in ANALYSIS OF PLAGUE MATERIALS 49 



case of plague rests practically on the bacterioscopic dia- 

 gnosis, and it therefore behoves the bacteriologist to have 

 his data resting on a firm basis : the morphological, 

 cultural, and experimental evidence must be clear and 

 decisive. Such evidence is not difficult to obtain if all 

 the steps above detailed are taken with care and circum- 

 spection, and not the least important part of the analysis 

 is, or should be, the culture test and the cutaneous or sub- 

 cutaneous inoculation of the mouse or rat or guinea-pig. 

 A single colony which, in a plate cultivation, complies 

 both in general aspect and constitution with the characters 

 of a colony of the true B. pestis, and which, inoculated 

 cutaneously into the mouse or rat, subcutaneously into 

 the guinea-pig, causes, as it should, an acutely fatal 

 disease with the presence in great numbers of typical 

 B. pestis in the bubo and spleen, is perfectly sufficient to 

 ensure correct diagnosis of " plague." 



A third point which ought to be here mentioned is 

 this : when plate cultivations are made of material which 

 is obtained by puncture from a bubo, i.e. from a sub- 

 cutaneous inflamed swelling, there occur not infrequently 

 one or more colonies which appear as small, grey, trans- 

 lucent, flat discs, with a central slight thickening due to 

 an opaque granule ; these colonies are somewhat slow in 

 their growth, and have a crenated or slightly angular 

 margin. When touched with the point of a platinum 

 needle they are found to be composed of a somewhat 

 cohesive material, they do not well emulsify in saline 

 solution, and when looked at under the microscope are 

 composed of non-motile bacilli more or less connected in 

 strings and masses. When stained they do not show 

 bipolar character, moreover are in shape diphtheroid, i.e. 



E 



