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READ (1939), employing various methods for the differential isolation of V. cholerae from mixtures of stools and waters inoculated with V. cholerae, found that a modification of the bismuth-sulphite enrichment medium of Wilson & Blair gave the best results and enabled him to isolate the vibrio from an inoculum that would only just grow in ordinary broth. Briefly, the modification consisted in the omission of brilliant green, increase of pH. to 9-2, substitution of mannose for mannitol in 1 % concentration, and replacement of broth by peptone water. The new medium, in addition to the inhibitory effect of the sulphite-bismuth complex on the growth of B. coli and many other saprophytic organisms, possesses the advantage that the sodium sulphite in it tends to keep the pH. at a high level and thus at a point favourable to the development of V. cholerae and unfavourable to many accompanying organisms. As the discoverer of the selective action of bismuth sulphite media and their application to the isolation of proteus, typhoid and paratyphoid bacilli, one of us (W. J. W.) decided to study the subject to see if Read's interesting observation could be confirmed. Whilst we were engaged in this work a paper by Seal (1939) appealed giving the results of a preliminary field trial at Calcutta of Read's modification of the Wilson & Blair medium. Seal found that of the cases of clinical cholera 64-7 % yielded V. cholerae in this medium as compared with 43-1 % in alkaline peptone water and that eight of the 117 tank waters examined yielded positive isolations in the new media, whereas only five of them were positive in alkaline peptone water. Seal also found that compared with alkaline peptone water there was some restriction of growth of the inagglutinable vibrios in the bismuth sulphite mannose medium. The formula of Read which we made the basis of our study was: peptone 2% 8-8 c.c, sea-salt mixture 1*2 c.c, stool emulsion 10 c.c.-, liq. bismuthi 0-12 c.c, sodium sulphite 20% 1-2 c.c, mannose 10% 1 c.c, absolute alcohol 0-2 c.c, HgCLj 1/10,000 0-8 c.c, pR 9-2. These 23-3 c.c. were contained in screw-capped bottles. Having had further experience of the use of sulphites and bismuth since 1931 when the paper of Wilson & Blair to which Read refers was published, we did not follow in every detail our old technique. Besides fluid enrichment media we tested solid media and describe in this paper a medium which might be employed in place of that of Dieudonne & Aronson.

Bismuth sulphite media for the isolation of V. cholerae