EXAMINATION OF STAINED BACTERIA. 19 
(A) If the bacteria are evenly distributed’ and 
properly stained, dry both sides thoroughly between 
filter-paper and mount, film side down..in a drop 
of Canada balsam. Label and preserve. ~ 
2. Gram’s Stain. 
The value of this method depends on the fact that 
the mycoprotein of certain bacteria forms with an 
anilin dye and an iodid a compound insoluble in 
alcohol. There are many bacteria in which such 
an insoluble compound is not formed, and this 
method consequently has considerable diagnostic 
value. 
(a) To a drop of water on a clean cover-glass add 
a very small amount of a culture of Bacillus subtilis. 
(4) To the same drop add a very small amount of 
a culture of Bacillus vulgaris, or any culture that 
does not stain by this method. 
(c) Dry,. fix, and stain for five minutes in anilin 
gentian-violet.’ 
(2) Wash in water. 
(e) Treat with Gram’s solution * for one minute. 
1 In a successful preparation the bacteria are evenly and 
not too thickly distributed over the surface. If too many 
bacteria are present, either a smaller amount of the culture 
must be used, or a little from the first cover-glass must be 
added to another drop of water on a second cover-glass, and 
so on until the proper dilution is reached. 
2 See Appendix, page 171. 
3 Gram’s solution : 
Todin, I part ; 
Potassium iodid, 2 parts ; 
Distilled water, 300 parts. 
