ESSENTIALS OF BACTERIOLOGY 



\\ 



Micrococcus Tetragenus (Koch; Gaffky). Origin. 

 Koch found this microbe in the cavity of a tuberculous lung. 

 Gaffky, in 1883, studied its pathogenic actions and gave it 

 the name it now bears. 



Form. Cocci which are gathered in the 

 tissues in groups of four, forming a square 

 a tetrad. (See Fig. 80.) In artificial 

 culture sometimes found in pairs. A cap- 

 sule of light, gelatinous consistence sur- 

 rounds each tetrad. 



Properties. They are immobile; do not 

 liquefy gelatin. 



Growth. They grow well on all nutrient 

 media at ordinary temperature; are facul- 

 tative aerobic. They grow slowly. 



Colonies in gelatin plates. In two days, 

 little white spots, which, when on the 

 surface, form little elevations of a porce- 

 lain-like appearance; under low power 

 they are seen very finely granulated. 



Stab-culture. Small, round, separated 

 colonies along the needle-track, and on 

 the surface a button-like elevation a 

 form of "nail culture." (See Fig. 81.) 



Potato. A thick, slimy layer which can 

 be loosened in long shreds. 



Staining. Colored with the ordinary 

 anilin stains. Gram positive. 



Pathogenesis. White mice and guinea- 

 pigs die in a few days of septicemia 

 when injected with the tetragenus cul- 

 tures, and the micrococcus is then found 

 in large numbers in the blood and viscera. Field-mice are 

 immune. 



In the cavities of tuberculous lungs, in the sputum of 

 phthisical and healthy patients, it is often found, but what 

 action it has upon man has not yet been determined. 



Fig. 81. Stab- 

 culture. Micrococ- 

 cus tetragenus. 



