The Green Invader

The great Cro-Magnon paintings in the famous Lascaux Cave in France were done at least 15,000 years ago, but in the 15 years since the cave became a major tourist attraction, the paintings have been in greater danger than in all those previous centuries. In 1960 guards noticed that two green spots had formed on a wall, though fortunately a good way from the paintings. By 1962, there were 15 colonies of this green growth, thought to be an alga called Chlorella vulgaris that depended on the newly introduced light. When the number of colonies jumped to 93, with several of them spreading toward the fantastic, sway-backed creature known as the Unicorn, the Ministry of Cultural Affairs took alarm. Last April it ordered the cave closed for three months, partly to study the effects of darkness. Last week the scientists reported that if Lascaux, which has been called "the Sistine Chapel of prehistoric art," is to survive at all, the cave will have to be shut indefinitely.

What had happened was that, in its measures to assure the paintings the same kind of humidity and temperature control that museums give to their treasures, the Ministry had inadvertently opened the door to something worse than Chlorella. Unfiltered air currents brought into the cave microorganisms that settled on the walls. (Says Biologist Pierre Grasse, one of the rescue team: "There are as many microbes in the cave as in the Metro during rush hour.") Such microorganisms are the natural food of chlorobotrys, an alga that can live without light. Chlorobotrys is thus the major threat. "We could rid the cave of algae in no time," says Grasse, "if we just dried it out completely. But then the limestone would dry out, too, and the precious paintings would gradually flake away." The scientists are now working against time with antiseptics, and plan to install what they hope will be effective filtered ventilation. But the green invader has penetrated deep into crevices that the antiseptics cannot reach; it has protected itself with a sticky jelly; and some of it is invisible anyway, making it necessary to treat the whole surface of the cave whether patently green or not.

As one fateful precaution, the scientists have decided to have the cave photographed down to the last millimeter. "With these photographs," says Grasse philosophically, "any museum or community in the world can reconstruct Lascaux."

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