The non-sporulating anaerobic bacteria, although discovered at about the turn of the century, are as little known to most bacteriologists today as they were thirty years ago. The textbooks of bacteriology give little if any discussion of them, so that it becomes a major research problem for the laboratory worker to identify any of these species when encountered. The importance of the non-sporulating anaerobic bacteria in medical bacteriology is controversial. At the Third International Congress for Microbiology in the section on Anaerobes the following statement was made by Thompson (1): "In clinical bacteriology, anaerobes play a minor role. The finding of anaerobes is analogous to the occurrence of red-letter days on the calendar-when they occur they are usually worthy of consideration." With this statement in mind, inquiry was made regarding the incidence of non-sporulating anaerobes in specimens submitted for bacteriological examination in the Department of Surgery at the University of Chicago, Billings Hospital., From July, 1936 to May, 1940, the following results were obtained: