THE BACILLUS OF BUBONIC PLAGUE. 311 



" Great Plague of London " of the seventeenth century, 

 though it is difficult to say to what extent these pesti- 

 lences were uncomplicated manifestations of genuine 

 bubonic plague. During the existence of the Justinian 

 Plague 10,000 people are said to have died in Con- 

 stantinople in a single day, and Hecker estimates that 

 during the pandemic of the Black Death 25,000,000 

 people (a quarter of the entire population of Europe) 

 succumbed to the disease. During the Great Plague 

 of London (1664-'65) the total mortality for one year 

 was 68,596, out of an estimated population of 460,000 

 souls. 



It is not surprising to learn that it was to guard 

 against the plague that quarantine regulations were 

 first established. 



The first and certainly the most exact information 

 up to date concerning the cause and pathology of the 

 plague resulted from the investigations of Yersin, of 

 Kitasato, and of Aoyama, conducted during the epi- 

 demic of 1894 in Hong-Kong, China; although since 

 then numerous other investigators have made addi- 

 tional important contributions to our knowledge of 

 the subject. The results of these studies demonstrate 

 that bubonic plague is an infectious, not markedly con- 

 tagious, disease that depends for its existence upon the 

 presence in the tissues of a specific micro-organism — 

 the so-called plague or pest bacillus. 



This organism is described as a short, oval bacillus, 

 usually seen single, sometimes joined end to end in pairs 

 or threes, less commonly as longer threads. It stains 

 more readily at its ends than at its centre. It is some- 

 times capsulated ; is non-spore-forming ; is aerobic, and 

 is non-motile. It is found in large numbers in suppu- 



