ANTIBIOTICS AND VIRUSES

Some tiny plant organisms produce substances which are capable of killing bacteria, and penicillin and streptomycin are two examples of these. The organisms producing these useful antibiotics are in fact fungi, and are cultivated by man in order to obtain large quantities for treating diseases. Viruses are organisms which are very much smaller even than bacteria and very little is known about them. They seem to be on the borderline between the living and non-living although they do have the ability to increase and spread. They cause many diseases to plants and animals and in man are thought to be responsible for such things as colds, influenza and measles. In plants they produce disorders such as wrinkling and yellowing of leaves. They seldom kill plants, but completely upset their normal way of life, and because they can ruin crops are a problem to man. Unlike a lot of bacterial and fungal diseases in plants, they cannot be killed by chemical sprays.