THE LETHAL ACTION OF SUNLIGHT UPON BACTERIA IN SEA WATER

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Abstract
Numerous observations on the vertical, diurnal and seasonal distribution of bacteria in the sea off the coast of southern California reveal evidence of little or no bactericidal action of sunlight. While the seasonal fluctuation in the bacterial population is almost inversely proportional to the intensity of sunlight as recorded by a pyroheliometer, which may be indicative of a lethal action, there are multifarious other biological, physical, and chemical factors which must be considered in interpreting results. Laboratory experiments show that at this latitude mid-day summer sunlight had only a feeble lethal action on bacteria in the uppermost few mm. of sea water and even shallow layers of sea water are not sterilized by prolonged exposure. Virtually no bactericidal radiations penetrate sea water 3 m, and the intensity of the most abiotic rays is materially reduced by passage through 10 cm. of sea water.

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