An Epitome of the History of Medicine

by Roswell Park

The intermediary system and bond of union between the arteries and veins, so very essential, yet up to this time unknown, was discovered by the great Malpighi, who was born in 1628 near Bologna, became professor in its university, and discovered in the lungs and mesentery of frogs, in 1661, the capillary circulation. He first described the corpuscles of the blood in 1665; he also discovered the lung-cells, as well as the cutaneous glands, certain portions of the kidney, and the pigmentary layer of the skin, named after him (rete Malpighi), which later furnished the first explanation of the difference of color in different races.

In 1690 Leuwenhoek (1632-1723), who had been making observations on the larvæ of frogs and other small animals, was able to see with his improved microscope the movements of the blood in the small vessels, and gave the important testimony of his observations. In 1687 Cowper saw the passage of the arterial into the venous current in the mesentery of a cat. The capillary connection between the two vascular systems was first demonstrated by Marchetti, but was best shown by Ruysch (1638-1731), professor at Amsterdam, the famous inventor of minute injections, who greatly advanced anatomy by the formation of collections, one of which was brought into Russia by Peter the Great at an expense of about seventy-five thousand dollars. The Russian transporters of the collection, however, drank the alcohol in which many of the preparations were preserved, and a portion of the specimens was thus ruined.

Further illustration and amplification of Harvey's views came from various sources; the last, perhaps, from Nich-olaus Steno (1638-1686), who was first a professor in Copenhagen, then a bishop and peripatetic converter of heretics. Steno first proved the heart to be a muscle that contracts actively and expels the blood. The duct that bears his name was discovered during his residence in Leyden or at Amsterdam. His name is written also "Stenson."

While ancient anatomists were able to describe in a general way the form of the lungs, their location, consistency, the ring-like structure of the trachea, and the first division of the bronchi, they did not go farther, but blindly accepted the prevalent theory that the bronchial tubes anastomosed with the terminal pulmonary veins, and that in this way atmospheric fluid was conveyed from the respiratory organs into the heart. On such vague and erroneous data was constructed the theory that the air was drawn into the lungs by the heat of the heart, which was the reservoir of the vital spirits; that in penetrating through the smaller tubes it was rarefied, its thinnest part passing into the heart, where it served as material for the formation of the vital spirit, its grosser part being exhaled. In other words, respiration was supposed to have two purposes one to refresh the lungs, which, being porous and inflammable, would otherwise take fire from the heart, or focus of animal heat; the other to furnish the pneuma, or ether, which was employed by the heart in the formation of animal spirits. Harvey's discovery upset all this, in great measure.

Next it was shown that pulmonary veins carried nothing to the heart except blood. And now, during this Reform Period, the purpose of the movements of the chest was better studied, for Borelli, Helvetius, and Haller made many experiments, as the result of which it was determined that during inspiration the thorax is enlarged in all directions, and during expiration partly collapsed by relaxation of muscles, and that there never is any empty space between the lungs and the sides of the chest; further, that air is drawn into the chest by the tendency of all gases or fluids to maintain an equilibrium, or, in other words, because Nature abhors a vacuum. This being settled, various pneumatic theories were adopted and abandoned, all of which had subsequently to give way before a knowledge of what really occurs. The truth was conceived of by Mayow in 1668. It had been noticed that blood which appeared black in issuing from the veins, became red in contact with the air, and direct observation proved a similar change of color to take place during its passage from the pulmonary veins during life. Goodwin, opening the thorax of a frog, was the first to see this, and Hessenfratz filled a silk bladder with venous blood, and, plunging it into an atmosphere of oxygen, saw the blood change from black to red. In this way and by the later labors of Bichat and Lavoisier were clearly established the mechanism and the purpose of the function of respiration.

The discovery of the lymphatic vessels and their purpose was scarcely less remarkable than that of the circulation, though marked by less eclat because it was not the work of one man, but a matter of slow development. Herophilus and Erasistratus had seen white vessels connected with the lymph-nodes in the mesentery of animals, and supposed them to be arteries full of air. Galen disputed this, for he believed that the intestinal chyle was carried by the veins of the mesentery into the liver. In 1563 Eustachius described the thoracic duct in the horse. In 1622 Aselli, Professor of Anatomy at Milan, discovered the lacteal vessels in a dog which had been killed immediately after partaking of food; having pricked one of these by mistake, he saw a white fluid issue from it. Repeating the experiment, he became certain that the white threads were vessels which drew the chyle from the intestines. He observed the valves with which they are supplied, and supposed these vessels all met in the pancreas and continued on into the liver. In 1647 Pecquet, while still a student at Montpellier, discovered the lymph-reservoir, or receptaculum chyli, and the canal which leads from it (the thoracic duct), which he followed to its termination in the left subclavian vein. Having ligated the duct, he saw it swell below and become empty above the ligature. He studied the courses of the lacteals, and convinced himself that they all entered into the common reservoir. This discovery gave the last blow to the ancient theory which attributed to the liver the function of blood-making, and confirmed the doctrine of Harvey. Strangely enough, the latter united with Riolan in opposing the discovery of Pecquet and denying its significance. From this time the lymphatic vessels and glands became objects of common interest and were investigated by many anatomists,—by Bartholin, Ruysch, the Hunters, Hewson, and, above all, by Mascagni, who was the first to give a graphic description of the whole lymphatic apparatus.

The ancients confounded, under the name "neuron," nerves, tendons, ligaments, and membranes; even Aristotle regarded the brain as an inert mass devoid of sensation, and supposed the nerves to originate in the heart. Rufus, of Ephesus, remarked that Herophilus distinguished three sorts of nerves,—the first serving for sensation and motion and proceeding from the brain and spinal marrow, the second and third serving to unite bones and muscles.

Galen also shared in this error, but, nevertheless, described the brain-membranes and the difference between white and gray matter; he supposed the cerebrum to be the seat of the soul and origin of sensory nerves, and that the cerebellum gave rise to nerves of motion; the pulsation of the cerebrum exposed was held to be a sort of brain respiration. Galen came very near recognizing the distinction between nerves and tendons, but nevertheless confused them. The anatomists of the sixteenth century described certain portions of the nervous system with, more exactness than did Galen, but not with such positiveness as to prevent Cesalpinus from renewing the Aristotelian theory that the heart was the origin of sensation and the seat of the soul. Nearly two centuries later Baglivi advanced a theory which referred vital movement to the heart and the dura mater.

The progress which accrued to comparative anatomy and physiology, and the experiments which were made on animals, during this period, shed a great deal of light upon the nervous system. The researches of Vieussens, Haller, Meckel, Vicq d'Azyr, Scarpa, Soemmering, and others had already rendered it manifest that the brain was the organ of sensation and voluntary motion, and Bichat had proposed to divide the nervous system into cerebrospinal and sympathetic branches.

Now, too, Kepler discovered that the crystalline lens was not the seat of vision, as had been supposed, but that its function, like that of other lenses, is the refraction of light. He observed that the image of objects is depicted upon the retina, and (with Schemer) demonstrated that the expansion of the optic nerve in the retina is the essential part in the organ of sight. Obviously, also, interest in the anatomy of the eye, which these observations everywhere stimulated, was, in a great measure, aided by the researches of Newton on light and color.