i THE ESSENTIAL CAUSE 5 



when examined by film specimens, showed each field of the 

 microscope literally crowded with the bacilli. 



While, then, in the acute cases, the microscopic ex- 

 amination of the bubo material enables one to make the 

 preliminary diagnosis " plague most probable," it is not so 

 in the chronic cases, i.e. in pestis minor, or in ambulating 

 plague, when the buboes suppurate and become converted 

 into open discharging sores, for here the material in 

 microscopic specimens may, and generally does, show a 

 variety of microbes, (a) Foremost among these one finds 

 cocci, which by culture are shown to be either Staphylo- 

 coccus albus or aureus ; they are Gram-positive ; (b) next 

 one finds streptococci ; they are Gram-positive ; these are 

 less common ; (c) here and there a diphtheroid bacillus, 

 Gram-positive, which by culture is shown to belong to 

 the xerosis group ; (d) bacilli with round ends, 

 and showing on staining more or less distinct bipolar 

 character : these may be B. proteus, B. coli, or B. pestis, 

 all being Gram-negative. The culture test, however — 

 surface agar plates at 37° C. incubated, — shows already in 

 twenty-four hours the differentiation in a marked manner ; 

 these differences will be dealt with fully later in a special 

 chapter. 



I have in the course of the last nine years examined a 

 large amount of material of inguinal, femoral, axillary, and 

 cervical swellings which had been associated with febrile 

 symptoms, and there being, on epidemiological grounds, a 

 possibility of such disease being plague — the persons being 

 either in a port or had arrived in a ship which had come from 

 or had touched an infected port — the material was subjected 

 to careful bacteriological analysis, with the result that 

 plague was negatived, and, as the further history proved, 



