Part 20

§ 5. The Revival of Physiology.

The first to apply Galilean principles of measurement to biological matters was Sanctorius (1561-1636), a professor at Padua. He described a thermometer for use in taking the temperature of the human body (Figs. 39 and 40), and an apparatus for comparing the rate of pulse beats (Fig. 41). Both these he modified from devices suggested by Galileo (Fig. 38). It is an indication of the transitional character of the Science of the time that he describes these instruments in a commentary on a medieval translation of the Canon of Avicenna (p. 67). He also sought to compare the weight of the body at different times and in different circumstances. In the process of doing this, he demonstrated that the body loses weight by mere exposure, a process which he ascribed to ‘insensible perspiration’ (Fig. 37). By these experiments he laid the foundation of the modern study of ‘Metabolism’ (p. 220).

FIG. 38. The principle of Galileo’s thermometer. A tube ending in a bulb A is inverted over a mercury bath B. If the temperature fall the air in A will contract and mercury be drawn up into the tube. If the temperature rise the air in A will expand and mercury be driven out of the tube. The height of the mercury can be read on the scale SS. The reading will not be accurate because the instrument is, in fact, also a barometer, since the mercury in B is exposed to the atmospheric pressure, which will therefore affect the rise in the tube.

FIG. 39. The application of the same system by Sanctorius who used a curved tube.

FIG. 40 is not, as might be thought, a man trying to swallow a centipede, but the adaptation of the instrument of Sanctorius as a clinical thermometer.

FIG. 41. Galileo’s simple and effective ‘pulsimeter’. It consists only of a weight suspended on a thread. This thread is held in the hand and the weight made to oscillate as a pendulum. As the thread is shortened the oscillations increase in frequency. The process is continued until the pendulum oscillates to time with the pulse. The length of the free thread is then read off on the accompanying scale. It was used by Sanctorius.

While Sanctorius was engaged in this pioneer work at Padua, the movement that Vesalius had inaugurated there was making further conquests in the purely biological line. Vesalius had been succeeded at Padua by a series of anatomists of great eminence. Perhaps the most prominent among these was Jerome Fabricius (1537-1619), usually called ‘of Aquapendente’, after the small Tuscan village where he was born. This Fabricius of Aquapendente taught at Padua for over fifty years, from 1565 till his death at eighty-two in 1619. He made many contributions to the advancement of anatomy, most of which had physiological bearings. Thus, he was the effective founder of modern embryology and the author of the first illustrated work on that subject, in which he describes the formation of the chick in the egg. He was the first to give accurate figures of the structure of the eye. He developed the mechanics of muscular motion. He added to his qualities as an observer the power of attracting younger men.

In spite of all his powers, however, Fabricius never shook himself free from ancient views, and especially he was steeped in the theories of Aristotle and Galen. This backward-looking habit prevented his work from being as important as it might otherwise have been. In connection with the circulation, for instance, he made a striking discovery, but wholly failed to draw out its most important lesson.

FIG. 42. DISSECTION OF A VEIN in the thigh and leg from a work On the Valves of the Veins, published by Fabricius in 1603 at Padua. These valves prevent the passage of the blood in any direction except toward the heart. They may be seen at the points P, Q, R, S, and T.

In 1600 he published his book, On the Valves of the Veins. In it he says that these structures are so placed that their mouths are always directed toward the heart (Fig. 42), yet he never gets an inkling that the effect of these valves must be to prevent blood flowing into the veins except toward the heart. He is too set on the old Galenic physiology to permit such a revolutionary thought. The real importance of Fabricius is, therefore, not so much as an investigator but rather as a teacher, a capacity in which he shone above all other physiologists for generations to come. He would deserve our remembrance if only as the master of the discoverer of the circulation of the blood, William Harvey.

The Englishman, William Harvey (1578-1657), after education at Cambridge, went to Padua in 1599, when Fabricius was at the height of his powers. Returning to England in 1602, he set up in practice in London. During the years which followed, he was dissecting and experimenting very industriously, and by 1615 had reached a clear conception of the circulation of the blood (Fig. 43), though he did not publish his discovery till some thirteen years later.

To discuss the actual steps by which Harvey made his discovery would be beyond our scope. He had, however, been well trained in experimenting on living animals by Fabricius, and had read widely in anatomical literature. He was of a contemplative turn of mind and his quiet and cautious temper, united with his enthusiasm and skill as an experimenter, provided a superb mental equipment for a life of scientific investigation.

Harvey, early in his work, reached two fundamental conceptions concerning the vascular system. He perceived that the valves in the veins would permit the blood to pass only towards the heart (Fig. 43), while those in the great arteries arising from the heart would permit the blood to pass only away from the heart. In connection with the movement of the blood, Harvey’s crucial point is that it must be continuous, and always in one direction. This really clinches the matter, for consider the capacity of the heart. Let us suppose that either ventricle holds but 2 ounces of blood. The pulse beats 72 times a minute and 72 × 60 times an hour. In the course of one hour, therefore, the left ventricle will throw into the aorta, or the right ventricle into the pulmonary artery, no less than 72 × 60 × 2 = 8,640 ounces = 38 stones 8 lb. In other words, in one hour the ventricle will throw into the great artery more than three times the body weight of a heavy man. Where can all this blood come from? Whither can it all go? It cannot come from the ingested food and drink, for no one could consume so much in one hour! It cannot reach and remain in the tissues, for they would soon all burst and ooze with blood! The solution of the puzzle, Harvey came to see, is that it is the same blood that is always being pumped into the arteries, and the same blood that is always coming back through the veins. In other words the blood circulates, a fact which Harvey proceeded to demonstrate with convincing thoroughness (Fig. 43).

FIG. 43. DIAGRAM TO ILLUSTRATE THE NATURE OF THE CIRCULATION OF THE BLOOD. Leaving the left ventricle, when the walls of that cavity contract, the blood is forced through the valves into the great artery known as the aorta. From the aorta it passes into smaller and ever smaller arteries, finally reaching the systemic capillaries or the portal capillaries. After travelling through one or other capillary network it enters a vein. Thence it passes into larger and ever larger veins, until it ultimately enters the great vein known as the vena cava that opens into the right auricle. It has now completed the Greater Circulation. As the right auricle contracts the blood passes through the valves between the right auricle and right ventricle into the right ventricle. From there it enters the Lesser Circulation, passing into the great pulmonary artery, which conducts it to the lung. In the lung the pulmonary artery breaks up into branches and finally into capillaries. Through these the blood travels until it reaches a tributary of the pulmonary vein and finally the pulmonary vein itself. The pulmonary vein empties its blood into the left auricle. From the left auricle the blood passes at last into the left ventricle from which it started, having traversed both the Greater and the Lesser Circulations.

To understand the change which Harvey wrought in the conception of the workings of the body, this description and diagram should be compared with the description and diagram on pages 56-59.

We may note that, though Harvey demonstrated the existence of the circulation, he was never able to follow it throughout, for he did not see the capillary vessels by which the blood is conveyed from the terminal branches of the arteries to the smallest tributaries of the veins. These were first demonstrated by Malpighi (p. 116).

The knowledge of the circulation of the blood has been the basis of the whole of modern Physiology and with it of the whole of modern rational Medicine. The attitude of Galen and Aristotle towards the heart and the great vessels passed into the shadow. The blood, it was seen, is a carrier always going round and round on the same beat. What it carries, and why, how and where it takes up its loads, and how, where, and why it parts with them, these are questions the answering of which has been the main task of Physiology in the centuries that have followed. As each of the questions has obtained a more and more rational answer, so clinical Medicine has always made a step forward, and has come to approach more nearly to a true science. Thus it is that the work of Harvey lies at the back of almost every important medical advance.

FIG. 44. THE VALVES in the superficial veins as seen in the bandaged arms of living men, from William Harvey’s great work on the Circulation of the Blood, printed in 1628. The bandage is seen on the upper arm in each case, and the valves are indicated, as in life, by nodes or swellings in the veins. If a finger is pressed along the vein from one valve to another as from node O to node H in a direction away from the heart, the vein from O to H will be emptied of blood. It will remain empty, since the valve at O does not permit the passage of blood away from the heart, but only towards it. This observation was Harvey’s starting point for his great discovery.

§ 6. Microscopic Analysis of the Animal Body.

The compound microscope was first made into an effective instrument by Galileo. It was, as it were, a by-product of his invention of the telescope. With that instrument he had seen enough to convince himself that the movement of the Sun round the Earth was but an appearance. At the very time that Harvey was giving his first course of lectures securely in London, Galileo’s teaching was attracting the unwelcome attention of the Inquisition in Rome.

Galileo’s microscopes, however, were far less satisfactory than his telescopes. For optical reasons which we need not discuss, these early compound microscopes failed to give a clear picture. With any high degree of magnification, the image was always blurred and distorted. More than three centuries were to pass before a better compound system was introduced. But about 1650 a way was found of constructing and mounting simple lenses of very high power. Many of the most important microscopical discoveries of the second half of the seventeenth century were, therefore, made with a simple lens. This was notably the case with much of the work of the great investigators Malpighi and Leeuwenhoek (Fig. 49 A).

FIG. 45. LUNGS OF FROG, showing the capillary vessels from a figure by Malpighi in the rare first edition of his work On the Lungs, published at Bologna in 1661. A is the part of the larynx, B is the opening of the larynx into the trachea or air-tube leading to the lung. The letters EEE represent the outer surface of the lung and exhibit the network of capillary vessels. On the other side the sack-like lung has been laid open, and is viewed from the inside. The letters HHH are placed upon veins on the inner surface of the lung. These arise from capillaries which are indicated between the veins.

Marcello Malpighi (1628-94) was born in the year in which Harvey’s work was published. He became a professor at Bologna, having early developed great skill in minute investigation. His first work, which appeared in 1661, supplied the element missing in the investigations of Harvey, for he describes the actual passage of blood from the arteries to the veins through the ‘capillary’ blood-vessels (Fig. 45). Harvey, who did not use a microscope, knew nothing of the capillaries. The object which yielded up the secret was the lung of the frog. This organ in the frog happens to be almost transparent, is very simple in structure, and is furnished on its surface with particularly conspicuous capillary vessels. Malpighi could hardly have selected an object better suited for this particular research. This important discovery of his drew the attention of scientific men in England. The Royal Society soon entered into correspondence with him, and during the remainder of his life undertook the publication of his researches.

FIG. 46 is the whole embryonic area, at about the end of the second day of incubation. The embryo itself is seen with its large head containing the three ‘cerebral vesicles’ (which are the rudiments of the brain), the large eye, the protuberant coiled heart (NM), from which vessels pass to the ‘vascular area’. The segmented vertebral column is well seen, as well as the vessels forming a network as they meander over the vascular area.

FIG. 47 exhibits the embryo more enlarged and in greater detail.

FIG. 48 is an enlarged figure of the heart; the part D will ultimately form the ventricle, B the auricle, and A the vena cava. At F the aorta sends forth three branches which unite again. The nature of these branches was not understood in Malpighi’s time. They have been explained in modern times by embryologists working under the inspiration of evolutionary theory as having once furnished the blood-supply to the gills of a fish-like ancestor.

FIG. 49 is a part of the segmented vertebral column still more enlarged.

FIG. 49A. ONE OF LEEUWENHOEK’S MICROSCOPES. To understand the figure turn the book at right angles to the line of print. The object to be examined--here the tail of a small eel--is placed in water in the test-tube B. This test-tube is held firmly by two springs in the frame A. The microscope itself is simply a flat metal plate D, into which is let a very minute lens, the setting of which is shown above the letter D (when the head of the eel is downwards). The lens is focused by means of a fine screw which moves the whole plate.