THE BACILLUS OF PLAGUE. 113 



jection, become susceptible when they are starved or fatigued, 

 and pigeons if food is withheld lose their natural resistance to 

 plague (28). Although the pest-bacillus is pathogenic for a 

 large number of animals it is by no means proved that 

 during an epidemic they actually convey the disease, though, 

 of course, this is conceivable. Hankin (23) has shown that 

 there is no necessary connection between infection of 

 animals and outbreaks among men. In many localities near 

 Bombay after the disease had been introduced by human 

 beings, it ran its course without a single rat being affected, 

 and in the neighbourhood of Hurdwar a genuine outbreak 

 occurred among rats and terminated without spreading to 

 the community. 



In the bodies of plague-stricken individuals specific 

 microbes can be easily recognised in the glandular 

 swellings, in pus and the blood. Their presence in the 

 latter affords a certain means of diagnosis in doubtful cases, 

 but since comparatively few pest-bacilli are met with in blood 

 a large number of specimens must be made and care taken 

 not to mistake those which are seen for streptococci which 

 are not infrequently present. By blood examination Lowson 

 found the pest-bacillus in 80 per cent, of cases and Wilm 

 in 77 per cent. The latter observer considers that a more 

 certain diagnosis may be obtained by cultivating the sus- 

 pected blood in bouillon, and has also recommended an 

 examination of the urine which always contains plague- 

 bacilli, not only during the disease but for at least a week 

 after recovery. Two members of the Russian Plague 

 Commission (24) have also shown that the blood serum of 

 patients convalescent from plague has the power of causing 

 an agglutination of the bacilli in a hanging drop or bouillon 

 culture, similar to that originally observed by Chantermesse 

 and Widal when the blood of patients suffering from 

 typhoid-fever was added to cultures of bacillus typhosus or 

 the serum of cholera to cholera microbes. This phenomenon 

 of agglutination in cases of plague is not seen during the first 

 week, but appears by the seventh day, persists until the 

 fourth week and then finally is lost. The members of the 



German Plague Commission (25) have also noted this re- 



8 



