AEROBIC SPORE-BEARING NON-PATHOGENIC BACTERIA 291 



Litmus glucose agar colonies. Irregular, spreading, bizarre 

 surface colonies, usually more luxuriant than plain agar colonies. 

 Under low power, irregular with entire edges or fuzzy, with 

 myceleoid outgrowths from dense central nuclei. Deep colonies 

 slightly irregular or punctiform. Under low power irregular 

 myceleoid with filamentous edges. Medium first acidified then 

 made alkaline. 



Gelatin stab. Slow growth along line of inoculation and rather 

 slow cup-shaped, surface liquefaction with scum production. 



Gelatin colonies. Surface colonies round, homogeneous, spread- 

 ing, thin and granular. Deep colonies yellowish brown, highly 

 refractive. Under low power granular. Colonies may also 

 show dense central nuclei and thin myceleoid filamentous growth 

 extending in every direction through the medium. Gelatin 

 liquefied. 



Broth. Single isolated pelHcles appear on the surface in 24 

 hours. In 48 hours these unite to form a thin branching scum, 

 which gradually becomes more dense and tough. Medium 

 grows turbid in first 24 hours, but later clears. Scum is pre- 

 cipitated as a whole in about ten days. This manner of scum 

 formation is characteristic of Bacillus subtilis. 



Peptone. Turbidity in the first 24 hours and gradual clearing 

 with a flocculent precipitate. Scum on the surface formed in 

 the same manner as on broth, but not so dense or tough. The 

 pellicles often show chains and branching figures. Frequently 

 the scum has a delicate pink color after about five days' growth. 



Potato. Growth on potato characteristic. It is luxuriant 

 and warty, having the appearance of many large and small dew 

 drops scattered along the fine of inoculation. In 48 hours a 

 pink pigment collects on top of this growth and persists. In 

 older cultures a decided rose-red fine in the substance of the 

 potato marks the limit of the growth. In ten days the vesicles 

 dry down and only a reddish-brown dry growth remains on the 

 discolored medium. Later the growth is moist and sticky. 



Litmus milk. No change in 24 hours and sometimes none in 

 48 hours except that the milk becomes more alkahne. In three 

 days the medium begins to clear from the surface, the deeper 



