630 



PATHOGENIC MICROORGANISMS 



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 



1 2 3 



FIG. 66. BACCILLUS COLT COMMUNIS, Grown in: 1. Dextrose, 2. Lactose, 

 3. Saccharose broth. The baccillus forms acid and gas from dextrose and lactose, 

 not from saccharose. Note the absence of growth in the closed arm of the sac- 

 charose tube, in which no acid or gas is formed. 



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 

 coagulation. 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, pis is formed in dextrose, lactose, and mannit, 

 but not in saccharose. Levulose, pilactose, and maltose arc also fer- 

 mented with the formation of acid and gas. ' 



