SPECI.\L STAINING METHODS 31 



4. Clear in carbol-xylol and xylol and mount in xylol-damar. 



(9) Maresh's Modification of Bielschowsky's Stain for 

 THE Finer Connective Tissue Fibrils. 



1. Very thin paraffin sections are fixed to the slide and placed for 

 twelve to twenty-four hours in a 2-per-cent. silver nitrate solution. 



2. For fifteen to thirty minutes in freshly prepared alkaline silver 

 solution (20 c.c. of 2-per-cent. silver nitrate solution, to which have 

 been added 3 drops of 40-per-cent. caustic soda, and the precipitate 

 redissolved by adding ammonia drop by drop while stirring). 



3. Rinsed quickly in distilled water and placed in 20-pcr-ccnt. 

 formalin for three minutes or until black. 



4. Washed in distilled water and transferred for ten minutes to 

 acid gold bath (10 c.c. distilled water to which have been added 2 

 or 3 drops of i-per-cent. gold chlorid and 2 or 3 drops acid). 



5. Placed one-half to one minute in 5-per-cent. jtiyposulphitc of 

 soda to remove all unreduced silver. 



6. Washed in distilled water, dehydrated, cleared in xylol and 

 mounted in balsam. 



(10) Osmic-acid Stain for Fat. — For this purpose osmic acid 

 is used in a i-per-cent. aqueous solution. The method is especially 

 useful for demonstrating developing fat, fatty secretions (mammary 

 gland), and fat absorption (small intestine). Very small bits of the 

 tissue are placed in the osmic-acid solution for from twelve to twenty- 

 four hours. They are then hardened in graded alcohols, embedded 

 in celloidin, and the sections mounted in glycerin. 



(11) Sudan III and Scharlack R for Fat.- — Either of these 

 dyes may be used in concentrated solution in 70-per-cent. alcohol. 

 Frozen sections of fresh or formalin-fixed tissue are used. They are 

 first placed in 50-per-cent. alcohol for several minutes, then trans- 

 ferred to this staining fluid for from fifteen to thirty minutes, washed 

 in water or in 50-per-cent. alcohol and mounted in glycerin or in 

 glycerin jelly. Both dyes stain fat intensely red. A nuclear stain 

 such as hsemalum, or a plasma stain such as picric acid, or both may 

 be used in conjunction with either Sudan III or Scharlack R. Sec- 

 tions are first stained in hsemalum, washed in water, transferred to 

 50-per-cent. alcohol, then stained with either the Sudan III or 

 Scharlack R, washed in water, transferred to an aqueous solution of 

 picric acid, w^ashed again in water and mounted in glycerin or 

 glycerin jelly. 



