Today, let's 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, once 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 just over 300 years old. They were first observed in the late 17th century by the Dutch lens-maker Antonj Leeuwenhoek. He found that these tiny "animalcules," as he called them, swam in any body of water.

But what about relating these small beasts to disease? 150 years later, disease was rampant in London. Half the newborn babies died, and the death rate was far higher among the poor than among the wealthy. Two things were also clear by then. One is that London's drinking waters were, by and large, simply loaded with microorganisms. The other is that filth -- particularly raw sewage -- was to be found everywhere in poor areas.

It's obvious enough to us that germs were causing the diseases. But germs, after all, swam in waters drunk by both the well and the sick. What was obvious was that bad smells were found in unhealthy neighborhoods. It seemed clear that stench, or "miasma" as it was called, caused disease -- not the water. It was the stink that people felt they had to get rid of.

Then in 1849 and 1853 London suffered terrible epidemics of cholera. In 1853, a physician named John Snow started looking at statistics. He found a high incidence of cholera among people who'd been drawing water from a source called the Broad Street Well. Then he found that the cesspool of a tenement occupied by a cholera patient leaked into the Broad Street Well.

Snow's report soon caused people to see that cholera wasn't 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. In 1857 Pasteur connected disease to bacteria, and in 1865 Joseph Lister found that he could kill disease-carrying bacteria during surgery by spraying a carbolic acid solution. Finally, in 1882, 29 years after Snow pinpointed the Broad Street Well, the German physician Robert Koch showed us how to make a disease-specific vaccine. Koch, who'd found the bacterium that caused anthrax, figured out how to make a vaccine to kill it.

Scientific discovery is like that. It can take decades for people to overturn their old thinking. The leap from unhealthy vapors to bacteria was still a hard leap to make, even once the Broad Street Well showed 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.

(Theme music)

Dubos, R., Pines, M., Health and Disease, New York: Time-Life Books, [date not known]

This episode has been greatly revised as Episode 1490.