Fixing the Tissue 11 



8. Maceration by enzymes, good for connective tissue, reticulum. (Gali- 



gher, 1934) 

 Place frozen sections in: 



pancreatin siccum 5.0 gm. 



sodium bicarbonate 10.0 gm. 



distilled water lOO.O ml. 



wash thoroughly and stain. 



Fixing the Tissue 



First consideration in the choice of fixative should lie in the purpose 

 to be served in preparing the tissue for future use. Is a routine all-pur- 

 pose fixative adequate or nnist some special part of a cell be preser\'ed? 

 For example: an aqueous fixing fluid will dissolve out glycogen, and an 

 alcoholic one can remove lipids. Thought should be given to the rate 

 of penetration of the fluid and the density of the tissue to be fixed. Ob- 

 viously an extremely dense tissue might not fix well in a fixative which 

 penetrates slowly and poorly. With fixatives of poor penetration, the 

 size of the pieces must be trimmed to a minimum. In all cases, pieces 

 never should be any larger than is absolutely necessary; the smaller the 

 bulk, the more perfect the fixation. 



The hardening effect of fixatives should be considered. An excessively 

 hardening fixative might lead to difficulties with liver and muscle. Maybe 

 some other fixative could be used with less hardening effect. If there is 

 any doubt concerning future needs for a tissue, place it in formalin; 

 this can be foUoAved by post-fixation treatments. 



Use a large volume of fixing fluid — at least ten times the bulk of the 

 tissue if possible. Remove the tissues from the animal and place them 

 in the fixative as rapidly as is feasible, thereby reducing post-mortem 

 changes to a minimum. In most cases, do not attempt to fix the entire 

 organ; it will be too large to allow rapid and complete penetration of 

 the fixative. This is particularly true of an organ covered by a tough 

 membrane. An ideal piece would be 1 to 2 cm. in size; or place a larger 

 piece in the fixative for 15 to 30 minutes, then trim it to smaller size 

 and return it to the fixative. This sometimes is necessary when tissue 

 is very soft or easily crushed. Trim the piece with a new razor blade or 

 sharp scalpel. This will cause less damage than the squeezing action of 

 scissors. Do not crush or tear the tissue while removino ii; such material 

 is worthless. Never allow tissue to become dry before placing it in the 



