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104                 PA THOGENIC BA CTERIA.

covered with the hot stain is laid aside for a minute, then
washed in water and mounted. In such preparations I
have always been able to see the fkgella well, but usually
find that while the flagella are very distinct, the bodies
of the bacteria are scarcely visible.

Bunge suggests a mordant consisting of a concentrated
aqueous tannin solution and a i : 20 solution of liq. ferri
sesquichloridi in water. The best mixture seems to be
3 parts of the tannin solution to i part of the diluted
iron solution. To 10 of this mixture i of a
concentrated aqueous fuchsin solution is added. It is
not necessary to prepare this mordant fresh for each
staining, as it seems to improve with age. The use of
acid and alkaline solutions added to the mordant is dis-
pensed with.

The bacteria are carefully fixed to the glass, stained
with the mordant for five minutes, wanning a little to-
ward the end, washed, dried, and subsequently colored
with carbol-fuchsin warmed a little.

Bacteria can best be measured by an eye-piece microm-
eter. As these instruments vary somewhat in con-
struction, the unit of measurement for each objective
magnification or the method of manipulating the adjusta-
ble instruments must be learned from dealers' catalogues.

Photographing bacteria requires special apparatus and
methods, which are fully described in text-books upon
the subject.