GENUS MICROCOCCUS 209 



and often a bronze color as the colony grows older. The in- 

 tensity of the color differs considerably in various races of 

 micrococci. Usually shallow, saucer-shaped depressions 

 are formed about the colonies after forty- eight hours or 

 more due to liquefaction of the gelatin. The zones of liquefied 

 gelatin grow larger as the colonies develop until finally the 

 gelatin is all liquefied. The colonies are round and rise from 

 the surface of the medium like a segment of a sphere. In 

 gelatin stab cultures in tubes, liquefaction leads to the forma- 

 tion of a funnel shaped depression, with final complete lique- 

 faction of the medium and sedimentation of the bacteria. 



Potato. On potato, growth is abundant, rather dry and 

 usually deeply pigmented. 



Blood serum. Upon coagulated animal sera, rapid growth 

 takes place and eventually slight liquefaction of the medium 

 in said to occur. 



Bouillon. In bouillon growth is rapid, leading to a gen- 

 eral, even clouding of the medium, and giving rise, after 48 

 or more hours, to the formation of a thin surface pellicle. As 

 growth increases, the bacteria sink to the bottom, forming a 

 heavy, mucoid sediment. The odor of old cultures is often 

 peculiarly acrid, not unlike weak butyric acid.' In bouillon 

 containing sugars, dextrose, lactose or saccharose lactic, 

 butyric, and formic acids are produced. There is no gas for- 

 mation. In proteid media free from sugars, it produces an 

 alkali. 



Milk. In milk, it causes coagulation usually within three 

 or four days, with the formation of lactic and butyric acids. 



Life conditions and properties. Micrococcus pyogenes 

 is a hardy organism growing readily on ordinary media. It 

 produces a ferment-like body which is spoken of as "gela- 

 tinase" and which can be obtained apart from the organism 

 by the filtration of cultures. 1 It is an extremely thermolabile 

 body. It reduces nitrates and produces indol. Its reducing 



1 Loeb. Centralbl. f. Bakt., Bd. XXXII (1902) p. 776. 



