Louis Pasteur's Relentless Hunt for Germs in the Air

Louis Pasteur was at his most comfortable when working in his Paris laboratory. It was there that he had some of his greatest scientific triumphs, including experiments that helped confirm germs can cause disease.

- CARL ZIMMER

"Everything gets complicated away from the laboratory," he once complained to a friend. But in 1860, years before he became famous for developing vaccines and heating milk to kill pathogens, Pasteur ventured to the top of a glacier, on a remarkable quest for invisible life.

He and a guide began at the base of Mont Blanc in the Alps, hiking through dark stands of pines. Behind them, a mule carried baskets of long-necked glass chambers that sloshed with broth. They ascended a steep trail until they reached Mer de Glace, the sea of ice. The wind blew briskly over the glacier, and the vale echoed with the sound of frozen boulders crashing down the slopes. Pasteur struggled to make out the path in the glare of sunlight bouncing off the ice. When the scientist reached an altitude of 2,000 meters, he finally stopped. He removed one of the glass chambers from the mule's pack and raised it over his head. With his free hand, he grabbed a pair of tongs and used them to snap off the end of the neck. The cold air rushed inside the container.

The sight of Pasteur holding a globe of broth over his head would have baffled other travelers visiting Mer de Glace that day. If they had asked him what he was doing, his answer might have seemed mad. Pasteur was on a hunt, he later wrote, for "the floating germs of the air."