Factors affecting the growth ofStreptococcus faecalison glucose-yeast extract-sodium azide agar have been studied. Both the high temperature of incubation used (45° C.) and the presence of azide reduced the proportion of cells able to form colonies, the inhibitory action being much more marked with cultures which had become attenuated, either through age or through prolonged immersion in water, than with comparatively young and vigorous cultures. This inhibitory action was found to be largely overcome if the inoculum was subjected to a preliminary period of ‘resuscitation’, by incubating it with double-strength glucose broth before adding the azide-agar portion of the medium and allowing the mixture to set.Neutral red was so inhibitory to some strains ofStr. faecalisthat it could not be included in the medium. Phosphate, as the potassium salt at a concentration of 0.7%, if autoclaved with the remaining constituents of the medium, exerted a depressing effect on the counts. Added separately it showed no inhibitory action.The spinning-bottle technique (Allenet al.1952) was adapted forStr. faecalis. When used for samples containing a mixed flora the method, described in the Appendix, permitted the growth only ofStr. faecalis.This paper is published by permission of the Department of Scientific and Industrial Research.

SUMMARY: The effect of various conditions on the rate of death of Bacterium coli and of Streptococcus faecalis in dilute buffer solutions was followed by making colony counts at intervals during prolonged periods of incubation and then constructing mortality curves. The form of these curves was characteristic for each organism. Of the pH values investigated (approximately 5, 6, 7 and 8) both organisms were least viable in the range 6 to 7. Strep. faecalis was not affected by the degree of oxygenation of the water but Bad. coli died much more rapidly under anaerobic than under aerobic conditions. Growth of Bact. coli was observed with as little as 0.28 part per million organic matter in solution. A much higher concentration of nutriment was required for growth of Strep. faecalis; with a concentration slightly below that required for growth the viable population remained virtually stable for a long period. The rate of death depended on the age of the cells a t the time of immersion in water.Factors affecting the longevity in water of organisms used as indices of pollution are of importance in the sanitary survey of rivers or in assessing the suitability of water for drinking purposes. Reports in the literature suggest that the period of survival may be conditioned by a number of factors but the conclusions drawn are often open to doubt owing to failure t o arrange for conditions to be the same in comparable experiments. Moreover, in earlier work there is often some doubt of the precise characters of the organism referred to as Bacterium coli. \'ery few observations appear to have been made on the longevity of Streptococcus fa