PATHOGENIC BACTERIA
the cholera spirillum, and also of making a diagnosis
of the disease in a suspected case, is probably that of
Schottelius. The method is very simple : A small quan-
tity of the fecal matter is mixed with bouillon and stood
in an incubating oven for twenty-four hours. If the

fig. 82.—Spirillum of Asiatic cholera: colonies two days old upon a gelatin
plate;   x 35 (Heim).
cholera spirilla are present, they will grow most rapidly
at the surface of the liquid when the supply of air is
good. A pellicle will be formed, a drop from which,
diluted in melted gelatin and poured upon plates, will
show typical colonies.
Under the microscope the principal characteristics
can be made out. The colony of the cholera spirillum
scarcely resembles that of any other organism. The little
colonies which have not yet reached the surface of the
gelatin begin very soon to show a pale-yellow color and
to exhibit irregularities of contour, so that they are
almost never smooth and round. They are coarsely
granular, and have the largest granules in the centre.
As the colony increases in size the granules also increase