CHAPTER XXIX. 

 BACILLUS PESTIS. 



Introduction. 



Section I. The experimental disease, p. 463. 



Section II. Morphology, p. 464. 



1. Microscopical appearances and staining reactions, p. 464. 2. Cultural charac- 

 teristics, p. 465. 



Section III. Biological properties, p. 466. 



1. Vitality and virulence, p. 466. 2. Bio-chemical reactions, p. 467. 3 Toxins, 

 p. 467. 4 Vaccination, p. 468. 5. Serum therapy, p. 471. 6. Agglutination, 

 p. 472. 7. Precipitins, p. 473. 



Section IV. Isolation and identification of the plague bacillus (including an account of 

 the post mortem appearances in the naturally infected rat), p. 473. 



THE bacillus of plague was discovered in 1894 by Yersin [and Kitasato 

 independently]. 



In the human subject plague may assume one of two forms, bubonic or pneumonic ; 

 of the two the former is the more common. [In both forms a septicaemia may occur, 

 generally as a late symptom, but it is incorrect to speak of a septicsemic as opposed 

 to a bubonic and a pneumonic form (Simond).] 



In bubonic plague the bacillus is present in the pus of the lymphatic glands and 

 occasionally in the blood and more rarely in the stools (Wilm). [In India the 

 Advisory Committee x found that in a large proportion of cases (67 per cent.) the 

 bacillus is present in the blood and that a bacilluria occurs in about 30 per cent, of 

 cases. In bubonic plague it is not uncommon for a secondary pneumonia to 

 develop.] 



In the pneumonic form, though there is an absence of buboes, the bacillus is 

 present in the lymphatic glands. It is frequently present in the blood and always 

 in the sputum (Metin indeed demonstrated the presence of bacilli in the sputum of 

 plague patients a week after the temperature had fallen to normal, but could detect 

 them only by inoculation and found their virulence was attenuated) ; bacilli can 

 also be found in the juice and in sections of the lung and spleen (Tchistowitch). 



According to Haffkine the native races of India are more susceptible to plague 

 than are either white people or the native races of Africa. 



In epidemics of plague, rats are, as a rule, the first to suffer. " Plague 

 which is at first a disease of rats soon becomes a disease of man " (Roux and 

 Yersin). 



[Besides its occurrence in rats natural plague has been observed in guinea-pigs 

 in India (Indian Commission); in rabbits in India (Indian -Commission) and in 

 England (Martin and Rowland) ; in apes Cynopithecus niger and monkeys 



[* The reports on plague investigations in India issued by the Advisory Committee 

 appointed by the Secretary of State for India, the Royal Society and the Lister Institute 

 are published in the Journal of Hygiene, 1906, 1907, 1908 and 1910.] 



