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Although several investigators have studied the effect of concentration of organic nutrients upon the growth of microorganisms, most of the experiments have been concerned with concentrations which are much higher than those which occur in soil solutions, sea water and other natural environments. Ac-cording to Rahn (1932) the concentration of food does not influence the rate of growth of bacteria except when the concentration is very low, 0.01 to 0.1 per cent. Penfold and Norris (1912), Hucker and Carpenter (1927), Friedlein
ZoBell et al. (Tue,) studied this question.