STREPTOCOCCI. 383 



DIAGNOSIS. The organism may be found, at times, in the blood of 

 yellow fever patients. 2 c.c. of blood should be drawn (Chapter XIV), 

 added to liquefied agar or gelatin 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 g-elatin and on ag-ar. 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 mice or rats in 1-3 days: to 

 guinea-pig's in 2-5 days; to rabbits in 2-7 days; to monkeys in 2|-5 

 days. The horse, pig-eon, 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 -inocu- 

 lation form; or by inhalation p?ieimiomc 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 



