CULTURAL CHARACTERISTICS. 39 



away with and the preparation keeps for hours. This is a convenient 

 method for agglutination tests. 



Liquefaction of gelatin is a very important means of differentia- 

 ting. When a room-temperature incubator is not at hand (20 to 22 C.), 

 it is better to put the inoculated gelatin-tube in the body-temperature 



FIG. 10. Series of stab cultures in gelatine, showing modes of growth of 

 different species of bacteria. (Abbott.) 



incubator, and from day to day test the power of solidifying with ice- 

 water. If the organism digests the gelatin (a liquefier), the medium 

 will remain fluid when placed in ice-water if the organism is a non- 

 liquefier, the medium in the tube becomes solid. Of course we lose the 

 information to be obtained from the shape of the area of liquefaction. 



