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Abstract
The effects of different concentrations of d (–) threo and l (+) threo-chloramphenicol on the growth of Scenedesmus quadricauda have been studied. The results indicate: (a) both isomers caused an increase in the total population largely independent of concentration; (b) at concentrations between 100–200 μg./ml. both isomers gave a secondary increase in growth after a secondary lag period of 4–6 days; (c) both isomers inhibited the growth rate at concentrations comparable with those which inhibit bacterial growth and protein synthesis. The l (+) threo isomer was twice as effective as the d (–) threo isomer, though it did not give any inhibition below 22 μg./ml. (d) above 50 μg./ml. the d (–) threo isomer gave a significantly greater lag period than below this concentration. The l (+) threo isomer did not affect the lag period below 25 μg./ml., but above this concentration, an increase in the concentration lengthened the lag period at the same rate as with the d (–) threo isomer above 50 μg./ml.
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