Electron Micrographs Made From L Forms of Proteus and Two Human Strains of Pleuropneumonia-Like Organisms,

The organisms in the cultures of the pleuro-pneumonia group and of the L forms of bacteria are visible with the light microscope. Their morphology has remained controversial for a long time because they are easily deformed in micro-scopic preparations and give riise to bizarre forms. It seems well established at present (Klieneberger and Smiles, 1942; Dienes, 1945) that the cultures, with a few exceptions, consist of round forms which vary in size by continuous transition from barely visible ones to those several micra in diameter. The exceptions are the organisms of bovine pleuropneumonia and of agalactia in the cultures of which the small granules grow out into fine branching filaments which later develop swellings or break up into other granules. Accord-ing to Freundt (1952), branching filaments also are present occasionally in the cultures of other pleuropneumonia-like strains. Reproduction oc-curs either by binary fission as in bacteria or by the production of small forms in varying numbers inside the larger ones (Dienes and Weinberger, 1951). The size of the smallest viable element in one bacterial L form, an old Li isolated from Streptobacillus moniliformis (Klieneberger-Nobel, 1949), has been determined by filtration through gradocol membranes. It was found to be at the borderline of visibility between 0.175 and 0.25 I,u about the same as in the pleuropneumonia group. The electron micrographs of these organisms which have been published have added little new information on their morphology (Freundt, 1952; Smith et al. 1948a, b). The fragility of the or-ganisms made it difficult to make preparations appropriate for electron micrography. We had