102 OELLOIDIN 



solvent. Very small pieces of tissue will require only one hour's 

 soaking or they may be transferred direct from absolute alcohol 

 to the celloidin solution. 



184. Infiltration. Celloidin may be obtained in solutions of 

 various concentrations (Gurr) or in the form of shreds stored in 

 water (Schering). The pure celloidin shreds must be washed in 

 absolute alcohol and dried at room temperature on thick filter 

 paper. It is convenient to make up two solutions, 8 and 16 per 

 cent., from which the intermediate concentrations can be quickly 

 made by dilution with the solvent. The dry celloidin is weighed 

 and placed overnight in a volume of absolute alcohol equal to half 

 the final volume of solvent. The celloidin swells, and when the 

 remaining volume of ether is added the celloidin dissolves after 

 a further twenty-four hours. Celloidin solutions should be stored 

 in double stoj^pered, wide mouthed bottles to prevent the escape 

 of ether (B.P. 34° C.) and to facilitate the pouring of thick solutions. 

 Storage in a refrigerator will minimise the evaporation of the 

 solvent in hot weather. 



185. Infiltration at Room Temperature. The piece of tissue is 

 placed successively in 2, 4, 6 and 8 per cent, celloidin for periods 

 extending from several days to one month in each solution. It is 

 impossible to state the time required for infiltration in any but 

 these vague periods as so much depends on the volume of the 

 material and the density of the various tissues involved. The 

 6 per cent, solution may be omitted for small pieces of tissue and, 

 generally speaking, the time can be cut down with more advantage 

 in the 8 per cent, than in the 2 and 4 per cent, solutions. Heavily 

 mordanted material requires prolonged infiltration {e.g. nervous 

 tissue, Weigert-Pal technique). 



186. Infiltration at 50°-60° C. Hot celloidin solutions are not 

 apparently injurious to delicate cytoplasmic structures and do not 

 cause increased shrinkage or hardening. 



The tissue is placed in 2 per cent, celloidin in a stout glass 

 bottle fitted with a heavy cork which is wired securely to the 

 neck of the bottle, see Walls {Stain Tech., vii, 1932, p. 135.). The 

 bottle is incubated for twelve to twenty-four hours at 50° to 60° C. 

 and the pressure of the ether and alcohol vapour forces the 

 celloidin into the tissue. A minimum of celloidin solution should 

 be used to give sufficient space in the bottle in which to develop 

 maximum pressure. The bottle can be inverted to prevent the 

 escape of ether through the cork. When the bottle is removed 

 from the incubator it is allowed to cool to room temperature 

 before removing the cork. The 2 per cent, celloidin is then 

 replaced with 4 per cent, and the cork rewired on to the bottle. 

 After a further twelve to twenty-four hours incubation, the 

 process is repeated for the 6 and 8 per cent, solutions. The method 

 is quite a safe one if reasonable care is taken, but it is essential 



