Health and Disease

In order better to follow the course of disease in the living, French clinicians routinized systematic physical examinations of their patients. Jean Corvisart (1755–1821) developed percussion, tapping on the thorax and abdomen, to demarcate enlarged organs, collections of fluid, or tumors, and René Laennec [1781–1826] invented the stethoscope in 1816. Paris itself became a world center of medical education, and foreign students exported the French way of doing things throughout the Western world. French medicine was based primarily on the diseases of the organs, such as the heart, lungs, or liver. The development of better microscopes in the 1820s encouraged doctors to push pathological analysis into the tissues (a concept popularized by the French clinician M. F. X. Bichat [1771–1802]), and by the late 1830s, cell theories had been elaborated by German scientists such as Matthias Jakob Schleiden (1804–1881), for plants, and Theodor Schwann (1810–1882), for all living organisms. Rudolf Virchow's (1821–1902) Cellular Pathology (1858) put the cell at the heart of medical reasoning.

At about the same time, the work of microbiologists such as Louis Pasteur (1822–1895) and Robert Koch (1843–1910) showed the causative importance of bacteria and other microorganisms in a host of diseases. The germ theory of disease had dramatic practical spin-offs for medicine and public health, but it also separated the "disease" (the microorganism) and the victim of disease. Without the tubercle bacillus, there could be no tuberculosis. For some doctors, the disease could now be equated with its causative organism.

The germ theory was never without problems. Many clinicians considered germs as either incidental to or the result of disease, rather than its cause. Enthusiastic researchers found germs for many diseases, such as pellagra and cancer, which subsequent investigations would disprove. Some social activists complained that obsession with germs deflected concern from other factors that also influenced health, such as housing or inequalities of wealth. Why two individuals exposed to the same germ might have completely different reactions highlighted important host-parasite interactions. The range of agents causally associated with disease has been extended from the bacteria to include worms, plasmodia, amoebas, viruses, and, more recently, prions. Always, anomalies have driven researchers back to the bedside, community, or laboratory.

Since the mid-nineteenth century, the thrust of biomedical levels of disease explanation has been toward ever more minute categories: intracellular elements, chemicals, and molecules with known compositions and structures. Molecular biology is the preeminent science of the present day, created just before, but reaching powerful maturity after, the elucidation of the structure of DNA in 1953 by James Watson and Francis Crick. The biological importance of DNA had been recognized before Watson and Crick's work, but understanding its structure provided a model of how this long-chained molecule, found in the chromosomes of the cell's nucleus, controlled the inherited continuity that is characteristic of living organisms.

Modern biomedical research has revealed many of the mechanisms of disease at the molecular level. The first "molecular disease," sickle-cell anemia, was identified by Linus Pauling in 1949 as the result of a minor structural (but large functional) change in the hemoglobin molecule. Molecular medicine has progressed rapidly since the mid-twentieth century, with the Human Genome Project offering the prospect of much greater knowledge about the role of genetic factors in health and disease. Genetic information also creates a host of ethical problems, such as confidentiality, insurance premiums, employability, and advice on parenthood. Critics argue that it is eugenics in new dress; advocates insist that the knowledge itself is neutral and its use is a matter for society to sort out.

By the twenty-first century the concept of disease had been diluted, as we have all been medicalized. Acts, desires, and choices that in previous generations would have been conceptualized within moral, religious, or legal frameworks could now be attributed to disease. Eating disorders, suicide, many forms of criminality or deviancy, stress, and many other "facts" of modern life are often included within disease categories. Homosexuality has been a normal stage of the life cycle, a sin, a crime, a disease, and a life choice in different periods within Western society. "Mental" diseases continue to carry a moral burden.

If modern medicine has been expansionist in the field of disease, it has been less successful in assimilating health into its orbit. The more we know, the more prevalent disease, or potential disease, seems to be. Orthodox medical advice about health is largely statistical in its foundations and behavioral, not medical, in its recommendations. The Hippocratic injunction to moderation is still at the heart of Western medicine. What is "normal"—that is, healthy—is often based on epidemiological surveys, actuarial information, and cultural values. Despite the enormous power of modern biomedicine, health and disease still have important cultural, aesthetic, and moral dimensions to them.