Autobiography of the winner of the 1952 Nobel Prize for Physiology and Medicine.

The soil and the plant. The microbe and its activities. The soil population and its distribution. Rôle of microbes in the decomposition of organic substances in the soil. Transformation of nitrogen by soil microbes. Transformation of mineral substances in soil through the direct or indirect action of microorganisms. Interrelationships between higher plants and soil microorganisms. Modification of the soil population. Importance of microbes in soil fertility.