Today, we talk about germs. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

That great master of American doggerel, Ogden Nash, wrote:

A mighty creature is the germ,
Though smaller than the pachyderm,
His strange delight he often pleases,
By giving people strange diseases.

Our knowledge of microbes is only three hundred years old. The Dutch lens maker Antonj Leeuwenhoek first observed them in the late 17th century. He called these small creatures animalcules, and he realized that they swam in any body of water.

But what about relating these small beasts to disease? A hundred and fifty years later, disease was rampant in London. Half the newborn babies died, and the death rate was far higher among the poor than the wealthy. Two things were clear by then. One was that London's drinking waters were, by and large, loaded with microorganisms. The other is that filth, particularly raw sewage, was to be found everywhere in poor areas.

It seems obvious to us that germs were causing the diseases. But germs, after all, swam in waters drunk by the well and the sick alike. Bad smells, on the other hand, were found in unhealthy neighborhoods, so people assumed that stench, or miasma, as it was called, caused disease. No one saw any reason to worry about the water. It was the stink people felt they had to get rid of.

Then, in 1849 and '53, London suffered terrible epidemics of cholera. A physician, John Snow, began looking at statistics. He worked doggedly among the sick and kept meticulous records of who'd died and exactly where they'd died. It took a long time, but Snow eventually found a high incidence of cholera among people who'd been drawing water from a pump called the Broad Street Well.

That made no particular sense until Snow realized that the cesspool of a tenement occupied by a cholera patient was next to the well. Contaminated water had leaked from the cesspool into the well's ground-water. Over protests, he managed to remove the handle from the well, and cholera abated in that part of London.

Snow's report soon led people to see that cholera was not caused by noxious gases, but by what was now called fecalized water. He put people on the track of the real agent of the disease. Four years later, Pasteur connected disease to bacteria. In 1865 Joseph Lister found he could kill disease-carrying bacteria during surgery by spraying a carbolic acid solution over the patient. Finally, thirty years after Snow pinpointed the Broad Street Well, the German physician Robert Koch showed how to make a disease-specific vaccine. He isolated the bacterium that caused anthrax and figured out how to make a vaccine to kill it.

It can take decades to overturn old thinking. The leap from unhealthy vapors to bacteria was still hard to make -- even after Snow used the Broad Street Well to show that a leap had to be made.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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A simple account of Snow's work is to be found in: Dubos, R., and Pines, M., Health and Disease. New York: Time-Life Books, 1965.

For a fascinating fictionalized account of John Snow and the Broad Street Well, see: Taylor, L. P., The Drummer was the First to Die. New York: St. Martins Press, 1992.

This is a greatly revised version of Episode 74.

Representation of germs in the 1911 Encyclopaedia Britannica