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XX] General prophylaxis.— The prophylaxis of plague, as of other infectious diseases, has to be considered from the standpoint of the community and also from that of the individual. As regards the former, it includes measures for preventing the introduction of the virus, for staying its spread if introduced, and for securing its destruction.

Quarantine.— Modern systems of land or sea quarantine directed against plague take cognizance of the facts that the incubation period of the disease may extend to ten days, and that plague affects certain of the lower animals as well as man. Ten days is the minimum period that should elapse between the time of departure from an infected place, between the date of the last death, or between the arrival of a ship or batch of travellers with cases of plague in progress among them, and the granting of free pratique. Moreover, as Kitasato has shown that the specific bacillus persists in the bodies of those who have recovered from plague for at least three weeks from the cessation of the active disease, convalescents should be isolated for a month before they are allowed to mingle with an uninfected community.

Although Kitasato has stated that the plague bacillus perishes in four days when dried on coverglasses and protected from sunlight, and in from three to four hours when exposed to sunlight, experience has shown that under certain conditions, as yet unknown, it will survive outside the body for a very much longer period.* There is a. considerable mass of evidence tending to show that clothes, skins, recognizable. If the gland is itself inflamed it is almost diagnostic of plague; in which case the liver will be found of a yellow colour and sprinkled with innumerable pinky-white granules. The spleen is enlarged, congested, and occasionally granular. Serous or blood-stained serous effusions are present in 72 per cent, of such rats. If on Microscopical examination of scrapings from glands or spleen bipolar -staining bacilli are detected the case is probably plague. Too great stress must not be laid on bipolar staining, as this feature depends somewhat on the method of staining; it is best demonstrated by Leishman or eosin-azur stain.