392 ADDITIONS. 



with a flat piece of glass, allowing of a slow evapora- 

 tion of the alcohol and ether, so that the celloidin 

 becomes fairly hard in two or three days. 



Preparation for freezing. The celloidin around the 

 specimen, imbedded in one of the above ways, is 

 pared away and the block placed in water for an 

 hour or two, then transferred to gum for one or two 

 days or for any longer time. The block can then be 

 frozen and cut. Thinner sections can thus be ob- 

 tained than from celloidin alone. 



Staining sections. The sections still permeated by 

 celloidin may be stained with carmine or with hsema- 

 toxylin. Most aniline dyes stain the celloidin also. 

 If required, the celloidin may be dissolved out by 

 absolute alcohol, or by a mixture of absolute alcohol 

 and ether. 



Mounting. The celloidin need not be dissolved before 

 mounting. If sections are to be mounted in Canada 

 balsam and other substances which render it neces- 

 sary to dehydrate the tissue, this should be done 

 with 90 to 95 p.c. alcohol and origanum or bergamot 

 oil, instead of with absolute alcohol and clove oil, 

 since the latter dissolve the celloidin. Clove oil does 

 not however dissolve the celloidin very rapidly, so 

 that, if the sections are large, clove oil may be used ; 

 in this case the sections should be removed and 

 mounted as soon as they are clear. 



Mounting in glycerine-jelly. 



The glycerine-jelly may be made as follows : 

 Glycerine 70 c.c. 

 Water 60 c.c. 

 Gelatine 10 grams. 

 A little thymol or camphor, or carbolic acid. 



