474 BACTERIOLOGY. 
Growth on Gelatin. On gelatin plates small, white 
colonies are developed in from twenty-four to forty- 
eight hours, which, when examined under a low- 
power lens, are seen to be spherical or lemon-shaped, 
grayish-yellow disks, with a finely granular or mul- 
berry-like surface, and a uniform, but somewhat roughly 
dentated border. When the colonies push forward to 
the surface of the gelatin they form white, elevated, 
drop-like masses, having a diameter of 1 to2 mm. In 
gelatin stick cultures the colonies may be either isolated 
or confluent, in the case forming a thick, white, slimy 
mass, filling out the fissures and hollow spaces all 
along the line of puncture; on the surface a broad, 
thick layer of 4 to 5 mm. in extent is apparent. The 
gelatin is not liquefied. 
Growth on Agar and Blood-serum. On plate and 
slant cultures of agar and blood-serum the surface 
of the growth is moist and glistening. The colonies 
appear as small, transparent, round points, which have 
a grayish-yellow color and are slightly elevated above 
the surface of the medium. 
Pathogenesis. Subcutaneous injections of a culture 
of this micrococcus in minute quantity is usually fatal 
to white mice. The animals remain apparently well 
for a day or two, then become quiet, until death takes 
place on the third or sixth day. The micrococci are 
found in comparatively small numbers in the blood of 
the vessels and heart, but are more numerous in the 
spleen, lungs, liver, and kidneys. Gray mice are, for 
the most part, immune to infection by the micrococcus 
tetragenus. Guinea-pigs at times show only a local 
reaction after inoculation, and again die from septi- 
cemic infection. When intraperitoneal injections are 
