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348 it is found in the follicles themselves, in the lymph spaces, and in the medullary cords (Aoyama). If death has taken place at a very early stage of the disease, the swelling of the lymphatic glands may not be so evident ; but it is rare not to find some gland or glands characteristically affected. In those septicæmic and pneumonic cases in which the bubo is absent nearly all the lymphatic glands of the body are slightly enlarged, pink or dark red in colour. Sometimes the lymphatic trunks are also markedly implicated.

Diagnosis.— The occurrence of fever and adenitis during a plague epidemic must invariably be viewed with suspicion, and particularly if the fever rapidly assumes an adynamic character. In the early stages diagnosis may be very doubtful, especially in pneumonic plague, and in countries of high filarial endemicity and in which filarial adenitis is necessarily a common occurrence. The discovery of the bacillus in the glands, blood, sputum, or discharges is the only thoroughly reliable test. A small quantity of the suspected material should be spread on a slide, dried, fixed, and stained with an aniline dye. Should a cocco-bacillus be found with the characteristic bipolar staining, it should be cultivated by Haffkine's method in broth on which clarified butter (ghee) or coco-nut oil is floated. From the under-surface of the oil, if the bacillus be that of plague, stalactite-like growths of bacilli will form. When disturbed, the stalactite growths break off and fall in snow-like flakes to the bottom of the vessel. No other known bacillus behaves in this way. (See p. 325.) In case of doubt, animal inoculation should be had recourse to: a little of the virus from the patient or a culture is rubbed into a shaven area (1 in. square) on the abdomen of a white rat or a guineapig. B. pestis inoculated in this way kills the guineapig in seven days, the rat sooner.*