Bacillus Pestis Bubonicae, Yersin, Kitasato (1894). 



BLAdK OB BUBONIC PLAGUE; BLACK DEATH;- PEST. 



Origin. — In the enlarged or suppurating glands or buboes; in 

 sputum in the pneumonic form of the disease. Also present in the 

 urine and feces. In severe cases may be present in small numbers in 

 the blood. 



Form.— A short, thick bacillus with rounded ends {cocco-hacilhtii). 

 At times, may be almost a coccus and may form short chains, of 6-8 

 cells. It is subject to great variation in form, and not infrequently 

 is surrounded by capsules. Involution forms are frequent, especially 

 in the presence of mercury, salt and other antiseptics. 



Motility. — Itis said to be non-motile. May have 1 or 2 flagella 

 (Gordon). Brownian motion is marked. 



Spokulation. — No spores observed. It is a relatively weak organ- 

 ism; a few minutes at 58° kills. 



Anilin dyes.— It stains readily; Gram's method is not applica- 

 ble. At times, a bi-polar stain may be observed and in the case of 

 short threads the resulting appearance is not unlike that of the 

 "beaded" tubercle bacillus. Abnormal forms do not stain well. 



Growth. — Is slow and not abundant. The, cultures die'out readily. 

 They are usually slimy. 



Plates.— The colonies on a^ar are small, transparent and white, with iridescent 

 edges. On gelatin the colonies are very small, circular and sharply bordered; eventually 

 they become brown and coarsely granular. 



Sia6 culture, — Shows a very slight white growth along the line of inoculation, and 

 spreads but little on the surface. At times, minute branches extend into gelatin from the 

 puncture, the resulting appearance resembles somewhat an anthrax stab culture. 



Streak culture, — On a^ar\\. forms a rather thin, whitish, slimy growth which usually 

 is made up of discrete colonies. The old cultures show large coccus-, or tbrula-llke forms, 

 and but very few typical ovals or short rods. Glycerin agar yields a better growth.' It 

 grows well on serum ; poorly on potato. 



Bouillon. — In this the growth is very characteristic and resembles that of the strep- 

 tococci. The liquid usually remains clear while the granular or slightly flocculent, moderate 

 frrowth develops on the walls and bottom of the tube. Old cultures show a ring or " col- 

 aret" on the surface of the liquid. A bouillon with 2 per cent, each of pepton and 

 glycerin furnishes the best medium . On staining, various bizarre forms are met witti. Short 

 threads of £h8-io cells like streptococci are present. . Good rods may be present but the 

 size of the cells varies greatly. 



Milk.— Is not coa§;ulated. Acid is produced in bouillon. An indol reaction results 

 on the addition of a nitrite. 



Oxygen requirements. — It can grow as a facultative anaerobe, 

 but only in gelatin. 



Temperature. — It grows well at the ordinary room temperature. 

 Prolonged exposure to 37° is unfavorable. Cold has no effect. 



Behavior to gelatin. —It does not liquefy. 



Aerogenesis. — Not observed. 



Attenuation. — Takes place readily. Cultures from convalescents 

 may be non-virulent. Other growths rapidly lose their virulence on 

 artificial culture. By successive passage through animals or by the 

 coUodium sac method (Chapter XIV), the virulence may be greatly 

 increased. A culture of maximum virulence obtained by passage 

 through mice is feeble with reference to rabbits, and vice versa. 



Immunity. — Can be obtained by means of agar cultures. The 

 injections, at first, are made with cultures heated at 58° for 1 hour. 

 Subsequently, living cultures are injected intravenously. The rabbit 

 and horse can be thus readily immunized, whereas guinea-pigs are 

 diflacult. The serum of the immunized horse is anti-infectious and to 

 less extent antitoxic As usually tested 0.1 c.c. of the serum should 

 protect a white mouse against 10 mg. of the toxin which has been 

 precipitated by (NH4)2S04. 2.5 mg. of this toxin will kill a control 

 mouse in about 12 hours. Vaccination by repeated injection of bouil- 

 lon cultures, heated to 70° (Haffkine). 



Pathogenesis, Infection and Diagnosis. — See p. 383. 



358 



