—159— 



the stain 10 to 15 minutes, are then waslied in acid alcohol 

 or in 70% alcohol to which a few crystals of picric acid 

 have been added; remove acid by transferring sections to 

 70% alcohol. Dehydrate, clear in oil of bergainot, and 

 mount in balsam. 



Orth's Picro-Lithium Carmine Solution. 



To three parts of the al)ove lithium carmine solution 

 add one part of a saturated aqueous soIuiIdm oI" picric acid. 

 Sections stain in 10 to 20 minutes. Wash in 70% alcohol 

 to which a few crystals of pit-ric acid have been addiMl. 



ANILINE DYES. 



It would lead far beyond the scope of this guide, to 

 mention even very briefly, the various aniline dyes that 

 have found their way into microscopical technic. The 

 certainty and ease with which many of the microorganisms 

 are stained by them, has made them very useful in hacter- 

 iological work. Their use, as staining agents for tissues, 

 dates back to 1863, at which time Waldeyer and Frey made 

 use of one of the fuchsins for staining tissues. Since that 

 time an ever increasing number of these dyes has been 

 tried, and recommended by various investigators. The few 

 here mentioned have proved themselves most useful in the 

 hands of the author. 



Ehrlich classifies all aniline dyes, as basic, 

 neutral, or acid. In a general way we may say that the 

 basic dj'cs, such as methylene blue, methyl green, gentian 

 violet, methyl violet, Bismark brown, sdfranin, etc. are to be 

 used when it is desired to stain the nucleus, while the acid 

 aniline dyes, such as eosin, orange G, acid fuchsin, lichtgrun, 

 aurantia, and nigrosin are generally used for staining the 

 protoplasm of cells. 



Almost all aniline stains are readily soluble in alcohol 

 or water, and, as they stain very deeply and quickly, only 

 dilute solutions (0.5 to 1%) are recommended. The 

 majority of the basic stains give the best results when 

 combined wdth aniline water, but as nearly all stain 

 diffusely, the sections need to be thoroughly washed in 

 water, alcohol, or acidulated alcohol before mounting. 



