THE Greek doctrine of the four humors colored all the conceptions of disease; upon their harmony alone it was thought that health depended. The four temperaments, sanguine, phlegmatic, bilious and melancholic, corresponded with the prevalence of these humors. The body was composed of certain so-called "naturals," seven in number—the elements, the temperaments, the humors, the members or parts, the virtues or faculties, the operations or functions and the spirits. Certain "non-naturals," nine in number, preserved the health of the body, viz. air, food and drink, movement and repose, sleeping and waking, excretion and retention, and the passions. Disease was due usually to alterations in the composition of the humors, and the indications for treatment were in accordance with these doctrines. They were to be evacuated, tenuated, cooled, heated, purged or strengthened. This humoral doctrine prevailed throughout the Middle Ages, and reached far into modern times—indeed, echoes of it are still to be heard in popular conversations on the nature of disease.

The Arabians were famous for their vigor and resource in matters of treatment. Bleeding was the first resort in a large majority of all diseases. In the "Practice" of Ferrari there is scarcely a malady for which it is not recommended. All remedies were directed to the regulation of the six non-naturals, and they either preserved health, cured the disease or did the opposite. The most popular medicines were derived from the vegetable kingdom, and as they were chiefly those recommended by Galen, they were, and still are, called by his name. Many important mineral medicines were introduced by the Arabians, particularly mercury, antimony, iron, etc. There were in addition scores of substances, the parts or products of animals, some harmless, others salutary, others again useless and disgusting. Minor surgery was in the hands of the barbers, who performed all the minor operations, such as bleeding; the more important operations, few in number, were performed by surgeons.