xi] BACILLUS: PATHOGENIC FORMS. 163 



centimetre of a concentrated alcoholic solution of methylene- 

 blue is mixed with 200 ccm. of distilled water; to this are 

 added two ccm. of a 10 per cent, solution of caustic potash. 

 In this solution the fresh or hardened sections or particles of 

 tubercles are kept for half an hour if heated up to 40 C, or for 

 twenty-four hours if not heated. . After this the preparation 

 is stained for two minutes in a filtered concentrated watery 

 solution of vesuvin, then washed in distilled water. On ex- 

 amination with a -^ oil immersion lens and Abbe's condenser 

 it will be found that all the elements are stained brown with 

 vesuvin except the bacilli, which are blue. A still more suc- 

 cessful and more delicate reaction is shown by the bacilli if 

 the preparation is stained after Ehrlich's method. About 

 5 ccm. of pure anilin (anilin oil) are well mixed with 100 ccm. 

 of distilled water and filtered ; to this is added a saturated 

 alcoholic solution of fuchsin, and with this the preparation is 

 stained for a quarter to half an hour. It is then washed for 

 a few seconds in a mixture of one part of nitric acid and two 

 parts of water, and then is well washed in distilled water. 

 The preparation when now examined shows no trace of 

 colour except in the tubercle-bacilli, which retain the red 

 colour of the fuchsin. The tissue may now be stained either 

 with vesuvin or methylene-blue, which makes the ground- 

 work brown or blue, but the bacilli remain red. This reaction 

 after washing with nitric acid is exceedingly delicate, and is 

 perfectly characteristic and trustworthy, as all putrefactive 

 organisms become discoloured by the washing with nitric 

 acid, the tubercle-bacilli only retaining the colour. There 

 are other methods which are very good ; those of Weigert and 

 of Gibbes l are very quick and trustworthy in their action. 



Weigert has devised a staining fluid which gives very beau- 

 tiful results and is very useful for staining sections, fresh or 

 1 Lancet, August 5, 1883. 



M 2 



