Health and Disease

The early modern period witnessed great changes in physical science, with the decline of Aristotelianism and the mechanization of the world picture during the period dubbed the scientific revolution. Notions of health and disease reflected some of these developments, although continuities are also obvious. Manuals of health and longevity became popular, as health became a desirable goal in societies now concerned with investigating the wider world and the stars above. As always, health was generally associated with moderation, especially through the regulation of what were called the six "nonnaturals": air, food and drink, sleep and wakefulness, retentions and excretions, motion and rest, and the affections of the mind. An Italian nobleman, Luigi Cornaro (c. 1463–1566), wrote in his old age a treatise on hygiene, based on his own experience of moderate living. It was widely translated and remained in print for several centuries. Although the explanatory framework would differ today, Cornaro's treatise is filled with advice that would not be out of place in a contemporary lifestyle medical manual.

There was much continuity in advice manuals on health for a long time after Cornaro, but ideas about the causes and mechanisms of disease began to change. Hippocratic humoralism had much staying power, but doctors such as Paracelsus (1493–1541) and Jan Baptista van Helmont (1579–1644) elaborated new medical systems. Van Helmont linked physiological function in both health and disease with a vital power that he identified with the archeus, a principle he associated with each organ. It had the effect of separating the disease from the body of the individual sufferer, as the archeus had some sort of independent existence. Van Helmont inclined toward chemical explanations of disease, but other doctors leaned toward mechanical models of both normal and pathological functions, following in the wake of the triumphant natural philosophers such as Galileo Galilei (1564–1642) and Isaac Newton (1642–1727). Iatrochemists and iatromechanists, as they were called, vied with each other for theoretical dominance from the late seventeenth century.

In the midst of all these theoretical concerns, one clinician remained true to Hippocratic humoralism. Thomas Sydenham (1624–1689), the "English Hippocrates," approached clinical medicine without much concern for the newfangled chemistry or mechanical physiology. He left superb descriptions of a number of diseases, including gout, smallpox, and hysteria, insisting that medicine was an empirical affair, ultimately based on careful observation and the trial-and-error use of remedies. One such remedy, Peruvian bark (which contains quinine), so impressed him in its capacity to extirpate "agues" (malarial fevers), that he came to believe that diseases could be classified in the same way that naturalists classified plants and animals. Nosology, or disease classification, became a preoccupation among eighteenth-century physicians. It came to be based primarily on symptoms, and the number of disease categories multiplied. Sydenham's remarks on the specificity of diseases came into their own in the late nineteenth century, when germ theorists began to identify the disease with the germ that was proposed as its causative agent.

Hippocratic humoralism gradually lost its persuasiveness during the eighteenth century, as doctors turned to the blood, nervous system, or glands as the primary foci of disease causation. At the same time, pathologists such as Giovanni Morgagni (1682–1771) began to note consistent patterns of structural changes in the bodies of patients they autopsied and to attempt to correlate these changes in the organs and tissues with the diseases they had diagnosed and the symptoms that the patient had suffered from during life. This clinicopathological correlation became the basis of the hospital medicine that flourished in Paris after the French Revolution.