ESM 'ARCH'S TUBES. 117 



the ice and rolled, neither rubber cap nor cutting off of 

 the cotton plug being necessary. 



FIG. 26. 



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



The advantages of this process over that followed by 

 v. Esmarch are that it requires less time, is cleaner, no 

 rubber caps are needed, the rolled tubes are more regu- 

 lar, and the gelatin does not touch the cotton plug, as 

 is always the case in the tubes rolled under water, be- 

 cause of the impossibility of holding them steady at one 

 level. 



There is an impression that Esmarch tubes are not 

 a success when made from ordinary nutrient agar-agar 

 because of the tendency of this medium to collapse and 

 fall into the bottom of the tube. This slipping down 

 of the agar-agar is due to the water that is squeezed 

 from it during solidification getting between the medium 

 and the walls of the tube. This can easily be overcome 

 by allowing the rolled tubes to remain in nearly a hori- 

 zontal position, the cotton end of the tube about 1.5 to 

 2 cm. higher than the bottom of the tube, for twenty- 



6* 



