Pathogenic Bacteria

CULTURES, AND THEIR STUDY. 147

is removed cautiously ; the wire bearing the bacteria
from the colony is introduced until its point enters the
centre of the gelatin, and is then carefully pushed on
until a vertical puncture from the surface to the bottom
of the gelatin is made. This is the puncture-culture—
u stichcultur " of the Germans.

If the bacteria are only to be planted upon the surface
of the culture-medium, the wire is drawn over the surface
of a tube of obliquely solidified gelatin, agar-agar, blood-
serum, etc. with a steady, slow movement, so as to scatter
the germs along its path and cause the development of
the bacteria in an enormous colony or mass of colonies
in a line following the longest diameter of the exposed
surface from end to end. This is the stroke-culture—
u strichcultur."

The method of holding the tubes, cotton plugs, and
platinum wire during the process of inoculation is shown
in Figure 20.

Sometimes it is desirable to preserve an entire colored
colony as a microscopic specimen. To do this a perfectly
clean cover-glass, not too large in size, is momentarily
warmed, then carefully laid upon the surface of the
gelatin or agar-agar containing the colonies. Sufficient
pressure is applied to the surface of the glass to exclude
bubbles underneath, but the pressure must not be too
great, as it may destroy the integrity of the colony.
The cover is gently raised by one edge, and if successful
the whole colony or a number of colonies, as the case
may be, will be found adhering to it. It is treated
exactly as any other cover-glass preparation, is dried,
fixed, stained, and mounted, and kept as a permanent
specimen. It is called an adhesion preparation—u klatsch
praparat.''

Very often, when one is in a hurry, pure cultures from
single colonies may be secured by a very simple manipu-
lation suggested by Baiiti.1 The inoculation is made
into the water of condensation at the bottom of an agar-

1 Centralbl, f. Bakt. imd Parasitenk.y 1895, xvii., No. 16.