Universal Enemy

On the border line between the living and nonliving hovers a mysterious invisible substance: the virus. Some scientists think the virus is the most primitive form of life; others insist it is a heavy protein molecule, with complex chemical reactions, a kind of crystal which exists as a parasite on living tissue. But whatever the nature of the virus, one fact is certain: it is the foe of all living things, from microbe to man.

Last week famed Biologist Kenneth Manley Smith of Cambridge University published a full account of this hostile force called The Virus, Life's Enemy (Macmillan, $2). Salient facts:

> Main virus diseases in man are the common cold, smallpox, yellow fever, measles, mumps, chicken pox, influenza, encephalitis (sleeping sickness), infantile paralysis. The animals' viruses bring foot-and-mouth disease, distemper, swine fever, parrot fever, pox diseases of birds. Fish and insects are also attacked by viruses, and no fewer than 135 plant-virus diseases have been described. Most prevalent: tobacco mosaic disease, potato leaf roll, sugar beet curly top. Viruses flourish only in living tissues, cannot be cultured in test tubes.

> Although few viruses have ever been seen, scientists have measured many of them, and can identify them by pattern, in much the same way as a blind man knows the shape of his furniture by groping around. Viruses are measured in several different ways. One is to strain a substance known to contain a virus (like sap from a diseased plant) through a filter with pores of submicroscopic size. The smallest virus, that of foot-and-mouth disease, is ten-millionths of a millimeter in diameter.

> Viruses do not grow as independent molecules, but enter into a dynamic relationship with their hosts. For example, in certain rabbit tumors, the viruses entrench themselves in a group of cells. The animal's body may react by destroying the cells which harbor the virus. Once the host cells are destroyed, the tumors gradually disappear.

> Viruses may be spread by air, wind, moisture droplets, insects. Many viruses, like that of tobacco mosaic, can be dried out, yet retain their potency for many years. Their operations are exceedingly delicate. King Edward potatoes, for example, are all infected with virus, but are immune to it. When King Edward plants are grafted on to other potatoes, they die.

> Perhaps viruses are related to genes, the basic units of heredity. For genes also seem to be active chemicals which can duplicate themselves. Some scientists also suspect that viruses are the agents which cause cancer in man, for they often stimulate cells to abnormal, erratic growths.

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