94 PA THOGENIC BA CTERIA.

two to three minutes; 5. Wash thoroughly in water;
6. Dry; 7. Mount in Canada balsam.

This simple process suffices to stain most bacteria.

Ohlmacher1 deserves credit for his observation that
when the u fixed " preparation is immersed for a moment
or two in a 2-4 per cent, solution of formalin, the brill-
iancy of the stain is considerably increased.

Staining Bacteria in Sections of Tissue. — It not
infrequently happens that the bacteria to be examined
are scattered among or enclosed in the cells of tissues.
Their demonstration is then a matter of some difficulty,
and the method employed is one which must be modified
according to the kind of organism to be stained. Very
much, too, depends upon the preservation of the tissue
to be studied. As bacteria disintegrate rapidly in dead
tissue, the specimen for examination should be secured
as fresh as possible, cut into small fragments, and im-
mersed in absolute alcohol from six to twenty-four hours
to kill the cells and bacteria. Afterward they are re-
moved from the absolute alcohol and kept in 80-90
per cent, which does not shrink the tissue. Bichlorid
of mercury may also be used, but absolute alcohol seems
to answer every purpose.

The ordinary methods of imbedding suffice. The sim-
pler of these are probably as follows:

I. Celloidin.—From the hardening reagent (if other
than absolute alcohol)—

12-24 hours in 95 per cent, alcohol,

6-12 tl u absolute alcohol,
12-24 u u ^hin celloidin (consistence of oil),

6-12 u u thick celloidin (consistence of molasses).

The solutions of celloidin are made in equal parts of
absolute alcohol and ether.

Place upon a block of dry wood, allow to evaporate
until the block can be overturned without dislodging the
specimen ; then place in 70-80 per cent alcohol until

1 Medical News, Feb. 16, 1896.