100 



MANUAL OF BACTERIOLOGY. 



gelatin. Agar roll-tubes should be kept in a position a 

 little inclined from the horizontal, with the neck up, for 

 twenty-four hours, so that the agar may stick to the wall 

 of the tube. 



By the plate-method as originally devised by Koch, instead of using 

 Petri dishes, the gelatin was poured upon a sterile plate of glass. This 

 plate of glass was laid on another larger plate of glass, which formed 

 a cover for a dish of ice-water, the whole being provided with a leveling 



FIG. 33. 







Manner of Making Esmarch Roll-tube. 



apparatus. The plate was kept perfectly level until it had solidified, 

 which took place rapidly on the cold surface. The glass plates were 

 placed on little benches enclosed within a sterile chamber. The more 

 convenient Petri dish has displaced the original glass plate to a large 

 extent. 



The isolation of bacteria may sometimes be effected by 

 drawing a platinum wire containing material to be exam- 

 ined rapidly over the surface of a Petri dish containing 

 solid gelatin or agar; or over the surface of the slanted 

 culture-medium in a test-tube; or by drawing it over the 

 surface of the medium in one test-tube, then, without steril- 



