In previous papers the isolation and description of numerous variant forms of Micrococcus tetragenus was reported.1 It was at first believed that these interchangeable variants composed a complex system of bacterial variation different from the orderly one associated with other bacteria. A clue to the solution of the problem was provided many months later by the detection of typical rough colonies among the pink colonies already studied. An orderly arrangement of most of the variants and a basis for comparison with other bacteria was then made possible.2With the rough-pink form at hand, this form and the mucoid-pink and pink were grouped together as the usual M, S, and R culture-phases of a given bacterial type. On this basis it was predicted2 that the yellow, white, pink, pink-yellow, and brown forms represented distinct types of M. tetragenus and that each possessed the respective culture-phases. In subsequent investigation involving the aging of 100 cc. broth cultures of the types at hand for months at...