The Classification of the Colon-Aerogenes Group of Bacteria in Relation to their Habitat and its Application to the Sanitary Examination of Water Supplies in the Tropics and in Temperate Climates. A Comparative Study of 2500 Cultures

(1) The ”lactose+ indol+” index as employed in temperate climate is usually an adequate criterion of water purity. (2) Where a positive test does not appear to be substantiated by the sanitary findings, a further differentiation of the organisms isolated becomes necessary. The methyl-red and citrate tests have been found to supply that differentiation in a satisfactory manner. (3) In the Tropics, false positive “lactose-indol” tests are commonly encountered, owing to the presence in large numbers in soil and water of organisms derived from sources other than recently excreted faeces. (4) In the Tropics, the lactose-indol test should always be confirmed by the methyl-red, citrate and saccharose tests or such other reactions or groups of reactions as may be found by a local survey to be applicable. My very grateful thanks are due to Dr P. A. Clearkin, Deputy Director of Laboratory Service, Tanganyika Territory, for his ready advice and constant encouragement; and also to Mr W. Whitley, Analytical Chemist, who performed a chemical analysis of the water samples, and very kindly gave me the benefit of his opinion on them. In addition I have to thank Dr R. R. Scott, Medical Officer of Health, and the Staff of the Health Office, Dar-es-Salaam, who have rendered every facility in the choice and collection of samples. It is a pleasure to be able to record once more my indebtedness to Prof. Bigger, of Trinity College, Dublin, whose fund of valuable suggestions and kindly criticism has been ever at my disposal.