Part 21

The contributions of Malpighi to biological knowledge were very numerous and important. The study of early development, embryology as it is now called, was greatly extended by him. The later stages of embryological development had been investigated by Fabricius (p. 110) and some additions to the subject had been made by Harvey. Malpighi, applying his microscope to the earlier germ of the animal body, described in detail the development of the organs, notably of the heart and the nervous system (Figs. 46-49). He also demonstrated the minute structure of the skin, spleen and liver, in all of which there are anatomical structures that still bear his name. He investigated microscopically the structure and physiology of insects and plants, and his figures of the cell-walls of the latter are good and clear.

FIG. 50. Oval blood corpuscles of salmon showing nuclei.

FIG. 51. Human red blood corpuscles.

FIG. 52. Drawing of human red blood corpuscles for comparison with Leeuwenhoek’s figures.

FIG. 53. Capillary network in web of frog’s foot. A, C and E are arterioles, B, D and F are venules.

A most remarkable contemporary microscopist was the Dutchman, Anthony van Leeuwenhoek (1632-1723). Without medical or scientific training, desultory and secretive in his mode of working, he was withal an observer of genius and a very shrewd investigator. During his long and industrious life he made a series of disconnected discoveries which for originality and importance have been surpassed by no other microscopic observer. He improved and extended the knowledge of the capillary circulation of which Malpighi was the discoverer (Fig. 53), he gave figures of the blood corpuscles (Figs. 50-1), of spermatozoa and of fibres of muscles (Figs. 55-56a), and advanced the knowledge of embryology. He always worked with a simple microscope, using lenses of exceedingly short focal length (Fig. 49A). It is astounding that, with such an instrument, he saw and figured bacteria as early as 1683 (Fig. 54).

FIG. 54. THE FIRST REPRESENTATION OF BACTERIA. They were figured by Leeuwenhoek in the Philosophical Transactions of the Royal Society of London in 1683.

FIG. 55 shows a muscle teased up into bundles of fibres, magnified.

FIG. 56 is a more magnified view of a bundle of fibres. The cut fibres are shown at the end.

FIG. 56A is a very highly magnified view of a single fibre showing very clearly the striations that are very characteristic of voluntary muscle.

The short life of a second Dutch microscopist of the seventeenth century, Jan Jacobz Swammerdam (1637-80), was abbreviated yet further, as regards scientific achievement, by his insanity. In his brief working period he produced his Bible of Nature which, alone of the scientific writings of his age, is still consulted by modern naturalists for the unique beauty and accuracy of its figures. He extended the knowledge of embryology and he made a series of physiological experiments which involved the very modern physiological device known as the ‘nerve-muscle preparation’. He is thus the founder of an important department of Physiology. Swammerdam showed that, during contraction, a muscle does not increase in bulk, and that therefore the nerve brings nothing to it in the way of the hypothetical ‘nervous fluid’ in which many then believed (Fig. 63). He applied the same reasoning to the heart (Figs. 57-60). Swammerdam was perhaps the first to see the blood corpuscles. Like several of his contemporaries and followers, he made injection preparations of much beauty and delicacy. His great work was not published till after his death. The copper plates that he had prepared for it were found and purchased by Boerhaave (p. 140), who produced them at his own expense.

These microscopists and several others in the seventeenth century did much to explore the minute structure of the animal body. Their revelations showed at once an unexpected complexity of all the parts, and an unexpected resemblance of some of those parts which appear diverse to the naked eye. Thus, the structure of the body came to be subjected to a process that we may call ‘microscopic analysis’. For long after the time of these classical microscopists no effective improvements were made in the microscope, and the progress of microscopic analysis lay almost dormant. With the improvements in the microscope of the nineteenth century, the method was taken up again with triumphant results.

FIG. 57 is the simplest form of what physiologists call a ‘nerve-muscle preparation’. It is merely a living muscle dissected away from the body, but with its nerve still attached. In the experiment the two tendons of the muscle are held by the two hands. An assistant pinches the nerve with forceps. The muscle thereon contracts and draws the two hands together.

FIG. 58 shows the muscle passed through a glass tube. Its two tendons are fastened by two pins. When the nerve is pinched the pins are drawn towards each other, and the muscle, in contracting, fills the middle of the tube.

FIG. 59 shows the nerve-muscle preparation enclosed within a tube. This tube has a narrow neck in which, at e, is a drop of water. The other end of the tube is closed by a cork. The nerve may be squeezed by pulling the thread c c, which passes through the cork and drags the nerve into a narrow wire loop.

FIG. 60 is a similar experiment with the heart, which contracts and expands spontaneously and needs no irritation.

The experiments 59 and 60 show that during ‘contraction’ no new substance passes into the muscle, since it does not then increase in size. This gives the death-blow to the conception of a ‘nervous fluid’ passing into the muscle to cause contraction by distending it.

§ 7. From Alchemy to Chemistry.

During the sixteenth and the first part of the seventeenth century the basic science of Mechanics had been placed on a firm footing by Galileo. Astronomy, with Galileo and Kepler, had made the great break with the past. Anatomy and Physiology had put on their modern dress. Chemical knowledge, however, remained peculiarly backward. Many advances, it is true, had been made in technical processes, but investigations designed to throw light on theory were mostly prosecuted by the band of dupes and charlatans who, since the Middle Ages, had been seeking the Philosopher’s Stone. The old theory of the four elements, earth, air, fire, and water (p. 34), formed an ill basis for experiment. Some philosophers, it is true, had put forward crude atomic theories, but they had little experimental evidence to adduce. Nevertheless even the alchemists had made some advance and had, for instance, perfected a system of weighing.

The great defect of the ancient view of matter was that it contained no definite conception of the nature of a pure substance. Metals, for instance, were regarded, like other substances, as a mixture in certain proportions of the four elements of Aristotle (p. 34). Thus, the transmutation of one metal or one substance into another by distillation did not seem an absurdity, or even a task of special theoretical difficulty.

The main agent in changing the chemical outlook was Robert Boyle (1627-91). He was a member of a small association of scientific men, the Invisible College, which met first in London, then in Oxford, and finally in 1663 was incorporated by Royal Charter as the Royal Society. These men were satisfied that the only way to learn anything effective about Nature was by observation and experiment. From their discussions all purely speculative views were excluded. They agreed to meet together solely to compare experiences, to demonstrate experiments, and to draw immediate deductions. None of them was more active in these matters than Boyle.

The actual chemical and physical discoveries of Boyle were very numerous, but his great achievement, the real service he rendered to learning in general and to medicine in particular, was his introduction of a new spirit into Chemistry. Under him that study was no longer prosecuted for purely practical ends; it was set free from the mystic factor in Alchemy and it was loosed from the chains which bound it to Medicine, to the disadvantage of both. Chemistry thus became an independent science, the principles of which were to be ascertained by experiment, and its truths pursued for their own sake.

Boyle demonstrated that the air is a material substance and has weight. By means of his air-pump, he proved clearly that this substance is necessary for the support of respiration (Fig. 63). The law of the compressibility of gases is still known by his name. Most important of all Boyle’s contributions to chemical theory was his adumbration of the conception of a chemical element in our modern sense, and his view, which he borrowed from another philosopher, of the atomic structure of matter.

Under the inspiration of Boyle and his colleagues, chemical works of the second half of the seventeenth century exhibit in general a positive, cautious, experimental spirit, and show a great contrast to the mystical and obscure writings of the first half of the century, which have much affinity with Alchemy. A fine exponent of this new spirit was John Mayow (1645-79), who was prevented by an early death from fulfilling all his promise. He was the first to recognize clearly that there is a substance or principle in air which is concerned at once with combustion, respiration, and the conversion of venous into arterial blood. In this sense he was the discoverer of Oxygen (Figs. 74 and 75).

§ 8. The Medical Theorists.

The great advances in the physical and biological sciences, instituted during the sixteenth and seventeenth century, left the old medical theories derelict. We have already traced the wrecking of the Galenic physiology. With its destruction, the old ideas concerning the three types of spirit, natural, vital, and animal, went by the board. The doctrine of the circulation of the blood (p. 113) and the investigations of the new Chemistry accorded ill with the old humoral pathology, which ascribed all disease to excess or defect of one of the four humors, blood, phlegm, bile, and melancholy (p. 34). Numerous fresh theories arose, of which the more important can be classed under the three headings Iatrophysics, Iatrochemistry, and Vitalism.

(a) Iatrophysics.

The physical discoveries of Galileo and the demonstrations of Sanctorius (p. 108) and of Harvey (p. 111) gave a great impetus to the attempt to explain the workings of the animal body on purely mechanical grounds. The writers who took this point of view are known as the Iatrophysicists. One of the earliest and most impressive exponents of physiological theory along these lines was the French philosopher René Descartes (1596-1650). His work on the subject appeared posthumously in 1662. It is important as the first modern book entirely devoted to the subject of Physiology.