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THOSE odd-shaped objects in the background of this week's TIME cover are viruses-magnified more than 50,000 times and reproduced in their actual shape by machine and man. The viruses, which are measured in millionths of an inch, were first photographed by an electron microscope that produces an enlarged image of minute particles through the use of a beam of electrons. Working from electron-micrograph prints, Artist Bernard Safran enlarged the viruses somewhat more to obtain the proper effect for the cover. Among those he chose to use, the sticklike viruses at upper left...
...appeared in 1938: the electron microscope, in which beams of electrons are focused sharply enough to take photographs of objects less than a millionth of an inch across. This made many virus particles visualizable-and another Rockefeller fellow had something to visualize. Indiana-born Wendell Stanley went back to Beijerinck's favorite, the tobacco mosaic virus, or TMV, and spent years in a Princeton laboratory cooking down a ton of sickly tobacco leaves, filtering and re-filtering, dissolving and redissolving, until he had isolated the cause of this economically costly disease. What he had to show for years...
Stanley thus gave a crystal-clear answer to the question: What is TMV? Electron micrographs showed thin rod-shaped crystals, little more than a hundred-thousandth of an inch long. This answer raised an intriguing new question. Is a virus animate or inanimate, living or dead, animal or mineral? Dr. Stanley's way out of the dilemma is to broaden the definition of "living'' to include any particles that are capable of reproducing or replicating themselves. That covers viruses...
...Tulip." Thanks largely to chemists like Stanley (who now runs the University of California's Virus Laboratory) and the electron microscopists, a virus can now be defined as an infectious particle that has no metabolism of its own and reproduces itself only by taking over the metabolic processes of the living cell it invades. Viruses are the ultimate parasites. They parasitize everything in nature from bacteria and flowering plants up through invertebrates such as mosquitoes, and the vertebrates from fish, amphibians, reptiles, birds and mammals...
...Closer Look. Thus viruses got defined and classified. But just how the virus core gets into a cell remained a mystery, even after Dr. Robley C. Williams, a member of Stanley's California team, devised the method of plating the particles with gold or uranium to get clearer electron micrographs. Then, two years ago at Cambridge University's Cavendish Laboratory, Drs. Sydney Brenner and Robert W. Home made an illuminating refinement on electron micrography, revealing far more intimate details of virus structures and differences, and clues to how viruses work...