THE PLAGUE 117 



ages is shown by the records, but they were overshadowed by the 

 higher mortality of those mentioned above. Improved agriculture has 

 extinguished the fire of St. Anthony, except in the most benighted 

 provinces of Russia. The great fire in London in 1666 destroyed the 

 infected rats and relieved England of the bubonic plague, which had 

 been endemic in that country since 1349. Something more than one 

 hundred years later the discovery of Jenner robbed smallpox of its 

 horrors, wherever vaccination is properly enforced. The investiga- 

 tions of Howard improved the sanitation of jails and workhouses, and 

 did much to eradicate typhus. 



Bacillus. This was discovered and isolated by Yersin and Kitasato 

 independently in the epidemic in Cochin China, and at Hongkong 

 (1893-94). Since the descriptions given by these investigators did 

 not agree in every detail, it was suggested that the organisms obtained 

 by them are not identical, but subsequent studies have shown that 

 they are only slightly different strains of the same bacterium. The 

 bacillus is a short, plump rod with rounded ends and stains more 

 deeply at the ends than in the middle bipolar staining. In length it 

 varies from 1.5 to 1.7 of a micron and its breadth is about one-third 

 its length. However, it manifests marked morphologic variability, 

 coccus-like forms and long rods being found in the same body, also 

 in the discharge from buboes and in the sputum. The polymorphic 

 growth of this bacillus must be held in mind in making a microscopic 

 diagnosis, which is easily done by an expert. It takes the basic stains, 

 such as methylene blue, quickly and deeply. Gaffky recommends that 

 the dried smear be washed with 0.5 per cent, of acetic acid before the 

 stain is applied. It is non-motile, non-liquefying and may show a 

 mucous capsule. However, this is often not recognizable, unless it 

 be brought out by special methods. In the first description of his find, 

 Kitasato made it a motile organism, but subsequently it was shown 

 that such motility as it may manifest is wholly passive. It is sporeless, 

 but may remain viable in culture for four years. Most pathogenic 

 bacteria have their optimum growth temperature at, or slightly above, 

 that of the animal body. This is not true of the plague bacillus. It 

 grows at the temperature of man's body; otherwise it could not be 

 pathogenic to man ; but in artificial cultures it grows much more rap- 



