36 GENERAL ACTION OF DRUGS 



ness, sensation and motion. Between these two stages — the stimulant 

 and the anesthetic — there sometimes occurs a transient state in which 

 sensation is lost before consciousness. This has been styled the anodyne 

 stage. 



Finally, the (3) paralytic statge 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 involuntary micturition and defecation occurs. The ani- 

 mal 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 of that in which they were lost; i.e., the lower vital 

 functions first appear, followed finally by the higher cerebral functions. 



Uses. — Anesthetics are employed in surgical operations to relax 

 muscles and prevent pain and struggling; in obstetrical operations and 

 in the reduction of fractures, dislocations and hernia, to obtain 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 Anesthesia (p. 225). 



(c) Drugs acting on the cortical motor centres of the brain, 



(1) DRUGS STIMULATING THE MOTOR CENTRES. 



Strychnine Physostigmine 



Atropine 



(2) DRUGS DEPRESSING THE MOTOR CENTRES. 



The Bromides Alcohol 



Chloral Anesthetics 



The action of drugs on the cerebral cortical centres has been found 

 by comparing the local effect of electrical stimulation 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 and in motor excite- 

 ment, particularly in epileptiform convulsions of dogs. 



n. — Drugs Acting on the Spinal Cord. 



The functions of the cord consist in the conduction of sensory im- 

 pulses forward to tlie brain and of motor impulses backward to the 

 muscles ; in the origination of nervous force in centres controlling certain 

 functions (sexual, sweating, etc.) ; and in reflex action by which the cord 

 transmits impulses from sensory to motor tract of the same side of the 

 body, or laterally, from sensory to motor columns on opposite sides. 



While drugs probably influence the various centres in the cord, our 

 knowledge of their action is chiefly limited to that exerted on the motor 

 cells of the inferior cornua. 



If a drug stimulating the motor cells of the cord is given experi- 

 mentally, slight peripheral irritation will reflexly cause convulsions, and, 

 if the cord is severed from the brain, the same phenomena appear. 



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