85 



225. Sudan III. Fix tissue in formalin or Miiller's fluid. 

 Cut free-hand sections, employ the freezing microtome method, or 

 isolation ( 35 ). Rinse sections in 82% alcohol and transfer 

 sections to a strong solution of the stain in 82% alcohol; 

 leave several minutes covered from evaporation; rinse with 82% 

 alcohol and transfer to water. Mount in glycerin or glycerin jelly 

 ( 151, 155). Fat is stained red. 



226. Herxheimer's Stain. Preparation for staining is as above 

 ( 225). Pass sections into 67% alcohol. Transfer to a strong solu- 

 tion of Scarlet Red in 67% alcohol rendered alkaline by 2% of sodium 

 hydroxid. Stain for several minutes; rinse with 67% alcohol and 

 transfer to water. Mount in glycerin or glycerin-jelly. Fat globules 

 stained red. It affords a more intense stain than Sudan III. 



Indophenol (saturated solution in 67 or 82% alcohol) may be 

 used as a blue stain for fat in a similar manner. 



227. Osmic Acid. ( 30, 18, 19). Osmic acid is reduced 

 by the unsaturated fatty acids (e. g., oleic acid) which are blackened 

 by it. The saturated fats and fatty acids (e. g., stearic, palmitic,) 

 are not so blackened [1] but the black color subsequently appears 

 when the tissue is placed in alcohol [41]. The fat so oxidized and 

 impregnated with osmium (?) becomes less soluble in fat solvents 

 ( 224) and may be retained in tissue imbedded in either paraffin or 

 celloidin. There is, however, a difference in fats; adipose tissue is 

 easily preserved, while some of the fat granules found in the organs 

 require the special precautions mentioned below. 



Fix sections of tissue 2 to 3 mm. thick in Flemming's or Benda's 

 fluid for 2 days; dehydrate in 95% alcohol, and transfer to thin 

 celloidin, and subsequently thick celloidin made up with 95% 

 alcohol (not absolute). The sections may be stained in safranin, 

 quickly dehydrated and cleared with carbol-xylene and mounted in 

 balsam, either without a cover-glass, or in thick balsam melted by heat 

 and applied warm. Unless such precautions are taken, the solvent of 

 the balsam may in time dissolve out the granules of blackened fat. 



Paraffin does not afford as good a preservation of the more labile 

 fat globules. Dehydrate in equal parts of 95% and absolute alcohol, 

 clear before the infiltration in carbol-xylene or chloroform. Paraffin 

 in the sections should be dissolved out by carbol-xylene in preference 

 to xylene ( 143). 



