AGf~ICULTURAL RESEARCH, PUSA.

868 PRACTICAL BACTERIOLOGY
regurgitation takes place fTom the blocked proventriculus
into the bite wound, and so inoculation results.
The time dtll'ing which a flea remains inrec:tive--Le. the
lleriod of survival of the hacilli--depends on temperature
und humidity. A temperature of about 10 0 C. and a hin'll
degree of humidity have been found by experiment to be
the most suitable conditions.
PneuIUonie plague is communicated from person to
persoll by infected secretion droplets from the respiratory
passages.
DIAGNOSIS
Hnbonic Plague.-The bubo is punctured with a
hypodermic syringe and exudate withdrawn. From
this material, films are made and stained with methylene
blue and by Gram's method. The appearance of
the characteristic bacilli showing bipolar staining is
highly suggestive.
Cultures are also made on nutrient agar, and single
colonies are picked off on to agar slopes. The
resulting cultures are then available for further
investigation.
Some of the exudate should also, if possible, be
injected subcutaneously into a guinea-pig or whitc
rat. If plague bacilli are present, the inoculated
animal will die, showing at autopsy the appearances,
etc., described above.
The cultures obtained may be tested as regal'ds:
biochemicn,l reactions, involution on 13 pel' cent. saltagar,
chain formation in bouillon. and stalactite
growth. The cultUl'es can also be used for further
animal-inoculation experiments.
Pneumonic Plague.-The bacilli can be detected
microscopically in the sputum, and for identification
should be isolated in pure culture as in clealing with
material from bubonic plague.
In carrying out animal inoculation with sputum,
other virulent organisms may be present (e.g. pneumococci);
instead of injecting subcutaneously, successful
inoculation with B. pestis can be effected by applying
the material to the nasal mucosa, 01' to a shaved area
of skin.