SUMMARY:Mimobes were grown on microscope slides so that the growth could readily be observed by phase-contrast microscopy.ProtGUs &garis, grown on agar containing peNcillin, undergoes extraordinary morphological changes which vary with the temperature of incubation, the concentration of the penicillin, the concentxation of the agar and the presence of small amounts of fluid between the agar and the cover-slip. The bacilli may divide noxznally once or twice into elements that grow without dividing and which may develop into fantastically shaped thread or swollen forms. In high concentrations of penicillin the fantastic shapes are obtained by enlargement without division. At first the nuclei divide as in nomud organisms. The thread forms have condensed nuclei arranged in alternating pattern along the side of the cells. In the swellings there may be either nuclear material Wing the cells, a condensed central mass or a reticulum. When vacuoles are present these displace the nuclear material.When the misshapen organisms are transferred to a medium free from penicillin and containing penicillinase they divide, forming normal bacilli. Many of the swollen elements burst and disappear.The motility of the greatly enlarged organisms is sluggish, and flagellar movement can clearly be observed by phase contrast. The movement of the flagella of the organisms responds readily to radiant heat, and a careful study of these movements makes it impossible to accept Pijper's contention that bacterial motility is due entirely to undulatory movements of the body and that the flagella are merely mucoid strands cast off as the result of motility."he flagella were demonstrated in the large forms by fixing the culture through the s g a~ for several days, detaching the agar and stainingthe cover-slip, which carries the fixed colony, with a saturated watery solution of night blue. The nuclei were shown by treating films with hot nitric acid, washing and staining first with cresyl blue then Leishman's stain.

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A numerical classification study was carried out on 129 strains representing "Mycobacterium" rhodochrous, Runyon's Group IV mycobacteria, and other related taxa. Cultures of these strains were examined for 170 characters, and the resultant data have been analyzed by computer. Similarity coefficients were calculated in two ways: by the first, negative and positive matches were scored, and in the second, positive similarities only; in each case. clustering was with the average linkage cluster analysis technique. The two coefficients of association yielded the same four clusters, and, with a single exception, substantially the same subgroups. The three homogeneous clusters corresponded to: (i) "M." rhodochrous, (ii) Nocardia pellegrino, and (iii) Mycobacterium Group IV. Twenty-three named mycobacteria were recovered in seven subgroups, six of which were equated with the established taxa M . borstelense, M. chitae, M. gallinarum, M. fortuitum, M. smegmatis, and M. vaccae. Characters were abstracted from the data and used for the identification of clusters and subgroups.