ADDITIONS. 391 



for one day to a week or more. (6) Whilst the 

 tissue is in absolute alcohol ^ voL ether is added, 

 and then celloidin in small fragments from day to 

 day, so that solution slowly goes on and a fairly 

 thick solution is obtained in 8 to 10 days. 



Celloidin hardened in, 80 p.c. alcohol. The tissue is 

 removed from the celloidin solution, placed on a 

 cork and a little of the solution poured over it; 

 when a thin film has formed on the surface of the 

 celloidin the whole is put in alcohol 80 p. c. In a 

 day or more the tissue can be cut. During cutting, 

 the razor should be kept wet with 70 to 80 p. c. 

 alcohol. Instead of fixing the tissue to cork it may 

 be placed in a small paper case, celloidin poured 

 over it and treated as above. When the outer part 

 is firm the paper should be removed. 



Celloidin hardened in chloroform. Chloroform is used 

 instead of the 80 p.c. alcohol of the previous section ; 

 or a little celloidin solution is gently poured on chlo- 

 roform, when the lower surface is firm the tissue 

 is placed on the celloidin and more of the solution 

 poured over it. The celloidin shrinks much less 

 and remains more transparent with chloroform than 

 with alcohol. 



Celloidin hardened by evaporation. The tissue is re- 

 moved from celloidin solution to a small watch glass 

 with a thin layer of celloidin over it, the small watch 

 glass covered with a larger one for two or three hours 

 till the celloidin is fairly firm, it is then coated with 

 fresh celloidin, allowed to dry partially, and so on 

 until (in 1 to 3 days) a sufficient coating of firm 

 celloidin is obtained. Or the tissue with celloidin 

 may be poured into a small glass dish, this covered 



