CELLOIDIN 101 



infiltration. Generally speaking, four distinct stages are involved 

 after the fixation of the tissue. 



1. Complete dehydration, followed by soaking the tissue in 

 the celloidin solvent. 



2. Infiltration of the tissue with increasing concentrations of 

 celloidin, starting with a 2 per cent, solution. 



{a) Infiltration at room temperature, or 



{h) Infiltration under pressure at 50° to 60° C. (The hot 

 celloidin technique). 



3. Imbedding the tissue in concentrated celloidin (8 to 15 per 

 cent.) followed by carefully controlled evaporation of the solvent 

 so that the celloidin sets in a firm block, or 



Imbedding the tissue in celloidin which is concentrated by adding 

 fresh dry celloidin and heating under pressure until the imbedding 

 mass becomes viscous. 



4. Hardening of the block of precipitated celloidin to give it 

 adequate rigidity for cutting the sections. 



183. Preparation before Infiltration. Before proceeding with 

 final dehydration in absolute alcohol, it is important to remove 

 gases from such tissues as lung and from organs with cavities or 

 extensive lavers of loose connective tissue. The tissue in most 

 cases can be placed in 70 or 90 per cent, alcohol under an exhaust 

 pump but, where the rapid evolution of gas bubbles is likely to 

 damage the tissue, the alternative method of using alcohols from 

 which dissolved gases have been removed by heating is advised. 

 If the piece of tissue contains large masses of adipose tissue it is 

 better to extract the fat by transferring it to benzol and then 

 returning it to several baths of absolute alcohol before proceeding 

 with the celloidin infiltration. 



The dehydration of the tissue must be very thorough. A few 

 crystals of phenol added to the last two baths of absolute alcohol 

 or the more elaborate methods of re-distilling the alcohol, using 

 iodine and magnesium (Bjerrum and Lund, Brit. Chem. Abstr., 

 1931, 461 A), may be useful. Celloidin infiltrates tissues success- 

 fully after most routine fixatives, with the special exception of 

 Bouin's picro-formol-acetic mixture. Bolcek {Zeit. zviss. Mikr., 47, 

 1930, p. 334) recommends placing Bouin fixed material for ten 

 to forty-eight hours from 96 per cent, alcohol into : — 



Cedarwood oil . . 10 c.c. 



Absolute ethyl alcohol . 80 c.c. 



Origanum oil . . . 20 c.c. 



Nitric acid . . .10 c.c. 



The tissue is then washed for twenty-four to forty-eight hours in 

 96 per cent, alcohol and is ready for complete dehydration and 

 infiltration. 



After dehydration the tissue is placed in equal parts of absolute 

 ethyl alcohol and ethyl ether (0-72, water free), the celloidin 



