518 BACTERIOLOGY. 
eter, grayish-white in color, viscid and non-confluent 
unless very close together. On Léffler’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 
