364 VEGETABLE DRUGS 



stimulated, with acceleration of the pulse, but depression 

 soon follows more or less synchronously with stimulation of 

 the vagus centre and endings, so that the pulse becomes 

 infrequent. Finally, before death, depression of the inhibi- 

 tory apparatus occurs, and this, coexisting with depression 

 of the heart itself, produces a feeble, rapid pulse, character- 

 istic of the last stage of opium poisoning. Death occurs 

 with diastolic arrest of the heart owing to failure of the 

 cardiac muscle, although fatality is mainly due to the 

 more powerful effect of the drug upon the respiratory 

 centre. 



The action of opium upon the vasomotor system is 

 unimportant. Immediately after the administration of large 

 doses there is a slight primary stimulation, followed in the 

 toxic stage by some depression of the vasomotor centres 

 in the spinal cord and medulla. 



Pupil. — The pupil of the horse is widely dilated by 

 large doses of opium. The pupil in the dog occasionally 

 remains unchanged, and often dilated before undergoing 

 contraction. Contraction of the pupil is a charactistic 

 physiological effect of large doses of opium, in man and the 

 dog. In birds the pupil is unaffected. These various con- 

 tradictory phenomena are at present inexplicable. 



In man, contraction of the pupil is brought about by 

 stimulation of the pupillary centre in the floor of the 

 aqueduct of Sylvius, and through it, the oculomotor nerves. 

 Dilatation, preceding death, occurs from depression of the 

 centre. 



Kidneys and Metabolism. — The excretion of urea appears 

 to be diminished by opium in man, but varies greatly in 

 animals. Temporary retention of urine may follow the 

 administration of a considerable dose of opium, owing to 

 diminished sensibility of the bladder. The amount of urine 

 voided may be greater or less than normal; more commonly 

 the latter. Opium lessens the secretion of bile. 



The elimination of carbonic dioxide is diminished by 

 the hypnotic action of opium, but is increased if there is 



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