An appreciation of the brucellin skin test.

brandenburg, stanley, and anatum, showed no reduction in viable count compared with MacConkey's medium. The growth of salmonellae was somewhat slower than on ordinary MacConkey agar but most produced colonies of 1 mm diameter at 22 hours and only five required incubation for 36 hours. Six of the 41 Salmonella species tested failed to grow (typhi, paratyphi A and C, cholerasuis, gallinarum and pullorum) but all are rare causes of food poisoning in Britain. All the faecal flora was prevented from growing apart from occasional strains of lactose-fermenters and some paracolons. Inocula of one million organisms of Pseudomonas pyocyanea, E. coli, Proteus mirabilis, vulgaris and morgani, Klebsiella aerogenes, and Shigella sonnei were completely suppressed. The new medium was simple and reproducible from batch to batch. An outbreak of S. enteritidis food poisoning amongst nursing staff allowed a comparison of the results from the new medium with those from deoxycholate-citrate agar (DCA). Each sample of faeces from 640 people was examined in two laboratories, one employing selenite F and the new medium and another making orthodox use of first class DCA and selenite F. The total number of salmonellae isolated from the new medium was 36 compared with only 22 from DCA. The new medium appeared to be a distinct advance on any other for the investigation of salmonella food poisoning.