128 MANUAL OF MICROBIOLOGICAL METHODS 



Method. Put a column of pyrogallic acid, approximately IJ^ in. high, 

 in the bottom of the empty tube. Stand empty vial in this acid. With 

 pipet, fill vial two-thirds full of NaOH solution. Fashion a connecting 

 unit from the rubber stoppers and rubber and glass tubing. Insert one 

 of the stoppers in the tube with the chemicals. Push down cotton plug in 

 culture tube to a level 1 in. above the medium. Insert second stopper in 

 this tube. Tilt tube containing chemicals sufficiently to allow NaOH 

 solution to spill over the acid. 



Advantages. If a supply of chemicals is at hand, it is useful as an emergency system, 

 when the special equipment required by other systems is not available. Disadvantages. 

 Not suitable for large numbers of cultures, or at least, such use would be more time 

 consuming than other methods. 



Plating System Using Strongly Reducing Medium 



The single plating device introduced by Brewer (1942) is an ingenious 

 method which offers a means of plating cultures without added equip- 

 ment. The dish is used with agar containing strong reducing agents and 

 is designed so that at the periphery the top rests on the medium, forming 

 a seal. The remainder of the top is slightly raised, so that a small amount 

 of air is trapped over the surface. The oxygen entrapped is removed by 

 the reducing agents in the medium. 



Brewer Culture Dish^ 



Materials. (1) Brewer anaerobic culture dish; (2) regular petri dish 

 with bottom either 15 or 10 mm deep; (3) infusion agar suitable for 

 anaerobes which contains suitable reducing agents, such as the following: 

 0.2 per cent sodium thioglycollate, 0.1 per cent sodium formaldehyde 

 sulfoxylate, and 0.0002 per cent methylene blue. 



Method. Pour sterilized medium in bottom of regular petri dish (25 ml 

 minimum in 10-mm dish and 40 ml minimum in 15-mm dish). Streak 

 center area from sample or culture. Replace the lid of the regular dish 

 with the Brewer anaerobic lid. (The lid at its periphery should touch the 

 agar at all points in order that a perfect seal be obtained. In the success- 

 fully prepared dish, the agar in the center of the dish remains colorless 

 while the blue color returns to the agar at the end of the dish because of 

 oxygenation of the dye which serves as an oxidation-reduction-potential 

 indicator.) Place plates in the incubator immediately after they are pre- 

 pared, and examine as needed during the incubation period. When trans- 

 fers are to be made from the plate, break the seal by a slight turn of the lid. 



Advantages. A useful, quick method of single-plate culture. An extremely simple 

 method which is easy to learn and use. The only trick in the technic is to have 



1 Brewer anaerobic dish. Baltimore Biological Laboratory, Baltimore, Maryland, 

 and Kimble Glass Company, Vineland, New Jersey. 



