Abstract
The existence in certain bacterial stock cultures of two types of cells, characterized respectively by the formation on agar plates of (R) and (S) colonies, has been demonstrated for a number of bacterial groups (Shiga bacillus, paratyphoid and typhoid bacilli, Bacterium lepisepticum , pneumococci, hemolytic streptococci, cholera vibrios and Proteus 1 ). Under ordinary conditions, transfers from the S and R colonies breed true. The importance of the two types of colony formation is shown by the correlation of characters: subcultures from smooth colonies form stable suspensions in salt solution, while the cells from rough colonies tend to agglutinate spontaneously. The acid agglutination optimum is higher for the S than for the R type; the S type is more virulent than the R, and there are significant serologic differences. In the examination of more than a hundred strains in my collection of paratyphoid bacilli, 2 there has been in all
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