciousness, sensation and motion. Between these two 

 stages — the stimulant and anaesthetic — there sometimes 

 occurs a transient state in which sensation is lost before 

 consciousness. This has been styled the anodyne stage. 



Finally, the (3) paralytic stage ensues, accompanied by 

 depression and then paralysis of the three great vital 

 medullary centres controlling the circulation and respiration, 

 together with that of the lowest reflex centres, so that invol- 

 untary micturition and defsecation occurs. The animal dies 

 of a combination of vasomotor, heart and respiratory failure. 

 If recovery should follow the paralytic stage, the bodily 

 functions return in the reverse order to that in which they 

 were lost ; i.e., the lower vital functions first appear, followed 

 finally by the higher cerebral functions. 



Uses. — Anaesthetics are employed in surgical operations 

 to prevent pain and struggling ; in, obstetrical operations 

 and in the reduction of fractures, dislocations and hernia, to 

 secure complete muscular relaxation ; to overcome spasms 

 and convulsions resulting from disease or poisons ; to arrest 

 severe pain in colic ; and finally to destroy aged or sick and 

 useless animals. 



For fuller details see Anaesthesia (p. 299). 



(c) Drugs acting on the cortical motor centres of the hrain. 



(1) DRUGS STIMULATING THE MOTOR CENTRES. 



Strychnine Physostigmine 



Atropine 



(2) DRUGS DEPRESSING THE MOTOR CENTRES. 



The Bromides Alcohol 



Chloral Anaesthetics 



The action of drugs on the cerebral cortical centres has 

 been found by comparing the local effect of electrical stim- 

 ulation before and after the internal use of drugs. 



Uses.— The drugs depressing the cortical motor area of 

 the brain are valuable in convulsions and spasmodic disorders 



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