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midwives. Suspecting that the physicians were coming to women in labor with particles of corpses from the dissection room still on their hands, he got them to wash more thoroughly with a disinfectant and was able to show that antiseptic practice made a difference. No one paid any heed. A few years later, in 1860, Joseph Lister introduced antiseptic practice to the Glasgow Royal Infirmary, and postoperative putrefaction rates subsequently declined. The later discovery that infection with bacteria led to putrefaction provided a concept to explain these observations, but until then Lister, like Semmelweis, had trouble getting his colleagues to take his findings seriously.

      One of the weaknesses in these early manifestations of evidence- based medicine, as the examples of Pinel, Louis, Semmelweis, and Lister make clear, was their inability to shed much light on what lay behind the figures—they showed associations but explained nothing about cause. There are commonly tensions between broad associations of this type, the specific evidence that comes from laboratory experiments, the evidence of our own eyes, and what currently dominant theories may dictate. To the relief of most doctors, the tensions between broad associations and more specific evidence were eased to a degree with the emergence in the second half of the nineteenth century of laboratory science, which more clearly linked cause and effect.

       THE CAUSES OF DISEASES

      In the 1870s, a set of laboratory sciences emerged to form the bedrock of the new scientific and diagnostic work that would transform much of medicine and underlie the practice of doctors like Richard Cabot and the rise of hospitals such as Massachusetts General, as noted in chapter 1. Advances in bacteriology were among the key scientific developments that led to new treatments as well as hope that science would lead to further breakthroughs. In France, Louis Pasteur provided the first evidence that germs, later called bacteria, were the causative factors in a series of infections such as rabies,¹⁰ and he supplied both evidence and a rationale for vaccinations and antiseptic procedures.¹¹ In Germany, Robert Koch set up the first laboratory dedicated to the pursuit of the microbial causes of disease, and his most famous protégé, Paul Ehrlich, who more than anyone else developed the dyes that helped distinguish among bacteria, later developed the drugs that killed some of them. It was Ehrlich who coined the term magic bullet, for a drug that would specifically target the cause of an illness and leave the patient otherwise unaffected.¹² For generations afterward, until the 1960s, the glamour and importance of their discoveries and those of their successors, written up in books such as the Microbe Hunters, attracted students to medicine.¹³

      In 1877, Koch transmitted the lethal disease anthrax by injecting noninfected animals with the blood of infected animals; he then isolated anthrax spores and demonstrated that these spores, if grown in the eye of an ox for several generations, could also cause the infection. Where Lister met resistance for recommending an antiseptic approach in surgery on the basis of a comparison of the numbers of infections with and without antiseptic conditions, Koch could show the existence of bacilli under a microscope and later growing on a Petri dish, and then demonstrate the efficacy of sterilization in killing the bacillus. Where it had been difficult to overcome resistance to revolutionary ideas about antiseptics using only comparative numbers, for many seeing was believing.

      The impact on medicine of this new science of bacteriology and the germ theory of disease can be seen with wonderful clarity in the case of cholera. From the 1830s to the 1860s, before the role of germs in disease was recognized, a series of cholera epidemics struck Europe, killing tens of thousands. Because no one knew what caused this plague or how to protect themselves from a grisly death, there was widespread public panic. In 1856, in a now-celebrated series of investigations John Snow, a London physician, mapped the appearances of the disease around London. He made a connection between clusters of those with the disease and contamination of the water supply and famously recommended removal of the handle from the pump in Broad Street so residents would get their water from other sources.¹⁴

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