THE MICROCOCCUS TETRAGENUS 633 



aureus, etc.) but Boldoni has shown that the characteristics of these varieties are 

 not stable. Pigment formation is not at all constant. 



An apparently saprophytic micrococcus can be made virulent by growing it in a 

 collodion sac in the peritoneal cavity of a guinea-pig. 



Cultures sterilized by filtration or by heating at 60 C. are very feebly 

 toxic and are not pyogenic. 



SECTION IV. DETECTION, ISOLATION AND IDENTIFICATION OF 



THE ORGANISM. 



On microscopical examination the organism will be recognized by its 

 characteristic appearance. Isolation is easy on gelatin plates the medium 

 is not liquefied. The micrococcus is differentiated from the staphylococci 

 by the fact that it does not coagulate milk [ some staphylococci however 

 do not clot milk (p. 620).] 



FIG. 299. Micrococcus tetragenus. Section of a mouse's kidney, x 1200. 



In those cases in which the strain is virulent the identification of the organism 

 may be completed by the inoculation of a mouse ; in this animal the organism 

 will give rise to a condition of septicaemia and the encapsulated micrococci 

 will be found in large numbers in the blood, internal organs, etc. 



