When the "normal" MS form of hog cholera bacillus was grown for 3 weeks in broth and subsequently plated in semi-solid media, 2 variant forms appeared, a motile rough (MR) form and a nonmotile smooth (NS) form. The NS form subsequently gave rise to a third variant, namely, the nonmotile rough (NR) form.
It is evident from the observations reported that in the case of the hog cholera bacillus the simple S and R conception of microbic dissociation is inadequate to account for the several variant forms. It appears necessary to combine the S and R with the H and O or the flagellar and somatic antigen conception to account for the phenomenon.
The dissociation is represented by the following diagram:
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