BACILLUS OF BUBONIC PLAGUE 199 



lymphangitis and enlarged axillary glands. The plague bacilli were found 

 in the secretion from the pustule. Notwithstanding the very alarming 

 initial sickness, recovery took place. In man, the bacilli are most 

 numerous in the enlarged suppurating lymphatics. They are also pre- 

 sent in smaller numbers in the blood and the internal organs. 



Bacteriological Diagnosis of Plague. As already mentioned, 

 the characteristic bacilli are very numerous in the pustules or buboes, 

 and the polar staining exhibited with methylene blue enables them to 

 be easily differentiated. The bacillus of chicken cholera resembles it, 

 but is somewhat larger, and has no effect on man. The diagnosis is not 

 so easy in those cases where suppuration has not commenced, and it is 

 in such cases that it is most necessary. The German Commission con- 

 sider puncture of the bubo somewhat dangerous, on account of opening 

 bloodvessels, but the English doctors make a long incision in the 

 affected gland, which is afterwards dressed with antiseptics. By this 

 method it is easy to obtain material from the gland for cover-glass 

 specimens, plate, and other culture methods. Microscopical examina- 

 tion of the blood is only attended with results in cases of general 

 infection. Culture experiments with the blood yield better results. To 

 separate plague bacilli from the mixture of bacteria in sputum, it is best 

 to make gelatine stroke plate cultures. The suspected material is drawn 

 across the surface of solid gelatine, several strokes being made. The 

 plague bacilli grow very well at the low temperature of 22 to 25 C., 

 while the accompanying bacteria, i.e., diplococcus lanceolatus streptococ- 

 cus, generally exhibit only a scanty growth. According to Hankin, when 

 the bacilli are grown on agar containing 2' 5 to 3" 5 of salt at 31 C., in 

 twenty-four to forty-eight hours involution forms, consisting of pear- 

 shaped bodies and spheres, appear, which he considers characteristic 

 enough to form a means of diagnosis. Of further diagnostic importance 

 is the fact that the blood serum of men and animals recovered from 

 plague possesses the power of agglutination (German Commission). This 

 power of agglutination appears first in the second week, and in the 

 second and third it is mentioned as being most pronounced. In the 

 cases of mixed infection, particularly those accompanied with suppura- 

 tion of the buboes, streptococci are found not only in the glands, but 

 also in the blood. 



Immunity. In the Pasteur Institute a plague serum is prepared 

 from a highly immunized horse. The German Commission, experi- 

 menting with this serum, found that 3 c.c. was sufficient to protect a 

 brown monkey against an after subcutaneous inoculation. With the 

 susceptible grey monkey 10 c.c. was not sufficient. The serum also 

 exhibited undoubted curative effects on a brown monkey inoculated 

 twelve hours previously. Haffkine prepares his anti-plague serum 



