124 MANUAL OF MICROBIOLOGICAL METHODS 



oats or other grain (other tissues, particularly chopped Irish potatoes, 

 may be used but are less conveniently stored for occasional use, and in 

 some cases produce objectionable odors which are evident when the jar 

 is opened) ; (6) tap water. 



Method. Place inverted tumbler (if plates are to be used) or other 

 support in bottom of cylinder. Add oats to fill at least one-tenth of the 

 capacity of the cylinder. Add sufficient tap water to moisten the oats. 

 Stack plates or other cultures on support. Add tube of methylene blue 

 solution (see above). Place layer of plasticene, previously softened by 

 placing in incubator, on rim of cylinder. Push plate-glass square firmly 

 against plasticene; using fingers, press the clay against both the square 

 and the cylinder until a satisfactory seal is obtained. Place jar in 

 incubator immediately. (A 40- to 48-hr incubation period is recom- 

 mended.) 



If plate cultures are employed, replace the ordinary petri dish cover 

 with unglazed porcelain (''clay") tops^ to absorb the moisture which 

 collects within the cylinder. If porcelain tops are unavailable, add a 

 petri dish lid containing CaCl2 to absorb the moisture. 



Advantages. The method is inexpensive and employs easily available materials. 

 No special apparatus is required, an advantage in laboratories where anaerobic cul- 

 tures are not usually prepared. It may be used at any incubation temperature with- 

 out danger of explosion. It is particularly suitable in problems requiring large 

 numbers of plate cultures. It is recommended especially for cultural and physiologi- 

 cal studies of strains which have been purified by other methods. Disadvantages. 

 Several hours may be needed for anaerobic conditions to become established, and 

 therefore the method is not suitable when the results are required quickly. It is not 

 recommended for routine clinical use where speed of isolation of pure culture is an 

 important factor. With certain enrichments it is not suitable for purification of 

 species contaminated with aerobic sporeforming bacteria because of the quick growth 

 of these forms. In plate-culture experiments, as in the isolation of new strains, no 

 one plate may be removed from the cylinder for observation until the end of the incu- 

 bation period, for to do so would destroy the anaerobic conditions within the cylinder. 



Use of Aerobe to Absorb Oxygen 



Another biological method for oxygen removal utilizes the growth of 

 an aerobic organism (usually Staphylococcus aureus, Serratia marcesceus, 

 or Saccharomyces cerevisiae). A wide variety of applications of this 

 system have appeared in the literature. The technics suggested^ involve 

 the growth of the aerobic organism in pure culture on a medium separate 

 from that on which the anaerobe is to be cultured. 



^Unglazed porcelain (''clay") tops for petri dishes. The Coors porcelain dish, 

 sold by Arthur H. Thomas Company, has been found to be more uniform in size and 

 quality than others tested, 



2 These are similar to the Fortner method and are recommended in place of it. In 

 the Fortner method the aerobe is streaked on one half of the plate and the anaerobe 

 on the other half of the same dish. 



