DyRING THE OPERATION OF PLUGGING. 33 



had been cut away, and the excess of saliva removed 

 with a napkin from the lingual surface of the teeth 

 and gums, a strip of the membrane was applied, 

 and after slight pressure with the finger, it adhered 

 firmly in its place. The free edge was allowed to 

 project about a quarter of an inch above the level 

 of the masticating surface of the teeth. A smaller 

 patch was placed over the orifice of the parotid 

 duct. After all moisture was removed from the 

 cavity, the introduction of the gold was com- 

 menced. The operation extended over twenty 

 minutes, during which time the tongue, loaded with 

 saliva, could be seen moving against the insoluble 

 surface of the membrane, but without a particle of 

 fluid gaining access to the tooth. The new material 

 was experimented with in numerous cases, and with 

 equally favourable results. 



An unexpected dijficulty, however, arose. When 

 the gelatine had become perfectly dry, it parted from 

 the gutta-percha membrane. Various means were 

 tried by Messrs. Bell to overcome this difficulty, but 

 hitherto without success. In the mean time I have 

 used a membrane made in the following manner. 

 Several coats, either of gelatine or gum-arabic, are 

 laid upon one side of a piece of thin muslin. When 

 perfectly dry, the opposite side of the fabric is painted 

 over with a solution of gutta-percha. The mem- 

 brane so made answers quite as well as that first 

 described, but it is not (what the chemist would 

 call) an equally elegant preparation. Thin silk or 



