NEW METHODS OF USING THE ANILINE DYES. 409 



dropped in, the nuclei and bacteria will be found to have taken the 

 dye. But if the section is placed in an alcoholic solution of 

 fuchsin, and if the dye is precipitated by the addition of a consi- 

 derable quantity of benzine, the whole of the tissue will be found 

 to be strongly stained a uniform crimson tint. The dye has 

 acted as a background stain. From these considerations it is 

 evident that firstly, after the nuclei or bacteria in a section have 

 been stained with Spiller's purple, fuchsin, or gentian violet, if 

 the excess of colour is being removed by means of oil of cloves 

 care must be taken to move the sections into a fresh quantity 

 of the reagent as soon as it has become strongly tinted by the 

 dye. And, secondly, after staining bacteria by double treat- 

 ment with Spiller's purple or methyl blue, they may be contrast 

 stained with fuchsin dissolved in an oily medium. Aniline is 

 the best for the purpose. After leaving in this reagent for 

 about a minute they should be removed to picric acid and clove 

 oil for a few seconds, then washed and mounted. If methyl 

 blue was the dye previously used, the bacteria will be found to 

 be stained green on a brick-red background. 



Another method of staining, which, though a little more 

 complicated seems to offer certain advantages, is as follows : 



Sections are subjected to double treatment with fuchsin as 

 above described, then washed for about five minutes in picric 

 acid dissolved in oil of cloves ; this last reagent is removed by 

 washing in benzine and clove-oil mixture. They are then 

 treated with methyl blue dissolved in aniline oil for about ten 

 minutes. The effect of this is that every structure that was 

 previously stained red with fuchsin is turned black, blue black, 

 or dark purple. This, then, is the colour of the bacteria, and 

 the background tint is green or blue. This can be changed to 

 red by placing the section in oil of cloves and eosin for a 

 minute. The sections are then washed and mounted as in the 

 other methods. Not only do sections stained in this way 

 promise to be remarkably permanent, but the contrast between 

 the dark blue of the micro-organism and the pale pink of the 

 background is as strong as can be desired. 



The question arises whether sections stained by these methods 



