74 MORPHOLOGY OF THE BACTERIA. 
upon cooked potato, and cultivated by Cohn in 
nutritious solutions. This coloring matter is 
reddened by acids, and restored to blue by al- 
kalies, just as that which forms when lichens 
are macerated in presence of ammonia. 
M. violaceus, Cohn ( Bacteridium violaceum, Schree- 
ter). 
Violet-blue masses or glairy stains formed of 
elliptical corpuscles larger than those of MV. pro- 
digiosus, observed first by Dr. Schneider, then 
by Schroeter on cooked potato. 
Later, Cohn has described the two following 
new species (1876), which should be included in 
this group : 
M. Candidus, Cohn. 
Stains and points white as snow, observed 
upon slices of cooked potato. 
M. fulvus, Cohn. 
Little rust-colored drops, consisting of cells, 
globular or united in pairs, in a tenacious inter- 
cellular substance, diameter 1.5 u, observed by 
Eidam, then by Kirchner, upon horse dung. 
It is also to the genus Micrococcus that we 
must refer the little globular bacteria, gifted 
with movement, found by Eberth in white, yel- 
low, and red perspiration, and by Chalvet in the 
pus on the edges of certain wounds, but which 
should not be confounded with the blue color 
produced by a Bacterium. 
