5s6 Plague 



3. Hemorrhages beneath the skin and in the internal organs are 

 very suggestive. 



4. Pleural effusion. 



In putrid rats, bubo, granular liver and pleural effusion may persist 

 and are of great significance. A microscopical examination of 

 scrapings from buboes and spleen and inoculation tests will clinch 

 the diagnosis (Besson). 



Virulence. — By frequent passage through animals of the same 

 species the bacillus can be much increased in virulence. KoUe 

 recommended rats for this purpose, and, indeed, declared that 

 without the use of rats it is impossible to keep cultures at a high 

 grade of virulence. According to the researches of the Advisory 

 Committee for the study of plague in India, this is an error. The 

 virulence of plague bacilli for rats is subject to very little change. 

 Their members in investigating the question made twenty-six 

 passages from rat to rat, by subcutaneous inoculation, during 

 eighty-nine days, and found the original virulence of the organism 

 unchanged. 



Yersin found that when cultivated for any length of time upon 

 culture-media, especially agar-agar, the virulence was rapidly lost 

 and the bacillus eventually died. On the other hand, when con- 

 stantly inoculated from animal to animal, the virulence of the 

 bacillus is much increased. 



Knorr, Yersin, Calmette, and Borrel* have shown that the 

 bacillus made virulent by frequent passage through mice is not in- 

 creased in virulence for rabbits. 



This no doubt depends upon the sensitivity of the bacillus to 

 the protective substances of the body juices, immunization against 

 those of one animal not necessarily protecting the organism against 

 those of other animals. 



Sanitation. — A disease that may be transmitted from man to 

 man by atmospheric infection and inhalation, that can be transported 

 from place to place by fomites, that occurs in epidemic form among 

 the lower animals as well as among men, and that can be trans- 

 mitted from man to man and from lower animals to man by biting 

 insects, must inevitably become a source of anxiety to the sanitarian. 



The preventive measures must take account of men, rats, and 

 goods. If vessels are permitted to visit and leave plague-stricken 

 ports, means must be taken to see that all passengers are healthy 

 at the time of leaving and have remained so during the voyage, and 

 provision should be made at the port of entry for the disinfection 

 of the cargo before the goods are landed. But the rats must be 

 given special consideration, for, so soon as the vessel reaches port 

 some of them jump overboard and swim to the shore, carrying the 

 disease with them. When a vessel visits a plague port, every pre- 

 caution should be taken to prevent the entrance of rats, first by 

 * "Ann. de I'Inst. Pasteur.," July, 1895. 



