x] BACILLI : SPECIAL 193 



white in reflected, brownish in transmitted light ; on the top 

 of the stab is a translucent, plate-like expansion of the 

 growth. After two, three, or four days' incubation this ex- 

 pansion covers the whole upper surface of the gelatine, 

 while in connection with the stab there are a few large flat 

 gas bubbles hanging on, as it were, to the growth in the stab. 

 The gas bubbles in the upper layers of the shake culture 

 gradually break through and escape on to the free surface, 

 so that after a time only the deeper layers still contain gas 

 bubbles. Neutral litmus-whey is turned red by the growth 

 of bacillus coli (Petruschki). 



On the surface of Agar the growth is a grey, dry film, not 

 possessing any special character. 



On potato it forms a light yellowish-brown expansion. 

 Alkaline broth becomes strongly and uniformly turbid at 

 37" C. already after twenty-four hours ; later, while the 

 turbidity increases, a whitish, floccular, granular precipitate 

 appears in the depth, and on the surface an attempt at the 

 formation of a white, imperfect pellicle. 



If after 3 — 5 days' incubation a few drops of potassium 

 nitrite solution, and then a small quantity of nitric acid, are 

 added to the broth culture, a characteristic pink colouration 

 appears, due to nitroso-indol, the typical bacillus being a 

 strong decomposer of albumen, forming thereby indol. In 

 milk incubated at 37" C. the typical bacillus coli grows 

 copiously, and clots and solidifies the milk already in 

 30 — 48 hours, or latest three days ; after clotting a separation 

 of the clot from the whey takes place. These are the 

 principal morphological and cultural characters of the 

 typical bacillus coli, and it remains to be added that, 

 stained for flagella after van Ermengem's method, the 

 bacilli contain at one or both ends several flagella — two, 

 three, up to eight altogether; the flagella are wavy, whip- 



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