SECTION THREE 



4, Fix the Celloidin block to the wooden or vulcanite block as 

 described in step 10 (above). 



5. Sections may now be cut without the necessity of moistening 

 the knife or the block. 



Note: Blocks prepared by this method are stored in a dry wide- 

 mouth stoppered bottle. 



CELLOIDIN - PARAFFIN WAX (Double Embedding) 

 For serial sections embedded in Celloidin 



Solution required: 

 Celloidin 1% in Methyl Benzoate 



This is prepared by adding the appropriate weight of air-dried 

 Celloidin flakes to a quantity of methyl benzoate in a clean dry 

 corked flask or bottle. Shake well; allow the flask or bottle to 

 stand upright for an hour or so ; then leave it inverted for an hour, 

 afterwards leave it lying horizontally for a time; then stand it 

 upright again, and repeat the process at intervals throughout the 

 day and leave the bottle lying on its side overnight: next morning, 

 solution should be complete and it is only necessary to shake the 

 bottle well to ensure a homogeneous solution. 



Technique: 



1. Tissues are fixed and washed in running water, and any mer- 

 curial precipitate removed in the usual manner. 



2. Immerse for two hours in each of the following: 50%, 70% 

 and 90% alcohol. 



3. Transfer to absolute alcohol for two to sixteen hours. 



4. Immerse in Methyl Benzoate - Celloidin solution for twenty- 

 four hours, at the end of w^hich time pour off the solution and 

 replace with a fresh lot in which the tissue should remain for a 

 further forty-eight hours : if the tissue is not now clear, transfer it 

 to a fresh lot of Methyl Benzoate - Celloidin solution for a further 

 period of seventy-two hours. 



5. Immerse in three changes of pure benzene, for four hours in 

 the first lot, eight hours in the second, and twelve in the third, 



489 



