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250                 PATHOGENIC BACTERIA.

tion and cultivation by the usual plate method are apt to
fail, because the numerous other organisms in the material
grow much more rapidly.

The best method of isolation seems to be the use of an
animal reagent. It has been said that glanders princi-
pally affects horses and asses. Recent observations, how-
ever, have shown the goat, cat, hog (slightly), field-mouse,
wood-mouse, marmot, rabbit, guinea-pig, and hedgehog
all to be susceptible animals. Cattle, house-mice, white
mice, and rats are immune.

The guinea-pig, being a highly susceptible as well
as a readily procurable animal, naturally becomes the
reagent for the detection and isolation of the bacillus.
When a subcutaneous inoculation of some glanders pus
is made, the disease can be observed in guinea-pigs
by a tumefaction in from four to five days. Somewhat
later this tumefaction changes to a caseous nodule, which
ruptures and leaves a chronic ulcer with irregular mar-
gins. The lymph-glands speedily become involved, and
in a month to five weeks signs of general infection are
present. The lymph-glands suppurate, the testicles un-
dergo the same process, and still later the joints exhibit
a suppurative arthritis containing the bacilli. The ani-
mal finally dies of exhaustion. In guinea-pigs no nasal
ulcers form. In field-mice, which are even more suscepti-
ble, the disease is much more rapid. No local lesions
are visible. In two or three days the animal seems un-
well, the breathing is hurried, it sits still with closed
eyes, and without any other preliminaries tumbles over
on its side, dead.

From the tissues of the inoculated animals the pure
cultures are most easily made. Perhaps the best places
to secure the culture are from softened nodes which have
not ruptured or from the suppurating joints. Strauss
has, however, given us a method which is of great use,
because of the short time required. The material sus-
pected to contain the glanders bacillus is injected into
the peritoneal cavity of a male guinea-pig. In three or