REAGENTS AND PROCESSES 539 



aqueous stain immediately to xylol or to Canada balsam, for the reason that water 

 does not mix with these substances. Always, in going from water to oil or a 

 resinous solution, strong alcohol should intervene, and, of course, the same precau- 

 tion must be taken in going from the oil or resinous solution to water. 







Eau de Javelle. Prepared by adding to an aqueous solution of chloride of lime 

 a solution of potassium oxalate so long as a precipitate is formed. The solution is 

 then filtered and diluted somewhat with water before using. Or 20 parts of a 20 

 per cent, solution of calcium chloride is diluted with 100 parts of water, and after 

 this has stood for some time, a solution of 1 5 parts of pure potassium carbonate in 

 100 parts of water is added. If a film should form on the surface of this on exposure 

 to the air, a few drops of the solution of potassium carbonate should be added and 

 the precipitate filtered away. 



Lignin is extracted from sections of woody tissues which have lain in the eau de 

 Javelle solution for some time, and thereafter, on treating with chloroiodide of zinc, 

 the membranes show only a cellulose reaction, staining only purple with the 

 chloriodide of zinc. 



Starch-grains included in chloroplasts may be demonstrated by first treating 

 sections, or even whole leaves, with eau de Javelle until the chloroplasts are dis- 

 solved (this may take from one to twenty-four hours), and then treating the ma- 

 terial with a solution of potassium iodide-iodine. The starch-grains will take on 

 a blue or violet color. In some cases, however, the starch-grains themselves are 

 dissolved with the eau de Javelle. In such cases, and indeed in most cases, chloral 

 hydrate and iodine is to be preferred for demonstrating starch-inclusions in 

 chloroplasts (see under this head). 



When the forms of the cells simply are to be studied, eau de Javelle is very use- 

 ful in clearing the sections by dissolving the cell-contents. If the sections become 

 too clear in the eau de Javelle, this defect may be corrected by treating the sections 

 with alcohol or with a solution of alum. See under Cyanin for use of eau de Javelle 

 in differentiating cutinized and suberized membranes. 



Eosin. An aqueous solution of eosin is an excellent stain for protoplasmic cell- 

 contents and cellulose walls. The solution should be quite dilute. For the use of 

 eosin in double staining see under Cyanin and Gram's Method. See also in the 

 next chapter under Aleurone Grains. 



Erythrosin. This is really an eosin, but there is some difference in the method 

 of manufacturing. It is a more precise and a more transparent stain than eosin, 

 and is to be preferred for nearly all staining of paraffin sections. Make a i per 

 cent, solution in distilled water or in 70 per cent, alcohol. It gives good results 

 when made up according to the general formula. Erythrosin stains rapidly, 

 thirty seconds to two minutes being sufficient. When used in combination with 

 other stains, erythrosin should come last. 



Ether. Used with equal parts of 95 per cent, alcohol as a solvent of collodion; 

 solvent of ethereal and fatty oils. 



Fehling's Solution. Prepare three separate solutions: (i) 17.5 Gm. of copper 

 sulphate in 500 mils of water; (2) 86.5 Gm. of sodium-potassium tartrate in 500 

 mils water; (3) 60 Gm. of caustic soda in 500 mils of water. To prepare for use 

 mix i volume of each of these with 2 volumes of water. The solutions keep well 

 separately, but the mixture becomes changed after a time, and for this reason the 

 solutions should not be mixed until needed. 



Sections may be treated with this solution on the glass slip. Two small drops 

 of distilled water are placed on the slip with i drop of each of the three solutions; 



