l] MICROSCOPIC EXAMINATION 13 



these are preferable to those soluble in alcohol only. They 

 have all great affinity for cell nuclei (Hermann) and belong 

 to the group of neutral or basic aniline colours. Methyl- 

 blue, methyl-violet, vesuvin, Bismarck-brown, magenta, 

 fuchsin, gentian-violet, Spiller's purple, rosaniline, Hum- 

 boldt's red (purple), are the dyes most commendable. 



For staining of cover-glass specimens, as well as for sections 

 made of fresh tissues, the above dyes can be advantageously 

 used in the following manner : 2 to s grammes of the solid 

 dye are rubbed up in a mortar with 10 ccm. of absolute 

 alcohol ; add then gradually, while mixing, warm distilled 

 water, to bring up the total to 100 ccm.; filter and keep in 

 stoppered bottle. For use, filter a little of the dye into a 

 watch-glass. For staining film preparations or sections of 

 hardened tissues, the above dyes prepared with aniline 

 oil are preferable ; they are prepared thus : (a) Make a 

 saturated watery solution of pure aniline (aniline oil) by 

 mixing in a bottle one part of aniline oil with three parts 

 of distilled water ; shake well every half hour for four to 

 six hours, decant the water as the oil settles to the bottom. 

 The decanted fluid is the saturated watery solution of aniline. 

 Of this take 100 ccm. Add to this (3) a saturated alcoholic 

 solution of either fuchsin, gentian-violet, Humboldt's red, 

 methyl-blue or methyl-violet, 1 1 ccm. ; mix well, filter 

 into stoppered bottle. The sections are left in this dye for 

 from a few minutes to several hours (Humboldt's red 

 requires only a few seconds). Different bacteria require 

 different periods to stain. As a rule warming the dye 

 facilitates the staining of the bacteria ; occasionally, also, 

 the addition of a few drops of liquor potasss. All sections, 

 after having been sufficiently stained, are transferred to and 

 washed in water, then methylated spirit, then in absolute 

 alcohol, then clarified in xylol or clove-oil, and finally 



