1 1 6 BACTiERlOLOGY 



In 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 apparatus. Ihe 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 now displaced the original 

 glass plate. 



Streak Method of Isolating Bacteria. — The isolation of bac- 

 teria may sometimes be effected by drawing a platinum wire 

 containing material to be examined 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- 

 izing, over the surface of another, perhaps over several in succes- 

 sion. This method is ordinarily less reliable than the regular 

 plating method. 



Veillon's Tall-tube Method. — Three to six tubes of glucose 

 agar, the agar being at least 6 cm. deep, are liquefied and cooled 

 to 45" C. in a water-bath. A small amount of the material to 

 be examined is placed in the first tube by means of the platinum 

 loop, and carefully mixed. From this dilutions are made in series 

 to tubes 2, 3, 4, 5 and 6, each being carefully mixed without intro- 

 ducing air bubbles. The tubes are quickly solidified by immersion 

 in cold water, and are incubated at 37° C. These culture tubes 

 offer the contained bacteria a wide range of oxygen supply. This 

 is abundant at and near the top, and gradually diminishes lower in 

 the tube until near the bottom almost perfect anaerobic conditions 

 obtain. The method is very useful in isolating B. bifidus from 

 feces of infants, B. acne from acne pustules, and in studying the 

 oxygen requirements of other bacteria and has been most exten- 

 sively employed for study of the bacteria in war wounds, where it 

 has proved to be of fundamental importance. Colonies are picked 

 out with sterile glass capillaries, and deeper colonies are reached 

 by breaking the tube. The successful use of the method requires 

 some practice and particular care, both in the preparation of 



