MICROSCOPIC TECHNIQUE AND REAGENTS. 757 



contents. Among the clearing agents most frequently employed 

 are: Chloral in saturated aqueous solution, and chloral-glycerin 

 solution (a solution of equal parts of glycerin and water saturated 

 with chloral). Essential oils, as clove, turpentine, cedar, mar- 

 joram, etc., are also useful for this purpose, particularly when 

 the specimen is to be mounted in Canada balsam. 



Staining Agents are those that produce more or less defi- 

 nitely colored compounds with the cell-contents or -walls. They 

 include: (i) the Aniline Dyes and (2) Non-aniline Stains. 



The aniline stains may be used in aqueous solutions, weak 

 alcoholic solutions or strong alcoholic solutions, containing from 

 I to 3 per cent, of the dye. The following are the aniline stains 

 most frequently employed : Aniline blue, Bismarck brown, fuchsin, 

 gentian violet, methylene blue, methyl violet and safranin. In 

 addition to these, aniline hydrochloride or sulphate is used in what 

 is known as Wiesner's Reagent, which is a 25 per cent, solution of 

 alcohol containing 5 per cent, of either of these salts, a drop of 

 either hydrochloric or sulphuric acid being used with a drop of the 

 solution, according as the hydrochloride or sulphate has been used. 



Loffler's Methylene Blue. — This reagent is prepared by 

 adding 30 c.c. of a concentrated alcoholic solution of methylene 

 blue to 100 c.c. of water containing 10 milligrams of potassium 

 hydrate. 



Ziehl's Carbol-fuchsin. — This solution is prepared by add- 

 ing 15 c.c. of a concentrated alcoholic solution of fuchsin to 

 100 c.c. of water containing 5 grams of carbolic acid. 



Aniline Dyes are usually employed in concentrated aqueous 

 solution, but owing to the difference in solubility of the dyes the 

 solutions vary in strength. Saturated solutions of eosin or gen- 

 tian violet may be prepared by dissolving i gram of the dye in 

 100 c.c. of water, while to make a saturated solution of methylene 

 blue requires 0.400 Cm. of the dye to 100 c.c. of water. Some 

 investigators prefer to replace the distilled water with aniline 

 water, which is prepared by adding about 3 grams of anilin oil to 

 100 c.c. of distilled water. 



Reagent Bottle for Sterile Solutions. — The solutions of 

 the aniline dyes as ordinarily prepared deteriorate more or less 

 rapidly and are usually made up fresh each time they are required 



