THE ANTHRAX BACILLUS. 193 



up to tbe sides of the test-tube. At the same time 

 the gelatine in the neighbourhood of the puncture 

 liquefies^ the liquid gelatine gradually spreading 

 downwards and also superficially, until the sides of 

 the test-tube are reached. After ten days, as a rule, 

 the layer of liquid gelatine is about two or three 

 centimetres in depth, and the characteristic appear- 

 ance of the puncture- culture has disappeared, for the 

 colonies now look like a whitish flocculent precipitate 

 resting upon that portion of the gelatine which is still 

 solid. Generally, growth is arrested by this time, for 

 the layer of liquid gelatine prevents the bacilli from 

 obtaining the oxygen which is absolutely necessary 

 for their development. As a rule, the liquefaction of 

 the gelatine is also ari-ested ; only in very rare cases 

 does it proceed any farther, and then only very 

 slowly. 



The anthrax bacillus also forms spores. In order 

 to observe this process more closely, it is best to make 

 a cover-glass cultivation in the hanging drop. A 

 cover-glass and an excavated slide are sterilised in the 

 usual fashion, and upon the former a drop of sterilised 

 nutrient agar-agar is placed. When this has solidi- 

 fied, a small portion of a plate cultivation colony is 

 transferred to it with the platinum needle. The 

 cover-glass is then reversed, and placed over the slide 

 with the drop hanging down ; the whole affair is then 

 closed up with a drop of paraffin oil, and placed in an 



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