474 BA GTERIOL OGY. 



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 to 2 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- 

 csemic infection. When intraperitoneal injections are 



