190 TECHNOLOGY OF BACTERIA. 



recommends the following method. After stain- 

 ing with an aniline color, soak the sections in a 

 weak solution of carbonate of potash, instead of 

 acetic acid. By this means the animal tissues, 

 including nuclei and plasma cells, lose their color, 

 while the bacteria alone remain stained. 



Staining the Tubercle- Bacillus. The following 

 method was first recommended by Koch : One 

 cubic centimetre of a concentrated alcoholic solu- 

 tion of methyl-blue is added to two hundred 

 cubic centimetres of distilled water, and well 

 shaken ; then add, under continuous shaking, two 

 tenths cubic centimetres of a ten per cent solution 

 of caustic potash. The cover-glasses upon which 

 tuberculous sputum has been spread and dried, 

 or thin sections of a tuberculous lung, etc., are 

 left in this solution for twenty-four hours. If the 

 solution is heated in a water-bath at 40 C., the 

 staining will be effected in much less time, half 

 an hour to an hour. The preparation is next 

 treated with a concentrated aqueous solution of 

 visuvin, which should be filtered just before it is 

 used. After one or two minutes this is washed 

 off with distilled water. 



The visuvin solution discharges the blue color 

 from the cells, nuclei and tissue elements goner- 

 ally, giving them a brown color, while the tuber- 

 cle-bacilli retain their blue color and are readily 

 recognized. 



