200 BACTERIOLOGY. 
should be kept completely covered with fluid. The 
bacteria having now been stained, the cover-glass is 
grasped in the forceps and thoroughly washed in clean 
water and then dried, first between layers of filter-paper 
and then in the air. A drop of balsam or water is now 
placed on a glass slide and the cover-glass placed upon 
it with the bacterial side down. The preparation is 
now ready for microscopical examination. 
The Preparation of Sections. Occasionally it is of value 
to examine the bacteria as they are in the tissues them- 
selves. These should be obtained as soon as possible 
after death, so as to prevent any post-mortem changes 
or increase of the bacteria in them. From the properly 
selected spots small portions, not larger than one cubic 
centimetre, are removed and placed in absolute alcohol 
to harden. These portions, when of nearly the con- 
sistency of fresh, solid rubber, are removed, and, if the 
nature of the tissues will allow, fastened to corks or 
pieces of hard rubber by mucilage. After drying, the 
specimens are replaced in alcohol for twenty-four hours 
and then cut into thin sections with the microtome. 
Sometimes the tissues do not become sufficiently dense 
by this simple method; they must then undergo the 
process of embedding in celloidin or paraffin. 
The Ordinary Staining Solutions. Simple staining is 
used for the demonstration of bacteria in general, and 
is also useful for gaining an idea of the other elements in 
the preparation. The solutions commonly employed in 
staining bacteria are the watery solutions of basic aniline 
dyes—fuchsin, gentian-violet, and methylene - blue. 
These solutions may either be prepared by dissolving 
the dyes directly in water, or, more usually, by having 
stock saturated alcoholic solutions of them, from which 
