CHAPTEK II 



CHARACTERS OF THE BACILLUS PESTIS 



(A) Morphology. — The plague bacillus is a non -motile 

 rod, of a short oval to cylindrical shape, possessed of 

 rounded ends, and measuring in dried or stained film 

 specimens of the tissues on an average from 0'8 /* to 1*6 /*. 

 in length, 0*4 n to 0*8 /jl in thickness. Measurements which 

 I made of various races show that the longest bacilli 

 occur in the bubo of the rat spontaneously dead of the 

 plague ; these bacilli are at the same time well rounded, 

 almost slightly tapering at the ends. Next in size are 

 those of the bubo of man affected with plague, presumably 

 through the rat. 



The B. pestis stains readily with all the aniline dyes 

 usually employed for staining bacteria ; the only special 

 feature about the staining of the B. pestis is that when 

 taken from tissues — film specimens — and subjected to 

 particular staining, most individuals show within a deli- 

 cately stained sheath a marked bipolar arrangement of 

 the stained or chromatic substance, i.e. rods, short or long, 

 with rounded ends, and showing a stained mass at each 

 end, whereas the middle part is clear and not stained ; 

 that is to say, the chromatic substance is limited to the 



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