SPECIAL STAINS. 413 



water, stained with haematoxyline and mounted in glycerine which clears 

 them. They are not dehydrated in alcohol since strong alcohol dissolves 

 the fat and its stain. 



Osmic acid in i per cent, aqueous solution stains fat in fresh tissues 

 dark brown or black; myelin responds like fat both to osmic acid and 

 Scharlach R. The fat is blackened in tissues preserved in a mixture of 2 

 parts of Miiller's fluid (p. 404) and i part of the i per cent, osmic acid solu- 

 tion. Tissues should remain in it for about a week, after which they are 

 transferred to dilute alcohol (50-70 per cent.) for a few days. They may 

 then be imbedded in paraffin in the usual way, since the stained fat is 

 rendered insoluble in alcohol; it dissolves in xylol however, so that the 

 sections should be cleared in chloroform and mounted in damar dissolved in 

 chloroform. 



Blood may be stained for the study of leucocyte granules and blood 

 plates with Wright's stain which should be prepared as follows: After 0.5 

 gr. of sodium bicarbonate has been completely dissolved in 100 cc. of dis- 

 tilled water, add i gr. of Griibler's methylene blue (either the form called 

 BX, Koch's, or Ehrlich's rectified). "The mixture is next to be steamed in 

 an ordinary steam sterilizer at 100 C. for one hour, counting the time after 

 steam is up. The heating should not be done in a pressure sterilizer, or 

 in a water bath, or in any other way than as stated." After the steaming 

 the mixture is taken from the sterilizer and allowed to cool, the flask being 

 placed in cold water if desired. When cold it is poured into a large dish or 

 flask. To looc.c. of the mixture add about 500 cc. of a y^ per cent, solution 

 of Griibler's yellowish cosine soluble in water. The amount of the cosine 

 solution should be determined by the appearance of the mixture which it 

 forms, the whole being stirred if in a dish, or shaken if in a flask, while the 

 cosine is added. The color changes from blue to purple, and a yellowish 

 metallic scum forms on the surface, "while on close inspection a finely 

 granular black precipitate appears in suspension." The solution is then 

 filtered and the precipitate is allowed to become perfectly dry upon the 

 filter paper. The stain is made by dissolving 0.5 gr. of the precipitate in 

 100 c.c. of pure methyl alcohol. The stain need not be filtered, and like the 

 precipitate it keeps indefinitely. If by evaporation of the alcohol it becomes 

 too concentrated, as is shown by the formation of precipitates when it is used, 

 it should be filtered and a small quantity of methyl alcohol added. 



Blood is obtained usually from a needle puncture in the lobule of the 

 ear. Two cover glasses, perfectly clean and dry, should be at hand. When 

 the blood is flowing freely, the center of one of the covers is touched to a 

 small drop as it emerges, and is then immediately inverted and dropped 

 upon the other cover. The blood should spread evenly between the two 



