STREPTOCOCCI. 383 



Dia(;nosis. — The organism may be found, at times, in the blood of 

 j-ellow fever patients. 2 c.c. of blood should be drawn (Chapter XIV), 

 added to liquefied agar or g-elatin and plated. It may also be streaked 

 over the surface of inclined agar. Suspected colonies should be re- 

 plated, under conditions of temperature, already emphasized, in 

 order to obtain typical growths on gelatin and on agar. In the ab- 

 sence of characteristic growth the other cultural and morphological 

 properties should be tested. 



Black Plague (p. 358). 



PATHOGENESIS!— It is fatal to white niice or rats in 1-3 days: to 

 -guinea-pigs in 2-5 days; to rabbits in 2-7 days; to monkeys in 2i-5 

 •days. The horse, pigeon, field mouse, hog, cat and frogs are some- 

 what refractory. Doves, chickens, geese, dogs and cattle are said to 

 be immune. Abscesses are frequently produced by the bacillus or by its 

 toxin. On post-mortem the animals show an extensive rose-colored 

 edema, enlarged lymphatic vessels and glands and hemorrhagic con- 

 dition of the abdominal walls. The minute rods are numerous in the 

 blood and internal organs — septicemia. They may be englobulated in 

 leucocytes. Accidental inoculation with pure cultures has proven 

 fatal to man. 



Infection. — The disease naturally attacks mice, rats, hogs, buf- 

 faloes, flies and man. Rats and flies are important as a means of 

 ^spreading the disease. It may be contracted through wounds —inoevr 

 lationform; or by inhalation — pneumonic form; or through the food — 

 intestinal form. 



Diagnosis. — The pus from the bubo will show enormous numbers 

 of the short, oval rods. In the pneumonic form they can be detected 

 ■ in the sputum. The cultural and/ morphological characteristics will 

 be necessary to complete the identification. The involution forms, 

 according to Hankin, are especially marked when the pure culture 

 of the organism is planted on agar to which about 3 per cent, of salt 

 has been added. In 24-48 hours at 37° large spherical or pear-shaped 

 involutions can be found. Pest serum causes agglutination. 



Streptococci (p. 364). 



Immunity. — Can be established in horses and other animals by re- 

 peated injection of filtered or of virulent cultures. The blood-serum in 

 that case is not protective against all varieties of streptococci. This 



