128 



Scientific Proceedings (75). 



therefore, would seem to be a central one, probably in the nature 

 of a depression of certain central structures concerned with the 

 vomiting act, or of certain paths to or from the central mechanism. 

 It should be stated that the dose of atropin required to antagonize 

 the minimal emetic dose of pilocarpin is insufficient to dilate the 

 pupil and does not appreciably diminish the salivation or diarrhea 

 produced by the pilocarpin. The mechanism of antagonism 

 between atropin and nicotin is apparently the same as between 

 atropin and pilocarpin, and it is interesting to recall the fact that 

 nicotin and pilocarpin — the only central emetics which we have 

 found so far to be antagonized by atropin — are very closely related 

 in their pharmacologic actions. 



Atropin is stated to be capable of preventing the emesis often 

 seen following the therapeutic use of morphin in man and that 

 induced in dogs. The mechanism of this action is usually given 

 as involving a local action of both drugs on the stomach, morphin 

 emesis being ascribed largely to a marked stimulation of the motor 

 endings of the vagus in the stomach, which are depressed by 

 atropin. In dogs, at least, morphin has been shown 1 to produce 

 emesis through a central action and we have not been able to 

 prevent this action by atropin in any dose. This failure con- 

 firms the observations of Guinard, 2 who, however, conceded some 

 antagonistic action between atropin and morphin in man, which 

 he thought due to a synergistic central depressant action of the 

 two drugs. 



The failure of atropin to antagonize the central emetics studied, 

 other than pilocarpin and nicotin, raises several interesting points 

 regarding the physiology of vomiting. We are all aware of the 

 number and diversity of ways by which vomiting may be induced 

 and of the existence, therefore, of many afferent paths for the 

 stimulation of the central vomiting mechanism. It is suggested, 

 on the basis of the present observations, that atropin antagonizes 

 nicotin and pilocarpin on the one hand by depressing some limited 

 portion of the vomiting center, and on the other hand fails to 

 antagonize the other centrally acting emetics used since these 

 may possibly influence the central mechanism through other and 

 different portions. 



1 Loo. ext. 



''■Lyon Medical, 1895, LXXX, pp. 37 and 49. 



