The use of anaerobic jars for the enrichment, isolation and enumeration of anaerobic organisms, though very convenient for larger laboratories, is cumbersome and expensive for smaller ones. We have therefore examined a number of methods that do not require anaerobic jars, and give details of one which we have found satisfactory. Preliminary experimentsMethods involving the use of pumps were considered to be as inconvenient as jar methods. The technique of Fortner (1929, 1957) using Serratiu marcescens as the aerobe is rather uneconomical, and as growth of anaerobes is sometimes slow and not very luxuriant, strict anaerobes may be overgrown by facultative anaerobes. Absorption of oxygen with solutions of pyrogallol and sodium carbonate or copper-spotted steel wool (Parker, 1955) failed to reduce the oxygen tension sufficiently to give rapid anaerobic growth, no doubt because the oxygen-absorbers had become partly saturated before use. We therefore developed a method, originally suggested by Koch (1934) and recommended by Terpstra and Akkermans (1955), involving the use of a dry mixture of pyrogallol, potassium carbonate and diatomaceous earth in double plates sealed with paraffin wax. This mixture does not absorb much oxygen until it is adequately moistened by water evaporated from the medium. Materials and methodsStrains. We used Clostridiunz bifermentwns (1 strain), CE. botulinum (3), Cl. butyricum (4), Cl. welchii (4), Cl. sporogenes ( 7 ) , Cl. pasteurianum ( l ) , a stenothermophilic sulphite-reducing clostridmm isolated from a spoiled meat pack, one strain each of Cl. chauvai, GI. histolyticum, Cl. adenlatiens, Cl. septicum and Cl. tetani, and fiwe strains of Rijidibacte~ium bijidum isolated from infant or adult human faxes.The oxygen-absorbent was a freshly prepared mixture of pyrogallol, 3 g., K,CO,, 3 g. and diatomaceous earth, 15 g., packed in 2 g. quantities in filter-paper envelopes 7 x 4 cm. These were found to reduce the Eh in Koch plates in 3 hr a t 37" C. or in 4 hr a t 32" C. to the level a t which resazurin incorporated in thioglycollate agar is reduced, i.e. to -0.04 volt a t p H 7 . Reagent.Media. The following media were used : Thioglycollate-resazurin broth (Pittman, 1946) plus 1.5 per cent. agar, with or without 10 per cent. by volume defibrinated shecp blood ; sulphite-iron agar (Mossel et al., 1956), containing only 0.05 per cent. sulphite, since we have confirmed Beerens' (1958) observation that some strains of Cl. sporogenes will not tolerate 0.1 per cent. sulphite.For general subculture work thioglycollate-resazurin agar was preferrcd, since failure of the normal colour change from pink to greenish yellow to develop within 3 hr was good evidence that the plate was leaking.Unfortunately resazurin cannot be used as indicator for snlphite-agal* (equilibrium Eh -0.03 at pH 7) or for blood-agar. If these media are used,
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