STAINING REAGENTS. 73 



The aniline colours are divided by Elirlich into ariil, L//xic, and 

 neutral compounds. Of the three, the basic colours are most used, 

 us 11 icy are excellent nuclear stains. Some of them have special 

 affinities for certain tissues, and, as is well known, they are of the 

 utmost value in bacteriological investigations. They may be kept 

 in drop bottles. All of them are soluble in alcohol, and most of 

 them in water ; and so powerful are they, that usually a i per cent., 

 or even a much weaker solution, suffices to stain tissues in a few 

 minutes. Some of them, according to Ehrlich's researches, stain 

 better when they arc mixed with a mordant. 



Aniline-Oil and Aniline- Water (Khrlich's Method). Shake up 

 excess of pure aniline-oil with excess of water, and allow it to stand. 

 The most of the oil sinks to the bottom. This solution should not 

 be kept too long ; in fact, it is better to make it fresh. Filter a 

 little of the aniline-water into a watch-glass. To the fluid in the 

 watch-glass add ten or twelve drops of a concentrated alcoholic 

 solution of any of the aniline dyes it is desired to use in this way. 



Very few of the preparations stained by aniline dyes can be pre- 

 served in glycerine or Farrant's solution. A 50 per cent, solution 

 of acetate of potash keeps their colours well, but it is a medium 

 which it is difficult to keep tightly under the cover-glass. Many of 

 them can be preserved in balsam, but most of them must be kept 

 away from the action of acids. In a few cases the colour is partly 

 extracted and fixed with dilute acids, but in such cases the free acid 

 must be removed from the section before it is finally mounted. 



For convenience these colours may be grouped as follows : 



(A.) Violet Aniline Colours. 



Methyl Violet. Dissolve 2 grams in TOO cc. and filter. This 

 gives a 2 per cent solution, which may be diluted as required. A 

 o. i per cent, solution is, in many cases, sufficient. It does best for 

 porous textures. Sections are left to stain in it for several hours, 

 washed with water, and then with alcohol, until no more colour 

 comes away, and mounted in balsam. It stains intercellular sub- 

 stances but slightly, while cells, and especially their nuclei, are 

 stained by it. 



Gentian Violet always answers very well for staining cell-nuclei, 

 but it seems to be better for hardened preparations than the 

 previous dye. 



Dahlia is used in the same way as the preceding. 



(B. ) Blue (and Purple) Aniline Colours. 



Aniline Blue. Make a i per cent, watery solution, adding a few 

 drops of absolute alcohol. This is useful for the glands of the 

 stomach and for a double stain with safranin. 



Methylene Blue. Make a saturated watery solution. Rectified 

 spirit may be added to make it keep. It is not very largely used 

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