Bacteriological, physiological, etc
Neutral red-dimethyldiaminotoluphenazine-discovered by Witt in 1879, was not applied to bacterial dkgnosis until 1898, when it was stated by Rothberger that its presence in bouillon agar afforded a useful means of distinguishing between B. coli and B. t y p h u s . Stokes (J. Infect. Dis., 1904, 1, 341) employed a sugar medium containing neutral red in a, Smith fermentation tube, thus enabling the reduction of the neutral red, the quantity of gas'produced, and the ratio of carbon dioxide to
... rbon dioxide to hydrogen, to be noted; he also recognised the selective value of lactose for the diagnosis of B. coZi. 'The present paper is an attempt to ascertain the nature of the changes produced by the reducing bacteria, and the best diagnostic concentration of the components in the Stokes medium. It was found that a neutral red medium composed of from 3 to 4 per cent. peptone, 0.8 per cent. potassium chloride or sulphate, 0.6 per cent. lactose, and 0.008 per cent. neutral red, with a reaction of + 1 per cent., affords a very sensitive and accurate medium for the speedy detection of fzecal pollution by bacteria. The addition of meat broth increases the sensitiveness of the medium, but is not essential. The Stokes neutral red medium is a convenient and reliable one for the detection of faecal contamination in water, and is more sensitive than lactose bile. The yellow fluorescent compound formed by the action of the bacteria is most probably dimethyldiaminomethylhydrophenazine, a simple reduction product of neutral red. Ammonia does not enter into the formation of the reduction product. . W. M. Clark and H. A. hubs. ( J . Agric. Res., 1917,10, 105-lll.)-Since litmus is liable to undergo reduction, or even destruction, during sterilisation in the presence of milk, the use of dibromo-o-cresol-sulphonphthalein is recommended in estimating the degree of acid or alkaline fermentation in milk cultures. This substance is not affected by sterilisation, may be used in dilute solution, and its cost is not excessive.