192 PRACTICAL BACTERIOLOGY. 



with the forceps as quickly as possible, with the 

 colony adhering to it. Such a preparation is called 

 an "impression cover-glass preparation." It should 

 be then put aside for a time to dry. 



In order to observe the different ways in which the 

 anthrax bacillus grows on different media, test-tubes 

 containing gelatine and agar-agar are inoculated 

 with small portions taken from one of the colonies of 

 a plate culture. Its growth on potatoes is not 

 peculiar ; dull, greyish- white masses, generally only a 

 few millimetres in breadth, develop along the track 

 of the needle. On agar-agar a slimy film is formed, 

 in colour of a dirty white, often inclining to red ; after 

 a few days, peculiar bright spots appear, through 

 which the agar-agar can be seen, so that it looks as 

 though bubbles had been formed at these places. 

 The gelatine soon becomes liquefied-; this occurs least 

 rapidly in puncture cultivations and only after another 

 equally characteristic growth has shown itself. At 

 first a thin white thread appears along the track of 

 the needle. This becomes thicker and thicker the 

 nearer it approacbes the surface, whilst it gradually 

 disappears in the' lower layers of the gelatine. A 

 great number of fine tlireads radiate out from the 

 central one, and, as a rule, become branched again. 

 These diminish in number as they descend, so that at 

 the end of the thread there are scarcely any to be 

 seen. On the surface they sometimes extend right 



