v PLAGUE IN THE EAT 103 



In connection with these later experiences I am dis- 

 posed to consider that what Kitasato first described as B. 

 pestis was after all B. pestis, though of the (b) type. I 

 myself once received from Dr. Atkinson of Hong-Kong a 

 culture, originally received from Kitasato, which belonged 

 to this type. It was a coccus-like oval bacillus of very 

 slight virulence, practically not fatal to rodents, and its 

 colonies were very translucent or colon -like. Kitasato's 

 coccus-like bacillus was, it will be remembered, denied the 

 rank of B. pestis on account of its low pathogenicity ; but 

 for the above reasons I believe it to stand on the same 

 footing as Edington's rat bacillus. 



2. Bubonic Plague artificially induced in rats. — The 

 white rat is just as, in fact more, susceptible to infection 

 with plague as the brown or wild rat. For this reason I use 

 for experiment the former in preference to the latter. It 

 is easier kept in the laboratory, it is easier handled, and, 

 unlike the wild rat, of which when in captivity a large 

 percentage die spontaneously, it thrives and breeds well 

 in captivity. All my experiments on the rat therefore 

 invariably, unless otherwise stated, refer to the white or 

 tame rat. 



The rat being, as has been said, highly susceptible of 

 plague, is easily infected in a variety of ways ; the 

 simplest is by subcutaneous injection or by cutaneous 

 inoculation. This latter mode is undoubtedly that by 

 which plague bacilli can be differentiated with certainty 

 from any other similar microbes. It was first introduced 

 by Albrecht and Gohn (Austrian Plague Commission), and 

 it is a method by which infection with plague can be 



rat plague, being few and far between ; plague imported by rats seldom makes 

 progress as an epidemic. 



