CHAPTER XVI. 
THE COLI-CLOAC.E-PROTEUS GROUP. 
BACILLUS COLL 
Historical.— Bacillus coli was isolated in pure culture from the 
feces of infants, and its important cultural characters determined by 
Escherich in 1886.^ It is very probable, as Escherich suggested,- 
that Emmerich's B. neapolitanus, Brieger's "propionic acid bacillus," 
and Fninkel's bacilli^ are identical with the colon bacillus. 
Morphology.— B. coli is a rod-shaped organism which varies in shape 
from oval organisms resembling cocci, to bacilli of moderate length. 
The organism varies in size from 0.5 to 0.8 micron in diameter and from 
1 to 3 microns in length. The bacilli occur singly and in pairs; in older 
cultures short chains and elongated organisms are frequently observed. 
The ends are distinctly rounded. Motility is variable; many strains 
are non-motile except during the earlier hours of growth. Young cul- 
tures on gelatin are said to exhibit motility even when older growths 
in the same medium are motionless except for Brownian movement. 
Very commonly only a very few organisms in a microscopic field exhibit 
motion, the remainder being without movement. Four to 8 peri- 
trichic flagella are commonly attached to each bacillus; less frequently 
as many as 12 may be demonstrated. The flagella are somewhat 
shorter than those of the typhoid bacillus and they are more difficult 
to stain. B. coli forms no spores. Capsules have been demonstrated 
in certain cultures.^ It stains readily with the ordinary anilin dyes, 
and it is uniformly Gram-negative. 
Isolation and Culture.— The colon bacillus grows readily on the ordi- 
nary media; the superficial colonies on agar plates are clear and color- 
less and attain a diameter of from 2 to 5 mm. after eighteen hours' 
incubation at 37° C. If the surface of the medium is moist the edges 
of the colonies are somewhat irregular in outline; on dry surfaces the 
colonies are round and slightly convex in section. Viewed by trans- 
mitted light the growths are yellowish-brown; by reflected light they 
are colorless. (\)lonies on gelatin develop more slowly and become 
somewhat brownish in color. The medium is not liquefied. Rapid 
development occurs in plain and sugar broths. A heavy, brownish 
spreading growth occurs on the surface of slanted potato. 
' Die Darmbakterien des Sauglings, Stuttgart, 1886, p. 63. 
- Loc. cit., pp, 73, 74. 
■' Deutsch. nied. Wchnschr., 1885, 11, 583, 603. 
^ Theobald Smith and Gladys Bryant: Jour. Exp. Med., 1927, 46, 133. 
