88 



BACTERIOLOGY. 



present a thin cylindrical lining of gelatin or agar-a^ar. 

 upon which the colonies develop. In all other respects 

 the conditions for the growth of the organisms are the 

 same as in flat plates. 



Esmarch directs that after completion of the dilutions 

 the tops of the cotton plugs in the tubes should be cut 

 off flush with the mouth of the test-tube and a rubber 

 cap be placed over this. They are then to be held in 

 the horizontal position and twisted between the fingers 

 upon their long axes under ice-water. The gelatin be- 

 comes solidified thereby and adheres to the sides of the 

 tube. When the gelatin is quite hard the tubes are 

 removed from the water, wiped dry, the rubber caps 

 removed, and they are set aside for observation. 



FIG. 15. 



For some time past we have deviated from the direc- 

 tions given by v. Esmarch for this part of his method. 

 Instead of rolling the tubes under ice-water, we roll 

 them upon a block of Ice (Fig. 15). In this method a 

 small block of ice only is needed. It is arranged nearly 



