The Dutch microscopist Anton van Leeuwenhoek (1632– 1723) laboriously ground small but excellent lenses, which gave him a better view of the world of tiny objects than anyone else in his time had had. In 1677, he placed ditch water at the focus of one of his small lenses and found living organisms too small to see with the naked eye but each one as indisputably alive as a whale or an elephant—or as a human being. These were the one-celled animals we now call “protozoa.” In 1683, van Leeuwenhoek discovered structures still tinier than protozoa. They were at the limit of visibility with even his best lenses, but from his sketches of what he saw, it is clear that he had discovered bacteria, the smallest cellular creatures that exist. To do any better than van Leeuwenhoek, one had to have distinctly better microscopes and these were slow to be developed. The next microscopist to describe bacteria was the Danish biologist Otto Friedrich Müller (1730–84) who described them in a book on the subject, published posthumously, in 1786. In hindsight, it seems that one might have guessed that bac- teria represented Fracastoro’s infectious agents, but there was no evidence of that and even Müller’s observations were so borderline that there was no general agreement that bacteria even existed, or that they were alive if they did. The English optician Joseph Jackson Lister (1786–1869) developed an achromatic microscope in in 1830. Until then, the lenses used had refracted light into rainbows so that tiny objects were rimmed in color and could not be seen clearly. Lister com- bined lenses of different kinds of glass in such a way as to remove the colors. With the colors gone, tiny objects stood out sharply and in the 1860s, the German botanist Ferdinand Julius Cohn (1828–98) saw and described bacteria with the first really convincing success. It was only with Cohn’s work that the science of bacteriology was founded and that there came to be general agreement that bacteria existed. Meanwhile, even without a clear indication of the existence of Fracastoro’s agents, some physicians were discovering methods of reducing infection. The Hungarian physician Ignaz Philipp Semmelweiss (1818–65) insisted that childbed fever which killed so many moth- ers in childbirth, was spread by the doctors themselves, since they
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Isaac Asimov on the History of Infectious Disease — And How Humanity Learned To Fight Back
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