THE ISOLATION AND ESTIMATION OF CLOSTRIDIUM WELCHII

For some time we have been using a technic for the isolation and identification of anaerobic bacteria in feces, believing that we were able to recover all species of the genus Clostridium. All those isolated were identified by means of Hall's key (1922) and confirmed by the best criteria at our disposal. However, after about 100 specimens had been examined, we realized that no putrefactive anaerobes were being recovered. Investigation showed that all the anaerobes isolated were C. Welchii or or-ganisms which differed from it in a few minor respects. The latter were probably atypical C. Welchii. Realizing the importance of this finding, we set out to investi-gate the problem more thoroughly. The method for securing aerobiosis (phosphorus) was not unusual and as human blood agar was the medium used, we were at a loss to explain the phenomenon. A resume of the events which had led to our selection of the method may be of interest. We had set out to find a plate-count method for the study of anaerobes in feces. We thought that, if this were successfully accomplished, we could enumerate and separate the anaerobic species. We felt that the usual method of inoculating given amounts of a bacterial suspension into egg-meat or milk media had several disadvantages. In the first place, it is necessary to heat the suspension to 80°C. for fifteen minutes to kill non-sporulating bacteria. This also destroys the vegetative forms of anaerobes and in species which sporulate poorly (nearly all non-putrefactive strains) most, if not all, the anaerobes would be lost. Second, pure cultures are recovere