118 METHODS OP MICROSCOPICAL RESEARCH. 



blocks may be preserved until required for section- 

 ising. The purpose, in embedding in celloidin, is 

 to secure the normal position (in situ) of all the 

 component parts of an organism or specimen. The 

 film of celloidin surrounding all the organs and 

 parts, and preserving their respective features and 

 positions, must be retained, and mounted with the 

 section. When these sections are to be mounted in 

 Canada balsam, they must be cleared in xylol and 

 phenol (as oil of cloves destroys the celloidin) and 

 mounted in xylol balsam. Celloidin sections may 

 be mounted in glycerine, glycerine jelly, or Farrant's 

 medium, all of which render the celloidin nearly as 

 transparent as does balsam. These sections may 

 be stained by means of all the ordinary staining 

 fluids, except, perhaps, one or two of the more 

 powerful anilin dyes which sometimes, though 

 curiously enough not invariably, colour the cel- 

 loidin indelibly. If stained by logwood they should 

 be strongly stained in order to admit of the extrac- 

 tion of the colour from the celloidin by the acetic 

 acid process, whilst the tissues remain sufficiently 

 stained. 



Specimens embedded in celloidin should be cut 

 by the ether freezing process. 



Gum and Syrup. For ordinary tissues 

 make a mixture of 5 parts of gum mucilage B.P. 

 and 3 parts of simple syrup B.P. For nerve, 

 brain, spinal cord, and any brittle tissues the com- 

 bination should be 5 parts of gum mucilage to 4 

 parts of syrup. 



Tissues and specimens to be cut upon the ether 

 freezing microtome are to be immersed in this fluid 

 for three or four days. They may be preserved for 



