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Media containing lactose with litmus as an indicator for acidity have been extensively used for growing the colon bacillus and differentiating it from closely allied organisms. This type of medium is well exemplified in Wurtz's lactose litmus-agar which consists of a 1 percent. lactose-agar colored with litmus. These media have several defects, chiefly due to the rapid diffusion of the acid, causing a general reddening of the adjacent medium. This necessitates having plates with few colonies and examining and counting while the colonies are still small. Also gas formation often occurs, ruining the plate.
To overcome these disadvantages, media consisting of stiffer agar have been devised, on which surface smears are made. This is the type of the Conradi-Drigalski medium, which consists of a special nutrient 3 per cent. agar, to which crystal violet is added as an inhibitor for less resistant organisms than the typhoid bacillus.
With the intention
BENDICK AJ. THE USE OF CALCIUM CARBONATE IN SOLID MEDIA FOR THE DIFFERENTIATION OF SUGAR-FERMENTING BACTERIA: ESPECIALLY OF THE COLON-TYPHOID GROUP. JAMA. 1911;LVII(17):1343–1345. doi:10.1001/jama.1911.04260100169003
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