Pathogenic Bacteria

METHODS OF OBSERVING BACTERIA. 93

For ordinary staining an aqueous solution made in a
simple manner is employed. A small bottle is nearly
filled with distilled water, and the stock-solution is added,
drop by drop, until the color becomes just sufficiently in-
tense to prevent the ready recognition of objects through
it. Such a watery solution possesses the power of readily
penetrating the dried protoplasm of the bacterium, taking
the stain with it. Alcohol does not have this power.

As in the process of staining the cover is apt to slip
from the fingers and spill the stain, it is well to be pro-
vided with cover-glass forceps (Fig. 8), which hold the

FIG. 8.—Stewart's cover-glass forceps.

glass in a firm grip and allow of all manipulations with-
out danger to the fingers or clothes. The ordinary in-
struments are entirely unfitted for the purpose, as capil-
lary attraction draws the stain between the blades and
makes certain the soiling of the fingers. Sufficient stain
is allowed to run from a pipette upon the smeared side
of the cover-glass to flood it, but not overflow, and is
allowed to remain for a moment or two, after which it
is thoroughly washed off with water. If the specimen
is one prepared for temporary use, it can be examined at
once, mounted in a drop of water, but under these con-
ditions will not appear as advantageously as if dried and
then mounted in Canada balsam.

Sometimes the material to be examined is too solid to
spread upon the glass conveniently. Under such circum-
stances a drop of distilled water can be added and a minute
portion of the material be mixed in it upon the glass.

The entire process is, in brief:

i. Spread the material upon the cover ; 2. Dry—do not
heat; 3. Pass three times through the flame ; 4. Stain