BACILLUS PROTEUS VULGARIS. 473

like the colon bacteria in shape, others are found as very
long filaments, and occasionally sporulina-forms are met
with. True spirilla-forms are never found. All the
forms mentioned may be met with in cultures of the
same organism. The diameter of the bacillus is usually
about 0.6 //, but the length varies from 1.2 p. or less to 4 /JL
or more. No spores are formed. The organisms are
actively motile. The long filaments frequently form loops
and tangles. Flagella are present usually in large num-
ber; upon one of the longer bacilli as many as one hun-
dred have been counted. Involution-forms are frequent
in old cultures. The bacilli stain well by the ordinary
methods. Gram's method is irregular in action, but
usually fails to color the bacteria.

Upon gelatin plates a typical phenomenon is observed
in connection with the development of the colonies, but
for the most advantageous observation the gelatin used
for making the cultures should contain only 5 per cent,
of gelatin instead 10 per cent, as ordinarily used. Kruse1
describes the phenomenon as follows: uat the temperature
of the room rounded, saucer-shaped depressions, with a
whitish central mass surrounded by a lighter zone, are
quickly formed. Under low magnification the center of
the growth is seen to be surrounded by radiations extend-
ing in all directions into the solid gelatin, and made up
of chains of bacilli. Between the radiations and the
granular center motile bacteria are seen in active
motion. Upon the surface the colon}7 extends as a thin
patch, consisting of a layer of bacilli arranged in threads,
sending numerous projections from the periphery. Occa-
sionally filaments are found in the surroundings. Under
certain conditions the wandering of the processes can be
directly observed under the microscope. It depends not
only upon the culture-medium, but, in part, upon the
culture itself. Entire groups of bacilli or single threads,
by gradual extension and circular movement, detach
themselves from the colony and wander about upon the

1 Fliigge's Mikroorganismen.