SURFACE TENSION AND BACTERIAL GROWTH

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Abstract
The surface tension of broth was determined by the drop-weight and the film methods. The latter gave results 10-12 dynes per cm. lower than the former, but has decided advantages. The surface tension was lowered by use of 4 soaps carefully prepared from cocoanut-oil, olive-oil, castor-oil, and palmitic acid. The soaps gave stable solutions which did not alter the H-ion concentration of the medium. The soaps varied not only in the amount necessary to produce a given depression but in the actual depression possible. By use of these depressants a range in surface tension of broth from 30 to 53 dynes per cm. was obtained. The range in Uschinsky''s solution was 26.0 to 71.6 dynes per cm. while the range of Ashby''s solution was 34.8 to 74.2 dynes. A total of 17 organisms were employed in the study. It was found that the surface tension of broth rapidly changed as Escherichia coli developed. Differences in growth of the various organisms in broth of varying surface tension were ascribed to the chemical nature of the depressant and not associated with surface tension. The development of Azotobacter chroococcum and the amount of nitrogen fixed in solution of varying surface tension was not affected by the surface tension. The authors conclude that surface tension within the limits of the experiments described was not a factor in bacterial growth.

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