1. A definite relationship between the reproductive rate of a soil amoeba, Hartmanelia hyalina, and the available bacterial food supply has been demonstrated.

2. It has been shown that three species of soil bacteria have different feeding values not only in respect to the rate of division of the amoeba, but also in respect to the total increase in the amount of protoplasm.

3. The bearing of these results on the soil economy is discussed.

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