Journal of bacteriology . (CultureBi) Fig. 2. Same as figure 1 except a different strain of B. lactis-acidi was used. for the quantitative bacterial analysis of milk, and since glu-cose is cheaper it should, perhaps, be recommended as the stand-ard for routine work. A limited number of trials have also * Jour. Infect. Dis., 5: 412-420. ADVANTAGES OF A CARBOHYDEATE MEDIUM 487 indicated that the amount of carbohydrate may be reduced per cent without impairing the value of the medium. Another advantage of a medium containing a carbohydrateover plain agar is that the former is of considerabl
Journal of bacteriology . (CultureBi) Fig. 2. Same as figure 1 except a different strain of B. lactis-acidi was used. for the quantitative bacterial analysis of milk, and since glu-cose is cheaper it should, perhaps, be recommended as the stand-ard for routine work. A limited number of trials have also * Jour. Infect. Dis., 5: 412-420. ADVANTAGES OF A CARBOHYDEATE MEDIUM 487 indicated that the amount of carbohydrate may be reduced per cent without impairing the value of the medium. Another advantage of a medium containing a carbohydrateover plain agar is that the former is of considerable value indifferentiating the types of organisms on the plates. The colo-nies of acid-producing bacteria on sugar agar are surrounded by. ^1 YepiOCOCCU5 Fig. 3. Same as figure 1 except a culture of a streptococcus was used. a precipitate of protein matter, thus giving the typical hazyedge which is so characteristic of organisms of the B. lactis-acidi group. On agar made without clarification with egg albu-men, and which is consequently more opaque, the peptonizingbacteria may be quite readily identified by means of the clear 488 JAMES M. SHERMAN halo which surrounds their colonies. This differentiation ismuch clearer on plates containing lactose or glucose agar than onthose with plain agar, as the opacity of the medium is very muchincreased in the presence of a fermentable carbohydrate, due tothe growth of acid-producing organisms. In fact, unclarifiedlactose agar gives, in our hands, nearly as clear a differentiationof bacterial types as does the special casein agar devised byAyers.^ These points are well illustrated by the followingphotographs. SUMMARY Data are presented which it is thought warrant the recommen-dation
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