In learning to utilize antibiotics for the control of human and animal diseases, the medical and veterinary professions have acquired powerful tools for combating infections and epidemics.

The discovery of streptomycin as a product of a rather obscure group of microorganisms, the actinomycetes, led to the study of these organisms as potential producers of other chemotherapeutic substances.

The soil is not a mass of dead debris, merely resulting from the physical and chemical weathering of rocks; it is a more or less homogeneous system which has resulted from the decomposition of plant and animal remains. It is teeming with life.

With the exception of autotrophic bacteria, the green, or chlorophyll-bearing, plants are the only living forms on this planet capable of synthesizing organic matter out of inorganic elements and simple compounds.