SPECIAL METHODS. 321 



The solution should be cold before use. It cannot be filtered 

 through paper ; but if not clear, should be decanted from any sedi- 

 ment, or a fresh solution prepared. Maceration takes place very 

 quickly in this solution. The tissues can usually be teased apart 

 within fifteen to thirty minutes. They must be examined in the 

 potash solution without dilution, as the addition of water quickly 

 destroys the tissue-elements. For this reason the specimens to be 

 macerated should be placed in several times their bulk of the pot- 

 ash solution ; otherwise the water they contain will dilute the pot- 

 ash. Permanent mounts cannot be made. 



c. Chromic acid. A solution of 1 part of the acid in 10,000 

 parts of distilled water will facilitate the teasing apart of tissue- 

 elements which have macerated in it for one to several days. After 

 careful washing on the slide alum-carmine alone, or followed by 

 picric acid, may be used for staining. 



4. Methods of Decalcification. — Tissues which contain calcified 

 nodules or bone must be freed from lime-salts before they can be 

 cut. It is difficult to do this rapidly without injury to the softer 

 tissue-elements. When good results are desired, and the necessary 

 time can be afforded, the tissues should first be fixed and hardened, 

 small pieces being selected. Zenker's fluid fixes well for this pur- 

 pose, but Orth's fluid or alcohol may be used. If Zenker's or Orth's 

 fluid is used, the tissues must be washed in water and hardened in 

 alcohol for at least a day before they are decalcified. 



Decalcification is accomplished by treatment with acids. Five 

 per cent, nitric acid will decalcify small pieces of bone in from one 

 to five days. The progress of the decalcification may be deter- 

 mined by pricking the tissue with a needle, but after it appears 

 to be soft it is well to continue the action of the acid for a day or 

 two, lest some undissolved particles should remain and injure the 

 edge of the microtome-knife. A saturated aqueous solution of 

 picric acid is sometimes used for decalcifying. Its action is very 

 slow, though not injurious to the tissues, which require no prelimi- 

 nary treatment, the picric acid acting as a fixing and decalcifying 

 agent. 



After decalcifying in nitric acid the tissues should be thoroughly 

 washed in running water for twenty-four hours and then rehardened 

 in alcohol, after which they may be embedded. After decalcifying 

 in picric acid the tissues are placed in 70 per cent, alcohol and hard- 

 ened without previous washing in water. 



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