108 CELLOIDIN 



Canada balsam. The following oil mixture is to be recommended 

 for routine work : — 



Creosote . . .40 c.c. 



Bergamot oil . . 30 c.c. 



Xylol .... 20 c.c. 

 Origanum oil . . 10 c.c. 



The sections are transferred from the oil to clean slides and the 

 major folds straightened out with mounted needles. It may be 

 necessary to use a dissecting microscope for thin sections. A 

 drop of Canada balsam is placed on the section and the coverslip 

 pressed down very firmly. In some cases a small lead weight must 

 be placed on top of the coverslip and allowed to remain overnight. 

 Dunham's mixture : — 



White oil of thyme . . 3 to 4 j^arts 



Clove oil . . . .1 part 



also serves the purpose of clearing and softening the celloidin. 

 The older clearing fluids containing carbolic acid should be avoided 

 owing to their deleterious action on anilin dyes. 



OTHER COLD MASSES 



197. Lead-Gum Imbedding Method of J. Salkind (C. R. Soc. 

 de Biol., Ixxix, 1916, p. 16). The principle of the method is 

 that an aqueous solution of gum treated by acetate of lead, when 

 exposed to the action of anmionia, is transformed into a gel, 

 sufficiently stiff to allow of thin sections being cut. 



1. Dissolve a quantity of gum of cherry (white for preference) 

 in double its weight of aq. dest. After filtration, add to the solution 

 one-third its volume of the liquid subacetate of lead (extract of 

 Saturne), to which has been added 5 per cent, of glacial acetic 

 acid. This gives a kind of thin collodion-like solution, in which 

 you place the pieces at room temperature, to be imbedded, after 

 a fixation, for which see below. 



2. Leave about twelve hours for pieces about a millimetre in 

 thickness : larger pieces must be left longer. After the correct 

 period has elapsed, you let the lead-gum solution evaporate in the 

 air till the solution reaches the consistency of a thick celloidin 

 solution. 



3. Arrange the pieces to be imbedded in a paper box (or on a 

 piece of paper), in a large drop of the thick solution. Expose to 

 strong ammonia vapour for about five minutes till the block 

 hardens to the consistency of cartilage. 



4. Trim the block, and fasten it on to the plate of a microtome 

 by means of some of the thick lead-gum (hardened afterwards 

 in ammonia vapour). Cut sections with an oblique knife, the 

 block being moistened with a solution 1 per cent, sodium chloride 



