584 PATHOGENIC BACTERIA. 



a high power exhibit individual movement. The edges 

 of the colony have a fringed appearance, much like the 

 hay or potato bacillus. 



In gelatin tube-cultures the characteristic growth can- 

 not be observed in a puncture, because of the air which 

 remains in the path of the wire. The best preparation 

 is made by heating the gelatin to expel the air it may 

 contain, inoculating while still liquid, then replacing the 

 air by hydrogen, and sealing the tube. In such a tube 

 the bacilli develop near the bottom. The appearance of 

 the growth is highly typical, as globular circumscribed 

 areas of cloudy liquefaction result (Fig. 136), and may con- 

 tain a small amount of gas. In gelatin to which a little 

 grape-sugar has been added the gas-production is marked. 

 The gas is partly inflammable, partly C0 2 . A distinct 

 odor accompanies the gas-production, and is especially 

 noticeable in agar-agar cultures. 



