THE ANTIBIOTIC ERA--"Although more than 300 antibiotic substances have now been discovered, only five (penicillin, streptomycin, chloromycetin, aureomycin and terramycin) have attained the stature of major drugs. A handful of others have important, though limited, uses or are considered promising. All the rest have fallen short for one reason or another. Some are too weak; some work only in the test tube or on subhuman animals; most are too toxic. Naturally the search for potential new 'wonder' drugs goes on with undiminished fervor. The field for searching is very wide. There is hardly an area in the plant kingdom that has not yielded antibiotic substances: they have come from seed plants, lichen, many groups of fungi, the actinomycetes and bacteria."