Fixation, Blochi)ig, and Sectioniyig 63 



Fixation, Blocking, and Sectioning 



Fresh tissues may be used, but it is preferable to fix the material, 

 usually in formalin, which leaves the tissue in a consistency ideal for the 

 freezing technic. FormalirLis a water solution and requires no washing. 

 Harfz {1945), however, recommends Bouin's as better than formalin, 

 but says that the tissue must be washed for a short time before freezing. 

 If the fixative contains mercuric chloride, the crystals may be removed 

 immediately after sectioning with an iodine solution, such as Lugol's, 

 which contains no alcohol. If the tissues are extremely friable it may 

 be advantageous to embed them in gelatine (page 66) or immerse them 

 in a thick aqueous gum syrup, such as gimi arable. 



When it is necessary to section immediately (example: surgical bi- 

 opsy), and yet fixation is desirable, boil a small piece for a couple of 

 minutes in 10% formalin. Rinse in water and freeze. Reiner (1953) 

 adds tissue to imdiluted formalin at room temperature, then heats the 

 solution and tissue to 56-60 °C in a water bath for 2 minutes. Agitate 

 the tissue during the heating^. Reiner claims inferior results without 

 agitation and also says that placing tissues in preheated formalin is dis- 

 advantageous. 



Friedland (1951) Method, Using Agar 



1. Boil tissue in formalin. 



2. Replace formalin with 2% sterile agar (previously heated to its melt- 

 ing point) in w'ater. Boil gently 1 minute. 



3. Pour off and freeze tissue immediately. 



The Agar can be kept ready in Pyrex tubes, and melted quickly over 

 an open flame. 



Lev and Thomas (1955) Method 



This method fixes tissue at 80°C and produces excellent residts. The 

 following solution is placed in a baby's bottle-warmer and comes to a 

 boil in I minute. Add the tissue and allow it to boil for 1 more minute. 



formalin 10.0 ml. 



glacial acetic acid 1.0 ml. 



95% ethyl alcohol 80.0 ml. 



The tissue will have to be washed to remove the alcohol before freez- 

 ing can be attempted, possibly a disadvantage w^hen speed is impera- 

 tive. 



