518 BACTERIOLOGY. 



eter, grayish- white in color, viscid and non-confluent 

 unless very close together. On Loffler's blood-serum 

 the growth forms round, whitish, shining viscid-look- 

 ing colonies, with smooth and sharply-defined outlines, 

 and may attain diameters of one-eighth to one-sixteenth 

 of an inch in twenty-four hours. The colonies tend to 

 become confluent and do not liquefy the serum. In 

 acute cases, where the organisms are apt to be more 

 abundant, a great many minute colonies may develop 

 instead of a few larger ones. On agar plates the 

 deep-lying colonies are almost invisible to the naked 

 eye; somewhat magnified they appear as finely granular 

 colonies, with a dentated border. On the surface they 

 are larger, appearing as pale disks, almost transparent 

 at the edges, but more compact toward the centres, 

 which are yellowish -gray in color. Cultivated in arti- 

 ficial media it soon loses its vitality within six days 

 and requires, therefore, to be transplanted to fresh 

 material at short intervals at least every two days. 



Pathogenesis. This organism does not show much 

 pathogenic power for animals. It is most pathogenic 

 for mice and guinea-pigs, less so for rabbits and dogs. 

 Subcutaneous injections in animals give negative re- 

 sults; intrapleural or intraperitoneal inoculations in 

 mice and guinea-pigs, when given in large doses, are 

 usually successful. Intravenous injections in rabbits 

 have caused the death of the animal, but no diplococci 

 or pathological changes have been found as a result of 

 the injections. 



When mice are inoculated into the pleural or peri- 

 toneal cavities they usually fall sick and die within 

 thirty-six to forty-eight hours, showing slight fibrino- 

 purulent exudation. In the blood and enlarged spleen 



