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440                 PATHOGENIC BACTERIA.

for experimental purposes into a plague district, and
kept carefully isolated, died spontaneously of the disease,
presumably because of insect infection.

Yersin found that when cultivated for any length of
time upon culture-media, especially agar-agar, the viru-
lence was rapidly lost and the bacillus eventually died.
On the other hand, when constantly inoculated from
animal to animal the virulence of the bacillus is much

The bacillus probably attenuates readily. Kitasato
found that it did not seem able to withstand desicca-
tion longer than four days; and Yersin found that al-
though it could be secured from the soil beneath an
infected house at a depth of 4-5, the virulence
of such bacilli was lost

Kitasato found that the bacillus was killed by two
hours' exposure to 0.5 per cent, carbolic acid, and also
by exposure to a temperature of 80 C. Ogata found
that the bacillus was instantly killed by 5 per cent, car-
bolic acid, and in fifteen minutes by 0.5 per cent, carbolic
acid. In o. i per cent, sublimate solution it is killed in
five minutes.

It seems possible to make a diagnosis of the disease in
doubtful cases by examining the blood, but it is admitted
that a good deal of bacteriologic practice is necessary for
the purpose.

Abel finds that the blood may yield fallacious results
because of the rather variable appearance of the bacilli,
which are sometimes long and easily mistaken for other
bacteria. He deems the best tests to be the inoculation
of broth-cultures and subsequent inoculation into ani-
mals, which he advises should have been previously
vaccinated against the streptococcus. Plague bacilli
persist in the urine a week after convalescence.

Wilson, of the Hoagland Laboratory, found the thermal
death-point of the organism was one or two degrees
higher than that of the majority of pathogenic bacteria
of the non-sporulating variety, and that, unlike cholera,