THE BACILLUS OF BUBONIC PLAQUE 415 



Biology. An aerobic, non-motile bacillus. Grows best at 30 to 

 35 C. Does not form spores. Grows on the usual culture media, which 

 should have a slightly alkaline reaction. Does not liquefy gelatin. 

 Grows well on blood-serum media. It grows rapidly on glycerin agar, 

 forming a grayish-white surface growth. The bacilli appear, as a rule, as 

 short, plump, oval bacilli, but a few present elongated thread forms which 

 are very characteristic. In bouillon a very characteristic appearance 

 is produced, the culture medium remaining clear while a granular or 

 grumous deposit forms on the walls and on the bottom of the tube. In 

 bouillon and most fluid media the growth is in the form of short or 

 medium chains of very short, oval bacilli, which look almost like strepto- 

 cocci. 



Pathogenesis. This bacillus is pathogenic for rats, mice, guinea- 

 pigs, monkeys, rabbits, flies, and other insects, which usually die within 

 two or three days after inoculation. Then at the point of inoculation 

 is found a somewhat hemorrhagic infiltration and oedema, with enlarge- 

 ments of the neighboring lymph glands, hemorrhages into the peri- 

 toneal cavity, and parenchymatous congestion of the organs. The 

 spleen sometimes shows minute nodules resembling miliary tubercles. 

 Microscopically the bacilli are found in all the organs and in the blood. 

 The disease is rapidly communicated from one animal to another, and 

 thus its extension is facilitated. During e'pidemics, rats, mice, and 

 flies, in large numbers, become infected and die, and the disease is 

 frequently transmitted through them to man. The organism is found 

 at times in the feces of sick animals, in the dust of infected houses, 

 and in the soil. 



The virulence of the bacilli in cultures and in nature seems to vary 

 considerably, and rapidly diminishes when grown on artificial media. 

 The growth in cultures becomes more abundant after frequent trans- 

 plantation. The virulence of the organism is increased by successive 

 inoculation in certain animal species, and then its pathogenic properties 

 for other species are less marked. 



Yersin, Calmette, and Borrel have succeeded in immunizing animals 

 against the bacillus of bubonic plague by inoculation, by the intravenous 

 or intraperitoneal injection of dead cultures, or by repeated subcu- 

 taneous inoculation. They also succeeded in immunizing rabbits and 

 horses, so that the serum afforded protection to small animals, after sub- 

 cutaneous injection of virulent cultures, and even cured those which had 

 been inoculated, if administered within twelve hours after injection. 

 The serum has considerable antitoxic as well as bactericidal proper- 

 ties. More recently this serum has been applied to the treatment of 

 bubonic plague in man, with promising results. Experience has shown 

 that the treatment is more efficacious the earlier the stage of the dis- 

 ease. When treatment is begun in the first day of the attack, fever 

 and all alarming symptoms frequently disappear with astonishing 

 rapidity. In cases treated at a later stage larger doses of the serum 

 are required, and even in the favorable cases suppuration of the buboes 

 is not always prevented. In some of the early cases and in many of 



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