INTRODUCTION 



XV 



actually found to be so, while other similar cases were 

 proved bacteriologically not to be cases of plague. 

 Such cases, although clinically suspected to be plague, 

 were, in confirmation of the negative bacteriological 

 evidence, not followed by any further cases of the 

 disease. The same applies to rats ; for while, on the one 

 hand, bacteriological analysis confirmed the preliminary 

 diagnosis made by the sanitary authority, viz. that 

 mortality amongst rats on certain ships coming from 

 infected ports was due to plague, it has, on the other 

 hand, shown that mortality of rats on ships need not 

 necessarily be due to plague, because rats are subject 

 also to several forms of acute infectious maladies other 

 than plague. 



During the last ten years I have had a good many 

 opportunities of investigating bacteriologically materials 

 of suspected and real cases of plague of human beings and 

 of rats ; I have also made special studies of the B. pestis 

 in its morphological, cultural, and physiological characters, 

 and in the manner of its conveyance and action. Some 

 of these studies have been published in the Annual 

 Eeports of the Medical Officer of the Local Government 

 Board, and are here reproduced, partially or wholly, by 

 permission of the Controller of H.M. Stationery Office. 

 It seems not out of place to collect the results of all these 

 studies, carried on now for a succession of years, in a 

 connected and easily accessible form. The following 

 pages are devoted to this purpose. 1 



1 With the exception of Fig. 1, all the illustrations are photograms made for me 

 by Mr. Albert Norman, M.R.C.S., London. 



