TUBE CULTURES. 73 



on the surface and along the stab. Some species liquefy the 

 gelatin and others do not. Some bacteria liquefy the medium 

 in a manner which is characteristic of the germ. 



Gelatin cultures may also be embedded and sectioned : The 



FIG. 27. 



Series of stab cultures in gelatin, showing modes of growth of different species 



of bacteria. 



tube is warmed a little so as to loosen the gelatin (without 

 melting it), which then is transferred to and fixed in Mueller's 

 fluid. It is hardened in alcohol, embedded in celloidin, sec- 

 tioned, and stained like tissue preparations. Winkler suggests 

 filling a cavity in a block of paraffin with sterile gelatin. 



