320 BACTERIOLOGY. 



swelling of the lymphatic glands, bloody extravasation 

 into the abdominal walls, serous effusion into the pleu- 

 ra 1 and peritoneal cavities ; the intestine is occasionally 

 hypersemic, the adrenal bodies congested, and the spleen 

 enlarged, often being studded with grayish points, sug- 

 gestive of miliary tubercles. The plague, or pest, ba- 

 cillus is detected in large numbers in the local oedema, 

 the lymph-glands, the blood, and the internal organs. 



As is the case in general with the group of hemor- 

 rhagic septicaemia bacteria, the members of which it 

 resembles in certain other respects, when death does not 

 result promptly after infection there is usually only 

 local evidence of the inoculation, the distribution of the 

 micro-organisms throughout the body being considera- 

 bly diminished. 



Animals that survive inoculation with this organism 

 usually exhibit a certain degree of immunity from sub- 

 sequent infection. 



Nuttall l notes that feeding-experiments have resulted 

 in fatal infection in gray and white rats, house- and 

 field-mice, guinea-pigs, rabbits, hogs, apes, cats, chick- 

 ens, sparrows, and flies. He also calls attention to the 

 fact that flies may live for several days after being in- 

 fected with this organism, and if at liberty to fly about 

 may manifestly infect persons or food-stuffs on which 

 they alight or fall. 



The bacilli apparently lose their virulence after 

 long-continued cultivation under artificial conditions, 

 and it is said that from slowly developing, chronic 

 buboes non-virulent or feebly virulent cultures are 

 often obtained. Variations in the degree of virulence 

 have been observed in different colonies from the same 

 1 Nuttall : loc. cit. 



