Abstract
Granular sedimenting growth in liquid medium is one of the principal characters differentiating microbe G (bacillus of rabbit septicemia) from its parent D form. Type G exhibits the granular appearance not only in plain broth, but in serum broth and in undiluted serum as well. This fact led to the examination of the comparative acid flocculation points of the two types. The method used was that of Michaelis, later described in full by Beniasch.
The suspensions of types G and D were prepared by washing the sediments from 5 per cent. serum broth cultures in large volumes of distilled water. After this procedure had been repeated four times, the final suspensions were carefully brought to equal turbidity. Prepared in this way, the G type suspension shows a stability equal to that of D.
The tests for acid agglutinability were carried out with mixtures of Na lactate-lactic acid, range PH = 4.7 to PH = 2.4, and with Na acetate-acetic acid, range PH = 5.6 to PH = 3.2. The mixtures of these buffer series with the microbic suspensions were incubated at 43°C. for 16 hours. Readings were taken at the end of this time. A distinct difference in acid agglutination optimum for the two types was observed. The optimum for type G in general occurs at a range between PH = 4.7 and PH = 4.0. Type D, on the other hand, shows complete sedimentation between PH = 3.5 and PH = 3.0. Many strains of the two types have been examined with invariably the same result. This observation furnishes an important differential criterion for the two varieties. The constancy of the acid agglutination optimum for type D is very strict. That for type G is slightly less so, but the variation is never so great as to cause it to be confused with D.
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