34 ELEMENTS OF WATER BACTERIOLOGY. 



tory method of "plating out" is not applicable for field 

 work the Esmarch tube process has often been employed. 

 This consists in introducing into a tube of melted gelatin 

 or agar i c.c. of the water and then rotating the tube until 

 the medium has solidified in a thin layer on the inner wall 

 of the tube. In the writers' opinion, this method is open 

 to several objections and does not give as trustworthy re- 

 sults as the laboratory method, even if the samples have 

 to be several hours in transit between the place of col- 

 lection and the laboratory. 



