THE METHODS OF STAINING MICROBES 71 



cover-glass preparation should be floated for half 

 an hour on the surface of a small quantity of hot 

 magenta and aniline stain. 1 The magenta is dis- 

 charged from the bacilli by washing in water, in 

 alcohol, or weak nitric acid, according to the species. 

 The preparations are then treated (for three or four 

 minutes) in a solution of methylene blue, and 

 finally washed with water, drained, dried, and 

 mounted in Canada balsam or other mounting 

 media. By this method the spores are stained red, 

 while the bacilli are blue. 



Koch's method for staining tubercle bacilli is as 

 follows: Cover-glass preparations of the sputum, 

 etc., are placed in a solution containing 1 part of a 

 concentrated solution of methylene blue, 2 parts of 

 a potash solution (10 per cent.), and 200 parts of dis- 

 tilled water. The preparations remain in the solution 

 (heated to 40 C.) for twenty-four minutes. They 

 are then washed in water, and placed in an aqueous 

 solution of vesuvin for two or three minutes ; again 

 washed, and subsequently treated with alcohol, oil 

 of cloves, and finally mounted in Canada balsam. 

 Koch's method stains the bacilli blue, and the 

 nuclei, etc., brown. ' All the other forms of bacteria 

 which Koch has as yet examined in this way are 

 stained brown, with the exception of the bacilli 

 found in leprosy, which also retain the methylene 

 blue in preference to the vesuvin. These bacilli 



1 This stain is prepared by mixing together 5 cc. of aniline 

 oil and 100 cc. of distilled water. The mixture is filtered, and 

 to the filtrate is added a concentrated alcoholic solution of 

 fuchsine or magenta, until a precipitate begins to ba formed. 



