APPENDIX 303 



III. IMBEDDING AND CUTTING TISSUES 

 IN CELLOIDIN. 



Tissues are imbedded in celloidin chiefly to avoid the 

 shrinking which in some cases occurs when they are heated in 

 melted paraffin. The disadvantages of the method as compared 

 with paraffin imbedding are that it takes longer, does not 

 allow such thin sections to be cut, and is less adapted for serial 

 sections. 



Celloidin solutions. Two solutions are used. T2 grams of 

 thin dry shavings of celloidin are dissolved in 10 c.c. of ether 

 and 10 c.c. of absolute alcohol. This gives the thin solution ; 

 the thick one contains about twice as much celloidin. 



5 c.c. of cedar- wood oil are sometimes added to the celloidin 

 solution. 



Dehydration. The tissue is in all cases dehydrated. This 

 is usually done with absolute alcohol ; the tissue being left in 

 it for several hours to a day or more according to the size of the 

 object. 



Large objects may be left in absolute alcohol and ether for 

 a day to increase the rate of penetration of the celloidin. 



Imbedding in celloidin. The dehydrated tissue is transferred 

 to celloidin, being left for two or more days in the thin solution 

 and for two or more days in the thick solution. 



If the piece of tissue is small the hardening of the celloidin 

 may be conveniently carried out as follows. A little thick 

 celloidin is dropped on a piece of cork, and exposed to the air 

 for about 5 minutes ; on this the object with some thick celloidin 

 is placed, and when a film has formed on the surface the whole 

 is placed either 



a. in chloroform (free from water) for an hour to a day ; 

 or b. in a desiccator and exposed to the vapour of chloroform 



for an hour to a day ; 

 or c. in 85 p.c. alcohol for a day or more. 



