OPIUM AND MOEPHIITE 363 



bral depression, while large doses give rise to spinal reflex 

 excitability in the lower animals — especially in the horse, 

 ass, cattle and cats. 



2. On the spinal cord. Small medicinal doses depress 

 the motor cells, bnt large and toxic amounts stimulate the 

 motor cells indirectly and cause convulsions — probably — as 

 in strychnine poisoning — by increasing the activity of the 

 receptive and transmitting cells of the cord. 



Convulsions, caused by spinal and cerebral motor stim- 

 ulation, rarely occur in man or dogs but are common after 

 toxic amounts in horses, cattle and cats. The result of a 

 fatal dose is paralysis of the central nervous system, includ- 

 ing the respiratory and, to much less degree, the vagus and 

 inhibitory centres. 



The unique and inestimable value of opium depends 

 tipon its anodyne action. Kelief from suffering is often in- 

 duced without the production of sleep. 



Muscular weakness is present in man and dogs, but even 

 this evidence of depression may be absent in horses and rumi- 

 nants, yet pain be effectually relieved. 



Initial stimulation of the vomiting centre may cause 

 emesis; but, as depression of the centre rapidly ensues, the 

 act becomes later improbable. The excitability of the motor 

 and sensory nerves is slightly increased, but otherwise the 

 nerves are not affected except in poisoning, when the sensory, 

 and later the motor nerves are paralyzed. The muscles 

 remain uninfluenced. 



Respiration. — Opium does not influence the respiratory 

 functions in small therapeutic doses, but large doses make 

 the respiratory movements slower and feebler, and^ death oc- 

 curs from the direct depressing and paralyzing action of the 

 drug upon the respiratory centres in the medulla. 



Circulation.— Small doses commonly produce little effect 

 upon the heart. Large doses first increase the force and 

 then slow the heart's action, while toxic quantities de- 

 press the organ. The cardiac muscle is primarily 



Digitized by Microsoft® 



