by Will Durant
An old and popular notion received in 1668 the first of several shocks when Francesco Redi of Arezzo published his Esperienze intorno alia generazione degli insetti—experiments tending to disprove abiogenesis, or the spontaneous generation of living organisms from nonliving matter. Until the second half of the seventeenth century it was almost universally believed (William Harvey an outstanding exception) that minute animals and plants could be generated in dirt or slime, and especially in decaying flesh; so Shakespeare spoke of “the sun breeding maggots in dead dogs.” 59 Redi showed that maggots did not form on meat that was protected from insects, but did form on meat exposed. He formulated his conclusion in the phrase Omne vivum ex ovo—“Every living thing comes from an egg or a seed.” When protozoa were discovered, the argument for abiogenesis was revived; Spallanzani answered it in 1767, and Pasteur again in 1861.
The discovery of those single-celled organisms which were later termed protozoa was the major contribution of this age to zoology. Anton van Leeuwenhoek was a Dutchman of Delft, but he reported through the Royal Society at London his scientific results through forty of his ninetyone years. Coming of a family of rich brewers, he was able to accept employments that offered him more leisure than pay, and he gave himself with fascinated pertinacity to studying the new world of life revealed by the microscope. He had 247 of these instruments, most of them made by himself, and his laboratory sparkled with 419 lenses, some of which may have been ground by Spinoza, who had been born in the same year (1632) and the same land as he. Peter the Great, when in Delft in 1698, made it a point to peer through Leeuwenhoek’s microscopes. When (1675) the scientist turned one of these to the study of some rain water that had fallen into a pot a few days before, he was astonished to see “little animals appearing to me ten thousand times less than those represented by Mons. Swammerdam and by him called water fleas or water lice, which may be perceived in the water with the naked eye”; 60 and he proceeded to describe an organism that we now recognize as the bell animalcule (Vorticella). This was apparently the earliest description of a protozoon. In 1683 Leeuwenhoek discovered still tinier organisms—bacteria. He found them first on his own teeth, “though my teeth,” he protested, “are kept usually very clean”; and he startled some neighbors by examining their spittle and showing them, under the microscope, “a great many living creatures” therein. 61 In 1677 he discovered spermatozoa in semen. He marveled at nature’s profuse equipment for reproduction: in a small quantity of human semen he estimated a thousand spermatozoa; and he calculated that in the milt of a single codfish there were 150 billion sperm—more than ten times the number of inhabitants that the earth would contain if all the land were as thickly populated as the Netherlands.
Jan Swammerdam was five years younger than Leeuwenhoek, but preceded him by forty-three years to the grave; he was a man of nerves, passions, ailments, and fluctuating purposes, who stopped his scientific work at thirty-six and burned himself out at forty-three (1680). He was intended for the ministry, but abandoned theology for medicine. Having secured his medical degree, he devoted himself to anatomy. He became enamored of bees, and especially of their intestines; he spent his days in dissecting them, his nights in reporting and illustrating his findings. When he had finished his classic treatise on bees (1673) he broke down physically; soon thereafter he gave up science as too worldly a pursuit, and returned to religion. Fiftyseven years after his death his manuscripts were collected and published as Biblia Naturae, the Bible of nature. This contained, in remarkably exact detail, the life history of a dozen typical insects, including the May fly and the honey bee, and microscopic studies of the squid, the snail, the clam, and the frog. Here, too, were descriptions of the experiments by which Swammerdam proved that muscles in tissues cut off from an animal’s body could be made to contract by stimulation of the connecting nerve. Like Redi he rejected abiogenesis; he went further, and showed that instead of decaying flesh producing minute organisms, it is these that produce decay in organic matter. In his brief career Swammerdam founded modern entomology, and established himself as one of the most accurate observers in the history of science. His return from science to religion personified the hesitation of modern man between a search for truth that smiles at hope and a retreat to hopes that shy from truth.
IX. ANATOMY AND PHYSIOLOGY
The human body, subjected to the microscope, gave up some of its intimate secrets to the advancing army of science. In 1651 Jean Pecquet of Paris traced the course of the lacteal vessels; in 1653 Olof Rudbeck of Uppsala discovered, and Thomas Bartholin of Copenhagen described, the lymphatic system; and in 1664 Swammerdam detected the lymphatic valves. In that year his friend Regnier de Graaf demonstrated the function and operation of the pancreas and the bile. In 1661 Nicolaus Steno, another friend, discovered the duct (still bearing his name) of the parotid gland, and a year later the lachrymal ducts of the eye. Graaf studied especially the anatomy of testicles and ovaries; in 1672 he gave the first account of those ovum-bearing sacs which Haller in his honor called the Graafian follicles. Bartholin left his card on two oval bodies adjoining the vagina, and William Cowper (physician, not poet) found (1702), and gave his name to, the glands that discharge into the urethra. Franciscus Sylvius (beloved teacher of Graaf, Swammerdam, Steno, and Willis at Leiden) left his signature on a fissure of the brain (1663). Thomas Willis, a founder of the Royal Society, published in 1664 a Cerebri Anatome which was the most complete account yet given of the nervous system; his name is still borne by the “circle of Willis,” a hexagonal network of arteries at the base of the brain.
The outstanding anatomist of the age was Marcello Malpighi. Born near Bologna in 1628, he took his degree in medicine there; after some professorial years in Pisa and Messina he returned to Bologna, and taught medicine in the university for twenty-five years. After working on the microscopic anatomy of plants he turned his lenses upon the silkworm, and recorded his findings in a classic monograph. In this investigation he nearly lost his eyesight; nevertheless, “in performing these researches,” he wrote, “so many marvels of nature were spread before my eyes that I experienced an internal pleasure that my pen could not describe.” 62 He must have felt like Keats first looking into Chapman’s Homer when (1661) he saw, in the lungs of the frog, how the blood passed from the arteries into the veins through vessels so fine that he called them “capillaries”; he found a network of such “little hairs” wherever arterial became venous blood; now, for the first time, the circulatory system was demonstrated in its course.
This was but a part, though the most important, of Malpighi’s contributions to anatomy. He was the first to prove that the papillae of the tongue are organs of taste; the first to distinguish the red corpuscles in the blood (but he mistook them to be globules of fat); the first to give an accurate account of the nervous and circulatory systems in the embryo; the first to describe the histology of the cortex and the spinal cord; the first to make possible a practical theory of respiration by describing with precision the vesicular structure of the lungs. Justly his name is scattered over our flesh in the “Malpighian tufts,” or loops of capillaries, in the kidneys, in the “Malpighian corpuscles” of the spleen, in the “Malpighian layer” of the skin. Many of his revelations and interpretations were challenged by his contemporaries; he defended himself vigorously, and won his battles at some cost to his nerves. As if laying these matters before the supreme court of science in his age, he sent to the Royal Society at London an account of his labors, discoveries, and controversies; the Society published this as his autobiography. In 1691 he was appointed personal physician to Pope Innocent XII, but he died in 1694 of an apoplectic stroke. His detection of the capillaries is one of the landmarks in the history of anatomy; his work as a whole established the science of histology.
As anatomical research progressed it revealed so many similarities between human and animal organs that some students were led close to a theory of evolution. Edward Tyson (whose name is given to the sebaceous glands of
the foreskin) published in 1699 Orang-Outang, she Homo Sylvestris, describing the orangutan as a “man of the woods”; he compared the anatomy of man with that of the monkey, and reckoned the chimpanzee to be intermediate between the two. Only the fear of a theological earthquake kept biology from anticipating Darwin in the seventeenth century.
From anatomy and structure the researchers passed to physiology and function. Till about 1660 respiration had been interpreted as a cooling process; now the experimenters likened it to combustion. Hooke proved that the essence of respiration is the exposure of venous blood to fresh air in the lungs. Richard Lower, also of the Royal Society, showed (1669) that venous blood could be changed to arterial by aeration, and that arterial blood became venous when persistently kept from contact with air. He suggested that the chief agent in aeration is a “nitrous spirit” in the atmosphere. Following these leads, Lower’s friend John Mayow described this active factor as “nitro-aerial particles.” In respiration, he believed, the nitrous particles are absorbed from the air into the blood; hence air exhaled is lighter in weight and less in volume than the same air inhaled. Animal heat is due to the union of nitrous particles with combustible elements in the blood; increased heat after exercise results from the extra intake of nitrous particles through increased respiration. These nitrous particles, said Mayow, play the leading role in the life of animals and plants.
The interpretation of vital processes led to one of the most indestructible controversies in the history of modern science. As physiology delved more and more curiously into the human anatomy, one after another function of the body seemed to yield to a mechanical interpretation in terms of physics and chemistry. Respiration appeared to be a combination of expansion, aeration, and contraction; the functions of the saliva, the bile, and the pancreatic juice were obviously chemical; and Gian Alfonso Borelli apparently brought to completion (1679) the mechanical analysis of muscular action. Steno, the fervent Catholic, adopted the mechanical view of physiological processes, and dismissed as “mere words meaning nothing” such vague phrases as Galen’s “animal spirits.” Descartes’ conception of the body as a machine seemed now fully justified.
Nevertheless most scientists felt that these bodily mechanisms were merely the instruments of some vital principle beyond analysis in physicochemical terms. Francis Glisson, a founder of the Royal Society, ascribed to all living substance a characteristic “irritability”—susceptibility to stimulation—which he thought to be absent from nonliving matter. Just as Newton, after reducing the cosmos to mechanism, ascribed the initial impetus of the world machine to God, so Borelli, after giving a mechanical explanation of the muscular processes, posited within the human body a soul from which all animal motion took its origin. 63 Claude Perrault, architect and physician, suggested (1680) that physiological actions that now seem mechanical were formerly voluntary, guided by a soul, but became mechanical through frequent repetition, like the formation of habits; perhaps even the heart had once been controlled by the will. 64 Georg Stahl argued (1702) that the chemical changes in living tissue are different from those seen in laboratories, for in living animals, he believed, the chemical changes are governed by an anima sensitiva which pervades all parts of the body. The soul, said Stahl, directs every physiological function, even digestion and respiration; it builds each organ, indeed the whole body, as an instrument of desire. 65 Diseases, he surmised, are processes by which the soul strives to remove something that hinders its operations; and he foreshadowed a twentieth-century “psychosomatic” theory by holding that disturbances of the “sensitive soul” can produce bodily ailments. 66
In one form or another vitalistic conceptions held the ascendancy in science till the second half of the nineteenth century. They yielded for a time to the rising prestige of mechanical physics; and they were revived, with the charm of literature, in Bergson’s Creative Evolution (1906). The debate will go on until the part understands the whole.
X. MEDICINE
The strongest stimulus to the biological sciences came from the needs of medicine. Botany, before Ray, had been the handmaiden of pharmacy. Health was the summum bonum, and men, women, and children sought it through prayers, stars, kings, toads, and science. One physician, before prescribing, “went to his closet to pray,” says Aubrey, 67 so that at last “his knees were horny” with orisons. Astrology still took a hand in medicine; the surgeon in ordinary of Louis XIV advised that the King be bled only in the first and last quarters of the moon, “because at this time the humors have retired to the center of the body.” 68 Defoe thought that the money spent upon quacks would have paid off the national debt. 69 Flamsteed, the astronomer royal, traveled miles to have his back stroked by the famous quack Valentine Greatrakes, who proposed so simply to cure scrofula. Perhaps Flamsteed was among the 100,000 whom Charles II touched for scrofula—the “King’s evil.” In the one year 1682 the complaisant ruler touched 8,500 sufferers; in 1684 the press to get to him was so great that six of the sick were trampled to death. William III refused to go on with the play. “It is a silly superstition,” he exlaimed when a crowd besieged his palace. “Give the poor creatures some money, and send them away.” On another occasion, when he was importuned to lay his hand on a patient, he yielded, but said, “God give you better health and more sense.” The people denounced him as an infidel. 70
Defects of personal hygiene and public sanitation co-operated with the resilient ingenuity of disease. Prostitution spread syphilis in cities and camps. It was especially rife among actors and actresses, as we gather from a subtle story in Mme. de Sévigné of “a player who, being resolved to marry though he labored under a certain dangerous disorder, one of his companions said to him, ‘Zounds! can’t you wait till you are cured? You will be the ruin of us all.’” 71 The French general Vendôme appeared at court without a nose, having sacrificed it to the spirochetes. 72 Cancer was on its way; Mme. de Motteville describes a cancer of the breast. 73 Yellow fever was first described in 1694. Smallpox was especially widespread in England; no cure was yet known for it; Queen Mary died of it, and Marlborough’s son. Epidemics, particularly of malaria, ran through whole countries; in 1657, reported Thomas Willis, almost all England was a hospital treating malarial fever. 74 Plague devastated London in 1665, killed 100,000 in Vienna in 1679, and 83,000 in Prague in 1681. 75 Occupational diseases increased with industry: Bernardino Ramazzini, professor of medicine at Padua, issued in 1700 a classic treatise, De morbis arttficum, on the damage done to painters by the chemicals in their paint, to workers in colored glass from antimony, to masons and miners from tuberculosis, to potters from vertigo, to printers from eye troubles, to physicians from the mercury they applied.
Amid ignorance and poverty the science of medicine slowly advanced. The thirst for money hampered the profession; some doctors who had made successful cures refused to reveal to other doctors the treatment they had used. 76 The medical members of the Royal Society rose above this greed, and zealously shared their discoveries with their fellows. There were now good medical schools, led by those at Leiden, Bologna, and Montpellier; and generally a degree from a recognized institution was required for the legal practice of medicine in Western Europe. The teachers of the art continued their division into two schools of treatment. Borelli defended “iatrophysical” therapy, proposing to deal with diseases as derangements of the body’s mechanism. Sylvius, developing the arguments of Paracelsus and Helmont, advocated the “iatrochemical” method of using drugs to counteract disturbances in the “humours” of the body; most of these, he thought, were due to hyperacidity. More fruitful than these general theories were discoveries in the causes of specific diseases; so Sylvius first described tubercles in the lungs, and related these morbid growths to consumption.
One of the most basic discoveries of this age was the work of that remarkable Jesuit, Athanasius Kircher of Fulda, mathematician, physicist, Orientalist, musician, and physician, and apparently the first to use the microscope in investigating disease. 77 W
ith this aid he found that the blood of plague victims contained numberless “worms” invisible to the naked eye. He saw similar animalcules in putrefying matter, and ascribed putrefaction and many diseases to their activity. He reported his findings in Scrutinium pestis (Rome, 1658), which first stated in explicit terms what Fracastoro had only suggested in 1546—the doctrine that the transfer of noxious organisms from one person or animal to another is the cause of infectious disease. 78
Medical treatment lagged behind medical research, for those who excelled in research tended to form a class distinct from those who practiced, and their communication was imperfect. Some medieval cures were still prescribed. Aubrey records an untimely success: “A woman . . . endeavored to poison her husband (who was a dropsical man) by boiling a toad in his potage; which cured him; and this was the occasion of finding out the medicine.” 79 Some new drugs entered the pharmacopoeia in the second half of the seventeenth century: ipecacuanha, cascara, peppermint . . . Dutch physicians, favoring Dutch commerce, prescribed tea as almost a panacea. 80
Two Dutchmen were the greatest medical teachers of the age: Sylvius and Boerhaave, both at Leiden. Hermann Boerhaave taught chemistry, physics, and botany as well; students came to him from all northern Europe; and he raised the status of clinical medicine by taking his maturer pupils with him on his daily rounds of the hospital beds, instructing them by direct observation and specific treatment of each individual case. His works were translated into all major European languages, even Turkish; his reputation reached to China itself.
In England clinical medicine had its finest exponent in Thomas Sydenham. After two stays at Oxford, separated by terms of service in the army, he settled in London as a general practitioner. With little theory and much experience, he came to his philosophy of disease, which he defined as “an effort of nature striving with all her might to restore the health of the patient by eliminating morbid matter.” 81 He distinguished “essential” symptoms as those caused by the foreign substance, and “accidental” as those caused by the body’s resistance to it; so fever is not an illness but a device of the organism in its self-defense. The problem of the physician is to help this process of defense. Hence Sydenham praised Hippocrates because the “Father of Medicine”