ON STAINING FLUIDS, AND STAINING. 117 



Embedding in Celloidin. 1 This delicate and 

 cleanly and most effective process is pursued as 

 follows : 



A thin solution of the celloidin is made in equal 

 parts of absolute alcohol and ether. 



A thick solution is also made in the same manner, 

 by increasing the proportion of the celloidin. 



The specimens perfectly dehydrated are to be 

 placed in absolute alcohol for twenty-four hours, and 

 then transferred into a mixture of equal parts of 

 absolute alcohol and ether for a second period of 

 twenty-four hours. 



They are now to be immersed in the thin solu- 

 tion of celloidin for twenty-four hours, and after- 

 wards in the thicker solution for three days. 



They are then to be placed in paper trays, so 

 made as to admit of a good margin of celloidin sur- 

 rounding the specimen occupying the centre of the 

 tray. The tray is then to be filled with the thick 

 solution of celloidin, which is to be allowed to 

 evaporate, the tray being filled up from time to 

 time, as evaporation goes on, until the specimen 

 is covered, as well as surrounded, by a layer of 

 celloidin in other words, embedded in a block of 

 celloidin, of the size and shape of the tray. When 

 the celloidin begins to set firmly, and before any 

 shrinkage sets in, the tray, with the specimen, is 

 to be plunged into a vessel with an air-tight cover, 

 containing strong methylated spirit, and in this the 



1 " Schering's Celloidin," which is patented, can be obtained 

 at Mr. C. Baker's, 244, High Holborn, London, W.C. The 

 celloidin shavings, recently introduced, will be found much 

 more convenient to use than the tablets. 



