BACILLUS COLI COMMUNIS 439 



of concentric differentiation. The colonies in the depth of 

 the gelatine appear as spherical dots, white in reflected, 

 brownish in transmitted, light. 



Gelatine Streak Cultwe. — After twenty-four hours it is a 

 grayish band, thicker in the line of inoculation, gray, filmy, 

 knobbed or crenated in the marginal part. After forty- 

 eight hours it has spread considerably in breadth ; but has 

 retained the above aspect, except that the middle part is 

 more thickened, and the whole growth appears more white 

 in reflected light. After three or four days the band has 

 spread over the greater part of the surface of the gelatine, 

 but it is still dry, filmy, crenate, and irregular in the 

 marginal part, and the whole part, examined under a glass, 

 appears more or less homogeneous. 



Gelatine Shake Culture. — Copious gas formation after 

 from twenty-four to thirty-six hours. 



Agar-Agar Streak. — Forms a grayish-white moist expan- 

 sion. Grows abundantly, producing a dirty-white, faintly- 

 shining expansion. 



Potatoes. — An abundant soft shining layer is produced of 

 light brownish-yellow colour. The growth upon potatoes 

 differs considerably according to the age of the potatoes. 



Milk. — Benders it acid at 37° C, and coagulates it in 

 from twenty-four to forty-eight hours. 



Broth. — Benders it turbid. After from three to five days' 

 incubation at blood-heat, if a few drops of a dilute solution 

 of potassium nitrite solution and then a little sulphuric 

 acid is added, a pink coloration (indol reaction) is obtained. 



While these are in general the characters of the typical 

 bacillus, such as can be isolated from stools normal and 

 pathological, there occur in various other substances — dust, 

 water, sewage, etc. — bacilli which, examined as regards all 

 the above points, coincide in some, but differ in others. 

 These, owing to their general morphological similarity, 



