646 Journal of Applied Microscopy. 



described by Erlich as formed by a mixture of acetic acid rosaniline and 

 ammonium-picrate. To quote from Erlich : " If concentrated aqueous solutions of 

 an acid and alkaline anilin dye be mixed so that the resulting mixture is neutral, 

 or nearly so, a precipitate appears which, when the proportions are right, is 

 abundant, but is soluble in excess of either the acid or alkaline dye." By mixing 

 a solution of eosin or erythrosin and methylin-blue, of methyl-orange and 

 methyl-green, of rubin and malachite-green, of picric acid and methylin-blue or 

 magenta-red, such precipitates are formed which are almost insoluble in water, 

 but can be dissolved in alcohol either directly or from alcoholic solutions obtained 

 by concentration of the solution or by the addition of water of crystallization. 

 The author especially values the mixture of eosin acid and methylin-blue for 

 biochemical purposes. The color of the liquid is changed from blue-violet or 

 green fluorescent to pure blue or blue-green, a return to the old color being pos- 

 sible by the use of organic acid, but not by mineral acids. Excess of alkalinity 

 changes the color to red, but neutralizing restores it. All acid substances are 

 colored blue, all alkaline red, all neutral violet. Hence celloidin, mucin or 

 nuclein stain blue, albumin, fibrin red. In tissue sections the nuclei are blue, 

 the protoplasm red, except with nerve cells in which the ground substance of the 

 protoplasm is rose-red, but Nissel's granules blue and the nuclei not blue. Since the 

 substances thus formed by mixtures are largely insoluble in water, only alcoholic 

 solutions are available, which serves well in leucaemia and malaria. A com- 

 prehensive application of these stains is possible, the " eosin-acid " methylin-blue 

 dissolves in a solution of methylin-blue or eosin better than in water, and the 

 more according to a greater concentration of the liquids. These solutions are 

 not then neutral, but basic with methylin-blue and acid with eosin, but they con- 

 tain the compounds necessary in saturate solutions. These solutions are par- 

 ticularly good in either diluted or aqueous solutions for tissue staining or the 

 demonstration of nuclear chromatin. By the combination further of neutral 

 stains another new series of anilin dyes is obtained, which have a 

 theoretical as well as practical significance. a. m. c. 



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13 figs. 



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