The Microscope. 189 



as in making a balsam mount. When carefully done, not a ves- 

 tige of the scratches can afterwards be detected. A large and 

 costly prism belonging to an instrument of mine, having been 

 badly scratched by the careless handling of a student, was sent 

 to a local lapidary, who repolished it. On the return of the 

 piism from the hands of the polisher, I found that its optical 

 properties had been sadly interferred with from the fact that in 

 the process of polishing the surface had been cut away more at 

 some points than at others, thus causing it to give a distorted 

 image of objects regarded through it. By resorting to the above 

 process, however, and cementing a cover-glass to each end. I 

 found that its pristine virtues were restored, and that it now 

 works as well as it ever did. 



A MODIFIED METHOD OF STAINING THE BACILLUS 

 TUBERCULOSIS. 



According to the Deutsche Militair-Aerztliche Zeitung the 

 following method of staining the bacillus is taught the medical 

 officers of the army in the courses of instruction at Bonn. 



1. A whitish particle is selected from the sputum and 

 spread in a thin film between two cover-glasses ; these are 

 then separated and the films are allowed to dry. 



2. Aniline-water is prepared as follows : A test-tube is 

 half filled with water and so much aniline-oil added as will just 

 fill the concave bottom of the tube. This mixture is vigorously 

 shaken and filtered through a moist filter. A quantity of this 

 filtrum is poured into a watch-glass and thereto are added eight 

 to ten drops of a concentrated alcoholic solution of fuchsin or 

 of methyl- violet or gentiana- violet. 



3. The dry film of sputum is then drawn through an alco- 

 hol flame, the glass being held by forceps, about four times with 

 moderate velocity. The glass is then floated film-side down 

 upon the solution above described. This is heated to a point of 

 heat at which steam-vapor is liberated for about half a minute. 



4. The specimen is then washed in water and immersed in 

 muriate of alcohol (one part of chemically pure muriatic acid 

 to one-hundred parts of 90 per cent, alcohol) for one-half to one 

 minute. 



