INCOMPATIBILirY . 83 



avoid incompatibility by (above all) simplicity in prescrip- 

 tion writing, i.e., the use of few drugs in combination. Water 

 or alcohol are generally the best solvents. 



II. Physical incompatibility consists in the production 

 of unsightly-looking mixtures, but without necessarily any 

 chemical alteration of their ingredients ; for example, the 

 addition of water to insoluble powders, oils and chloroform. 

 While such combinations are pharmaceutically improper, 

 they may sometimes be used to advantage in practice. 



III. Physiological incompatibility consists in the union 

 of drugs possessing antagonistic physiological actions.' For 

 instance, the combination of purgatives and astringents ; of 

 morphine and atropine ; of digitalis and nitroglycerin. Such 

 prescriptions may be valuable therapeutically when the 

 antagonism is not complete. This follows because, while the 

 deleterious action of one drug may be offset by another, its 

 beneficial effect may at the same time exist or be accentuated. 

 Thus the anodyne influence of morphine is increased by 

 combination with atropine, but both the depressing action 

 of morphine on the respiration and its constipating tenden- 

 cies are lessened by atropine. 



