148 



BACTERIOLOGY. 



then to be held in a horizontal position and twisted 

 between the fingers upon their long axis under ice- 

 water. The gelatin becomes 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 the tubes set aside 

 for observation. 



For some time past we have deviated from the direc- 

 tion given by v. Esmarch for this part of his method, 

 and instead of rolling the tubes under ice-water, we roll 

 them upon a block of ice (Fig. 28), after the method 



FIG. 28. 



Demonstrating Booker's method of rolling Esmarch tubes on a block of ice. 



devised by Booker in 1887 in the Pathological Labora- 

 tory of the Johns Hopkins University. In this method 

 a small block of ice only is needed. It is levelled 

 and held in position by being placed upon a towel in 

 a dish. A horizontal groove is melted in the upper 

 surface of the ice with a test-tube of hot water. The 

 tubes to be rolled are then held in an almost not quite 



