The Significance ofBact. aerogenesin Water

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Abstract
1.Bact. aerogenesis practically universally present, although in small numbers in the stools of normal adult humans. The stools of one individual, however, repeatedly gave negative results. The organism has also been isolated from the faeces of horse, cow, sheep, pig, dog, cat, wild rabbit, wild rat and wild mouse.2. The use of modifications of the citrate medium, containing lithium or barium, is useful in the isolation ofBact. aerogeneswhenB. pyocyaneusis abundant.3.Bact. aerogenespredominates overB. coliin soil, the contamination of which by faecal material was unlikely. TheB. coliisolated from such soil do not show differences by the tests used from typicalfaecalstrains ofB. coli.4. In the municipal water supply of Liverpool the proportion ofBact. aerogenestoB. coliis relatively high and increases on storage.5. In water contaminated with faeces, the proportion ofBact. aerogenestoB. coliis relatively low but is rapidly reversed on storage. This is largely due to the death of theB. coli, but may in part be also due to multiplication of theBact. aerogenespresent.6. Preponderance ofBact. aerogenesoverB. coliin a water supply is indicative of either (a) contact with soil which is not contaminated with fresh faeces, or (b) long past faecal contamination.7. Preponderance ofBact. aerogenesoverB. coliin a water supply may, for practical purposes, be regarded as an indication of freedom on the part of the water from pathogenic organisms, includingB. typhosusandB. paratyphosusB.8. The repeated examination of faeces during storage showed a marked increase followed by a gradual decrease in the total number of organisms present. The decrease coincided with an increase in the numbers ofBact.aerogenesrelative to the organisms present. Whether an absolute increase in the numbers ofBact. aerogenesoccurred, was not determined.9. A plea is made for uniformity among the tests adopted by future workers for the identification of coliform organisms, and an exact statement of the methods employed.The writer desires to thank Prof. J. M. Beattie for helpful advice throughout the course of the investigation.