IN studying the biology of myxobacteria I have arrived at the conclusion that this group of micro-organisms is much more widely spread in Nature than it is commonly considered. The morphology and systematics of myxobacteria are little known to the wider circle of microbiologists, and their role in the circulation of substances in Nature has not been sufficiently studied. In 1933 I discovered cellulose-decomposing myxobacteria of the genus Sorangium, and it was later established that the chief agents of cellulose decomposition under aerobic conditions belong to the family Myxococcacae or Sorangiaceae. This circumstance induced me to turn my attention to different micro-organisms already described in the special literature as causative agents of various transformations of carbon and nitrogen and showing some similarity to myxobacteria in their structure and history of development. The new nitrifying bacteria, discovered in soil by Romell and later by Winogradsky and Winogradskaia and described by them under the name of Nitrosocystis, presented particular interest in this respect. The description of these organisms and the photographs accompanying the report seemed to indicate that these authors mentioned were evidently dealing with myxobacteria.