ESMARCH'S TUBES. 89 



level, and is held in position by being placed in a dish 

 upon cloths. A horizontal groove is melted in the sur- 

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

 to be rolled are then held in an almost, not quite, hori- 

 zontal 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, no rubber cap or cutting off of the 

 cotton plug being necessary. 



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, 

 because of the impossibility of holding them steady at 

 one level. 



There is an impression that Esmarch tubes are riot 

 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 at 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 - 

 four hours after rolling them. During this time the edge 

 of the agar-agar nearest the cotton plug becomes dried 

 and adherent to the walls of the tube, while the water 

 collects at the most dependent point, i.e., the bottom of the 



