Living Electron Pictures

Electron microscopes are much more powerful than microscopes using light, but conventional models have a great disadvantage: they cannot be used on living cells or organisms. Their pictures of bacteria, for instance, show dried-up husks that do not resemble living bacteria any more than ancient Egyptian mummies resemble living men. But last week a new-type electron microscope in Toulouse, France, was taking pictures of bacteria that are still alive and reasonably healthy.

An electron microscope works by shooting electrons through an object and bringing them to a magnified focus on the far side. The object shows as a shadowed picture because some parts of it stop more electrons than others. Since electrons are scattered by air, the interior of the instrument must be an almost perfect vacuum, which would dry up and kill almost instantly all living bacteria.

The new French microscope at the Toulouse Electron Optics Laboratory is housed in a shining aluminum sphere 78 ft. in diameter. Professor Gaston Dupouy, head of the laboratory and the microscope's chief operator, explains that he protects bacteria by enclosing them in a tiny air-filled cell that fits on the microscope's stage. The cell has two windows, one on the top, the other on the bottom, which are covered with collodion film less than four-millionths of an inch thick. The windows are so small (four-thousandths of an inch in diameter) that this gossamer stuff has enough strength to resist the suck of the vacuum. So the cell keeps its moist air and the bacteria in it do not dry up.

The 50,000-volt electrons of ordinary microscopes are not powerful enough to penetrate the two layers of film and the plump, water-filled bodies of healthy bacteria. So the upper part of Dupouy's sphere is filled with a powerful accelerator that delivers a beam of million-volt electrons. They are tricky and dangerous to handle, but carefully measured bursts of them pass through living bacteria and make meaningful shadow pictures of their insides, magnified 25,000 times. The bacteria are little the worse for their experience. Dupouy testified almost affectionately that when they are taken out of the formidable microscope, they can still reproduce their kind.

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