BACILLUS COLI COMMUNIS 391 



or round. Surface colonies often show a characteristic grape-leaf 

 structure, or may be round and flat, and show a definitely raised, glisten- 

 ing surface. Upon agar slants, growth occurs in a uniform layer. 



On gelatin the colon bacillus grows rapidly, causing no liquefaction. 

 Surface colonies are apt to show the typical grape-leaf formation. Deep 

 colonies are round, oblong, and glistening. In gelatin stabs growth takes 

 place along the entire line of inoculation, spreading in a thin layer over 

 the surface of the medium. 



On potato, growth is abundant and easily visible within eighteen 

 to twenty-four hours, as a grayish-white, glistening layer which later 

 -turns to a yellowish-brown, and in old cultures often to a dirty green- 

 ish-brown color. 



In pepton solution indol is formed. In milk there is acidity and co- 

 agulation. In lactose-litmus-agar acid is formed, the medium becom- 

 ing red, and gas-bubbles appear along the line of the stab inoculation. 



In carbohydrate broth, gas is formed in dextrose, lactose, and mannit, 

 but not in saccharose. Levulose, galactose, and maltose are also fer- 

 mented with the formation of acid and gas. 



Cultures of the colon bacillus are characterized by a peculiar fetid 

 odor which is not unlike that of diluted feces. The acids formed by the 

 colon bacillus from sugars are chiefly lactic, acetic, and formic acids. 

 The gas it produces consists chiefly of C0 2 and hydrogen. The bacillus 

 grows well on media containing urine and on those containing bile. 

 Upon the latter fact some methods for the isolation of the colon 

 bacillus from water and feces have been based. 



Isolation of the colon bacillus from mixed cultures is most easily 

 accomplished' by plating upon lactose-litmus-agar, the Conradi-Drigal- 

 ski medium, or the Endo medium after preliminary enrichment of the 

 specimen to be tested in bile or malachite-green broth. (In the case 

 of feces such enrichment is superfluous.) 



Distribution. The colon bacillus is a constant inhabitant of the 

 intestinal canal of human beings and animals. It is also found occasion- 

 ally in soil, in air, in water, and in milk and is practically ubiquitous in 

 all neighborhoods which are thickly inhabited. When found in nature 

 its presence is generally taken to be an indication of contamination from 

 human or animal sources. Thus, when found in water or milk, much 

 hygienic importance is attached to it. Recently, Papasotiriu ' and, 

 independently of him, Prescott, 2 have reported finding bacilli apparently 



' Papasotiriu, Arch. f. Hyg., xli. * Prescott, Cent. f. Bakt Fief., xxxiii, 1903. 



