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 1699Orang-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’sCreative Evolution (1906). The debate will go on until the part understands the whole.