The influence of philosophy and the natural sciences became also more and more marked. At the head of its philosophers must be placed Leibnitz (164:6-1716), who, by his own writings and those of his pupils, created a philosophical school, whose influence is still every where felt. His doctrine was dualistic: Matter is created once for all, and has no further need of the Creator. As concerns the spiritual world, he assumed minute, indivisible, intelligent beings, called monads,—constituents of all bodies and all beings. In close relation with him stood Kant, while in England Locke and Hume became leaders of the opposed and materialistic school, declaring the brain to be an organ for the secretion of thought.
Among the universities founded during the eighteenth century were those of Breslau, 1702; Bonn, 1771; Stuttgart, 1781; Pesth, 1794; Gottingen, 1737; and Erlangen, 1743. Medicine was also cultivated in learned societies, which increased constantly in numbers. In 1744 Frederick the Great united two other societies into his Royal Academy. In Switzerland, in 1751, was founded an association of physicians and naturalists, while in France royal scientific societies were founded at Bordeaux, Montpellier, Lyons, and Dijon, and the Royal Medical Society of Paris lived from 1717 until 1788. In spite of all these opportunities for enlightenment, everything was not yet enlightened. Then de Haën defended the existence of demons, and Maerz, a well-known theological teacher, in 1760 devoted a book to witches and magic. That witches were burned publicly is a matter of history, even in America. So late as 1821 there was a statute regarding witches in Ireland, and they were burned in Mexico as recently as 1877. But these are flying pictures of the eighteenth century, which are meant only for the moment to illustrate the more serious topic, to which we must now address ourselves.
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First of all, the medical systems and theories of the century. Many hundred years previously Galen had originated a method, which deserves, perhaps, the title of pure eclecticism. The first purely eclectic system similar to his originated with Boerhaave (1688-1738), perhaps the most famous physician of his or any other century. He was the son of a clergyman near Leyden, Holland, and was one of thirteen children. Originally intended for the clerical profession, he had studied philosophy, history, logic, metaphysics, philology, mathematics, as well as theology, with great diligence. His education was, later, directed to the study of medicine, because of the statement that the purity of certain theological doctrines was endangered by him. So he studied chemistry and botany, and then anatomy and medicine, graduating in 1693. He practiced in Leyden with great success, and was offered a court position. In 1709 he was tendered the chair of Medicine and Botany, and in 1714 that of the Practice of Medicine; in 1718 he was also made Professor of Chemistry. In all of these positions he displayed the greatest capacity. He was a clinical teacher of rare talent, and soon acquired such reputation as to attract to Leyden students from all parts of the world in such numbers that no lecture-room in the university could contain them. He was the first to give separate lectures on the subject of ophthalmology, and employed the magnifying-glass in examining the eye. As a practitioner he was no less popular, and he left an estate valued at two million dollars. He was so famous that, when a Chinese official addressed a letter "To the Most Famous Physician in Europe," it reached him safely. He made no distinction in his patients, and compelled Peter the Great to wait a whole night for his turn to consult him. His most eminent pupils were: Haller, Van Swieten, de Haën. Gaub, and Cullen.
Boerhaave's influence and dignity, which were astonishing, even in a physician, were based no less upon his encyclopaedic attainments than upon the benevolence and purity of his character. He was free from disputatiousness and vanity, although everywhere regarded as an oracle. His universal maxim was: "Simplicity is the seal of truth," although he never manifested this in his therapeutics. He employed the thermometer in the axilla in examining his cases, as did the iatrophysicists of the previous century.
His doctrines did not form a new system, but rather a composite of earlier systems, he stands also in the anomalous position of one who had the whole world at his feet, and yet contributed little or nothing which has been of essential importance. In fact, his peculiar views have been so universally given up that they are of only meagre historic interest. He looked upon disease as a condition in which bodily action or natural activities, being disturbed or unsettled, could take place only with difficulty; the reverse of this, of course, constituted good health. Fever he regarded as an effort of Nature to ward off death. Digestion was explained, like the circulation, upon mechanical principles. In his therapeutics, besides his efforts to sweeten the acid, to purify the stomach, to get rid of acridities, he made Hippocrates and Sydenham his models. His biographers say that his medicines were less effective than his personal appearance. He left many adherents, but no school of followers. It must be said, however, to his credit, that, while not the first to give clinical instruction, he permanently established a clinical method in teaching.
Gaub (1705-1780), professor in Leyden from 1731, was but little inferior to his master, Boerhaave, in fame as a teacher. He wrote the first complete work on the exclusive subject of general pathology. In general therapeutics he considered the healing power of Nature amply sufficient to remove sickness, but attributed this power sometimes to the soul and sometimes to the body.
There arose, naturally, strenuous opposition to the views and teachings of Boerhaave, and his principal opponent was Stahl (1660-1734), who was one of the most important systematists of any age, a profound thinker, and a pioneer chemist. He began lecturing in Jena at once upon his graduation, at the age of twenty-five, and moved through two or three different university positions until he came to Berlin at the age of fifty-six. He was a great pietist, of uncouth manners, faithful to his laboriously acquired convictions, and bitter and relentless against those who could not accept them. Indeed, he regarded his convictions as revelations from God. He looked upon the success of another as a personal injury to himself, and from being first a croaker he became finally a confirmed misanthrope, until he fell into actual melancholia. Pecuniary profit he had never sought, and its pursuit he scorned. His views were dynamico-organic, pietistic, and antagonistic. He regarded the soul as the supreme principle, life-giving and life-preserving, not to be confounded with the spirit; when hindered or obstructed in its operation, disease was present. The soul governed the organism chiefly by way of the circulation; consequently, plethora played an important rôle. To get rid of this plethora the soul employed either fever or convulsive movements; for example, in children plethora produces a pressure of blood to the head, and, by way of compensation, the soul provides a haemorrhage from the nose. For reasons easily appreciated, he regarded bleeding piles as safety-valves of the utmost importance. Fever was a salutary effort of the soul to preserve the body; this was true even of intermittents, and, accordingly, he never gave cinchona. He scorned anatomy and physiology, saying, in one place, that medicine had profited as much by the knowledge of the bones in the ear as by a knowledge of snow which had fallen ten years previously. But Stahl was one of the most eminent chemists of the age, and did a great deal to liberate chemistry from the glamour of alchemy and the domination of pharmacy, and to transform it into an independent science.