i] MICROSCOPIC EXAMINATION 15 



some instances this is not easy of achievement, since by 

 such decolourising processes also the bacteria are liable to 

 lose the stain, it nevertheless is possible in the majority of 

 instances. In many cases prolonged washing in alcohol 

 absolutus and in clove-oil is sufficient to abstract the dye 

 from the tissue-elements, but in some special cases, owing to 

 peculiar chemical properties possessed by certain bacteria, 

 the decolourising process requires special methods. Of these 

 the following are the most useful : — 



I. In some instances the specimens (cover-glass specimens 

 and particularly sections) are stained in one dye, then 

 washed in alcohol till quite pale, then transferred to a 

 contrast dye. As contrast dyes are to be regarded blue 

 and red, or red and brown, or blue and brown, or violet 

 and brown. In some cases only the bacteria retain the first 

 dye, the tissue-elements become stained by the second dye. 

 A similar result is often obtained by mixing the two dyes, 

 and then using them like a single dye ; hereby occasionally 

 the bacteria are found to take one colour, while the tissue- 

 elements take the contrast dye. 



For double-staining, of film specimens or sections the 

 following methods will be found most practicable for 

 general purposes : — (a) As a first stain methyl-blue aniline 

 water is used ; after well staining the specimen it is well 

 washed in water and then placed in ^ per cent, alcoholic 

 solution of eosin for from half to one minute, then washed 

 in water and prepared for mounting in balsam as usual ; (d) 

 a 2 per cent, watery solution of rubin is used as first dye, 

 then well washed in water, then placed in methyl-blue 

 aniline water for half to one minute, washed in water and 

 proceeded in the usual manner for balsam mounting. 



The number of methods for successfully and differentially 

 double and treble staining normal and pathological tissues 

 is legion, and those who consult the excellent books by 



