The Kinds of Bacteria found in River Water

Abstract

1. The kinds of bacteria that are isolated by the gelatin plate method from certain river waters freshly polluted with sewage are different from those found in the same water collected a long distance below the point of pollution.2. In the freshly polluted river water non-chromogenic Staphylococci were found much more abundantly than in the purer waters.3. In the freshly polluted water the fluorescent bacteria and a group of non-gas-producing, non-liquefying bacteria (Group XI.) were less abundant than in the purer waters.4. A larger proportion of organisms belonging to the Proteus group were isolated from gelatin plates than from fermentation tubes. The reverse is true of the B. coli and B. lactis aerogenes types. A certain selective influence even upon gas-producing organisms would seem from this to be exerted by the conditions within the fermentation tube.5. The study of a rather large number of separately isolated cultures belonging to the class of fluorescent microorganisms shows that the differences between the ‘liquefying’ and ‘non-liquefying’ varieties are more constant than is sometimes assumed. The action of these forms upon milk is just as diagnostic as their action upon gelatin. All the strains of fluorescent bacteria that were encountered (58) proved to be motile.6. Considering as a whole the various physiological tests applied to the several groups of microorganisms, it is found that within almost every group as constituted in the accompanying tables divergence is shown by closely allied organisms in respect to indol formation and reduction of nitrates. The formation of a surface pellicle on broth is also a phenomenon that presents no apparent correlation with more s alient physiological characteristics.