38 ' Paraffin Method (chap. ?,) 



Quick hardening of outer surfaces will trap the air. When these prob- 

 lems arise, cool the blocks from the bottom, and with a hot instrument 

 keep the upper surface melted for a short time, thus releasing some of 

 the air. Then blow across the top until a scum forms, and ease the block 

 into water. This treatment also prevents excessive shrinkage in the 

 center of the block and the enclosed tissue. (Dempster, 1944.) 



If the paraffin does crystallize, difficulty may be encountered during 

 sectioning; the only remedy is to return the block to melted paraffin, 

 allow it remelt and repeat the embedding process. Experienced tech- 

 nicians soon learn how fast to handle the paraffin and reduce crystalliza- 

 tion to a minimum. 



Thoroughly hardened paraffin blocks can be stored indefinitely with- 

 out injury to the tissue, but they must be kept in a cool place where they 

 cannot soften or melt. 



Embedding Cellular Contents of Body Fluids 



"Cell blocks" are clusters of individual cells which have been concen- 

 trated and embedded for sectioning. The process for embedding them 

 is as follows: 



1. Collect the material in centrifuge tubes and add fixative: I hour, or over- 

 night. Agitate occasionally. 



2. Concentrate by centrifuging (preferably in small tubes); decant and add 

 water or alcohol depending on requirement of fixative. Loosen material 

 at bottom of tube and stir with small glass rod: 5-10 minutes, or longer. 



3. Centrifuge and decant. Add next solution and stir thoroughly. Dehydrate 

 in this manner, and clear: approximately 10-15 minutes for each step 

 depending on size of particles. 



4. Add melted paraffin and place tube upright in a glass or beaker in oven. 

 Stir slightly with warm instrument to work paraffin to bottom of tube: 30 

 minutes. Stir a bit once during this period. 



5. Cool test tube. 



6. Break tube. Place paraffin block in tiny paper box in a small dish of 

 paraffin in the oven. Leave only long enough for block to begin to soften. 

 Quickly cool paper box. 



Clark (1947) suggest an alternate method: 



1. Warm tube carefully in water, slightly warmer than paraffin. As soon as 

 paraffin against glass melts, tip tube and allow paraffin block to slide out. 



