ESMARCH TUBES. 



133 



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 horizontal position and 

 twisted between the fingers until the sides are moistened 

 by the contents to within about 1 cm. of the cotton 

 plug, care being taken that the gelatin does not touch the 

 cotton, otherwise the latter becomes adherent to the 

 sides of the tube and is difficult to remove. The tube 

 is then placed in the groove in the ice and rolled until 

 its contents are solid. 



FIG. 27. 



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



There is an erroneous impression that Esmarch tubes 

 are not a success when made from ordinary nutrient 

 agar-agar because of the tendency of this medium to 

 shrink and slip to the bottom of the tube. This slip- 

 ping down of the agar-agar is due to the water, which is 

 squeezed from it during solidification, getting between 

 the medium and the walls of the tube. This can easily 



