Methods for Hardening and Fixing Tissues. 



Alcohol. 



When possible to cut the tissue into small pieces 

 about one quarter to one-half inch cube, it is best to place 

 them at once into 95% alcohol; here they remain 

 for four or five days, and are then transferred to absolute 

 alcohol for 24 to 48 hours. It is always well to place a 

 layer of absorbent cotton in the hardening jar to prevent 

 the tissues from resting on the bottom. The fluid can 

 then more readily touch all surfaces of the tissue to be 

 hardened. Gland tissue, such as salivary glands and 

 pancreas, also the intestinal canal, are well hardened by this 

 method. Kahlden states that this method is especially 

 useful when the tissues are to be examined for bacteria. 



Bichloride of Mercury Solution. 



Make a saturated aqueous solution of bichloride of 

 mercury. This is most easily done by dissolving 80 to 100 

 grins, of the salt in a liter of hot distilled water, and setting 

 this supersaturated solution aside to cool. The excess will 

 then precpitate out, and the cold saturated solution can 

 then be decanted. 



Only small or thin pieces, not thicker than -Jth of an 

 inch should be placed into this hardening fluid. They 

 remain in the solution for 12 to 24 hours, are then 

 thoroughly washed in flowing water for 12 to 24 hours, 

 transferred .to 70% alcohol for 24 hours, and 95% alcohol 

 for another day. This is one of the very best of harden- 

 ing fluids, and can be used to advantage for hardening all 

 glands, mucous membranes, muscle, etc. It is especially 

 useful for hardening pathological tissues. Almost any 

 staining fluid may be used after it. 



