His Physiognomy.—This classic with the Latin title,De Humani Corporis Fabrica, requires some special notice; but first let us have a portrait of Vesalius, the master. Fig. 4 shows a reproduction of the portrait with which his work is provided. He is represented in academic costume, probably that which he wore at lectures, in the act of demonstrating the muscles of the arm. The picture is reduced, and in the reduction loses something of the force of the original. We see a strong, independent, self-willed countenance; what his features lack in refinement they make up in force; not an artistic or poetic face, but the face of the man of action with scholarly training.
His Great Book.—The book of Vesalius laid the foundation of modern biological science. It is more than a landmark in the progress of science—it created an epoch. It is not only interesting historically, but on account of the highly artistic plates with which it is illustrated it is interesting to examine by one not an anatomist. For executing the plates Vesalius secured the service of a fellow-countryman, John Stephen de Calcar, who was one of the most gifted pupils of Titian. The drawings are of such high artistic quality that for a long time they were ascribed to Titian. The artist has attempted to soften the necessarily prosaic nature of anatomical illustrations by introducing an artistic background of landscape of varied features, with bridges, roads, streams,buildings, etc. The employment of a background even in portrait-painting was not uncommon in the same century, as in Leonardo da Vinci's well-known Mona Lisa, with its suggestive perspective of water, rocks, etc.
Fig. 5.—Anatomical Sketch from Vesalius'sFabrica.(Photographed and reduced from the facsimile edition of 1728.)
Fig. 5 will give an idea on a small scale of one of the plates illustrating the work of Vesalius. The plates in the original are of folio size, and represent a colossal figure in the foreground, with a background showing between the limbs and at the sides of the figure. There is considerable variety as regards the background, no two plates being alike.
Also, in delineating the skeleton, the artist has given to it an artistic pose, as is shown in Fig. 6, but nevertheless the bones are well drawn. No plates of equal merit had appeared before these; in fact, they are the earliest generally known drawings in anatomy, although woodcuts representing anatomical figures were published as early as 1491 by John Ketham. Ketham's figures showed only externals and preparations for opening the body, but rude woodcuts representing internal anatomy and the human skeleton had been published notably by Magnus Hundt, 1501; Phrysen, 1518; and Berengarius, 1521 and 1523. Leonardo da Vinci and other artists had also executed anatomical drawings before the time of Vesalius.
Previous to the publication of the complete work, Vesalius, in 1538, had published six tables of anatomy, and, in 1555, he brought out a new edition of theFabrica, with slight additions, especially in reference to physiology, which will be adverted to in the chapter on Harvey.
Fig. 6.—The Skeleton, from Vesalius'sFabrica.
In the original edition of 1543 the illustrations are not collected in the form of plates, but are distributed through the text, the larger ones making full-page (folio) illustrations. In this edition also the chapters are introduced with an initial letter showing curious anatomical figures in miniature, some of which are shown in Fig. 7.
Fig. 7.—Initial letters from Vesalius'sFabricaof 1543.
TheFabricaof Vesalius was a piece of careful, honest work, the moral influence of which must not be overlooked. At any moment in the world's history, work marked by sincerity exercises a wholesome influence, but at this particular stage of intellectual development such work was an innovation, and its significance for progress was wider and deeper than it might have been under different circumstances.
Opposition to Vesalius.—The beneficent results of his efforts were to unfold afterward, since, at the time, his utterances were vigorously opposed from all sides. Not only did the ecclesiastics contend that he was disseminating false and harmful doctrine, but the medical men from whom he might have expected sympathy and support violently opposed his teachings.
Many amusing arguments were brought forward to discredit Vesalius, and to uphold the authority of Galen. Vesalius showed that in the human body the lower jaw is a single bone—that it is not divided as it is in the dog and other lower mammals, and, as Galen had taught, also in thehuman subjects. He showed that the sternum, or breast bone, has three parts instead of eight; he showed that the thigh bones are straight and not curved, as they are in the dog. Sylvius, his old teacher, was one of his bitterest opponents; he declared that the human body had undergone changes in structure since the time of Galen, and, with the object of defending the ancient anatomist, "he asserted that the straight thigh bones, which, as every one saw, were not curved in accordance with the teaching of Galen, were the result of the narrow trousers of his contemporaries, and that they must have been curved in their natural condition, when uninterfered with by art!"
The theologians also found other points for contention. It was a widely accepted dogma that man should have one less rib on one side, because from the Scriptural account Eve was formed from one of Adam's ribs. This, of course, Vesalius did not find to be the case. It was also generally believed at this time that there was in the body an indestructible resurrection-bone which formed the nucleus of the resurrection-body. Vesalius said that he would leave the question of the existence of such a bone to be decided by the theologians, as it did not appear to him to be an anatomical question.
The Court Physician.—The hand of the church was heavy upon him, and the hatred shown in attacks from various quarters threw Vesalius into a state of despondency and anger. In this frame of mind he destroyed manuscripts upon which he had expended much labor. His disappointment in the reception of his work probably had much to do in deciding him to relinquish his professorship and accept the post of court physician to Charles V of the United Kingdoms of Spain and Belgium. After the death of Charles, he remained with Philip II, who succeeded to the throne. Here he waxed rich and famous, but he was always under suspicion by the clerical powers, who from time to time found means of discrediting him. The circumstances of his leaving Spain are not definitely known. One account has it that he made apost-mortemexamination of a body which showed signs of life during the operation, and that he was required to undertake a pilgrimage to the Holy Land to clear his soul of sacrilege. Whether or not this was the reason is uncertain, but after nineteen years at the Spanish Court he left, in 1563, and journeyed to Jerusalem. On his return from Palestine he suffered shipwreck and died from the effects of exposure on Zanti, one of the Ionian Islands. It is also said that while on this pilgrimage he had been offered the position of professor of anatomy as successor to Fallopius, who had died in 1563, and that, had he lived, he would have come back honorably to his old post.
Eustachius and Fallopius.—The work of two of his contemporaries, Eustachius and Fallopius, requires notice. Cuvier says in hisHistoire des Sciences Naturellesthat those three men were the founders of modern anatomy. Vesalius was a greater man than either of the other two, and his influence was more far-reaching. He reformed the entire field of anatomy, while the names of Eustachius and Fallopius are connected especially with a smaller part of the field. Eustachius described the Eustachian tube of the ear and gave especial attention to sense organs; Fallopius made special investigations upon the viscera, and described the Fallopian tube.
Fallopius was a suave, polite man, who became professor of anatomy at Padua; he opposed Vesalius, but his attacks were couched in respectful terms.
Eustachius, the professor of anatomy at Rome, was of a different type, a harsh, violent man, who assailed Vesalius with virulence. He corrected some mistakes of Vesalius, and prepared new plates on anatomy, which, however, werenot published until 1754, and therefore did not exert the influence upon anatomical studies that those of Vesalius did.
Fig. 8.—Fallopius, 1523-1563.
The Especial Service of Vesalius.—It should be remembered that both these men had the advantage of the sketches made under the direction of Vesalius. Pioneers and path-breakers are under special limitations of being in a new territory, and make more errors than they would in following another's survey of the same territory; it takes much less creative force to correct the errors of a first survey than to make the original discoveries. Everything considered, Vesalius is deserving of the position assigned to him. He was great in a larger sense, and it was his researches in particular which re-established scientific method and made further progress possible. His errors were corrected, not byan appeal to authority, but by the method which he founded. His great claim to renown is, not that his work outshone all other work (that of Galen in particular) in accuracy and brilliancy, but that he overthrew dependence on authority and re-established the scientific method of ascertaining truth. It was the method of Aristotle and Galen given anew to the world.
The spirit of progress was now released from bondage, but we have still a long way to go under its guidance to reach the gateway of modern biology.
CHAPTER III
WILLIAM HARVEY AND EXPERIMENTAL OBSERVATION
Afterthe splendid observations of Vesalius, revealing in a new light the construction of the human body, Harvey took the next general step by introducing experiment to determine the use or purpose of the structures that Vesalius had so clearly exposed. Thus the work of Harvey was complemental to that of Vesalius, and we may safely say that, taken together, the work of these two men laid the foundations of the modern method of investigating nature. The results they obtained, and the influence of their method, are of especial interest to us in the present connection, inasmuch as they stand at the beginning of biological science after the Renaissance. Although the observations of both were applied mainly to the human body, they served to open the entire field of structural studies and of experimental observations on living organisms.
Many of the experiments of Harvey, notably those relating to the movements of the heart, were, of course, conducted upon the lower animals, as the frog, the dog, etc. His experiments on the living human body consisted mainly in applying ligatures to the arms and the legs. Nevertheless, the results of all his experiments related to the phenomena of the circulation in the human body, and were primarily for the use of medical men.
In what sense the observations of the two men were complemental will be better understood when we remember that there are two aspects in which living organisms should always be considered in biological studies; first, the structure, and, then, the use that the structures subserve. One view is essential to the other, and no investigation of animals and plants is complete in which the two ideas are not involved. Just as a knowledge of the construction of a machine is necessary to understand its action, so the anatomical analysis of an organ must precede a knowledge of its office. The term "physiological anatomy of an organ," so commonly used in text-books on physiology, illustrates the point. We can not appreciate the work of such an organ as the liver without a knowledge of the arrangement of its working units. The work of the anatomist concerns the statics of the body, that of the physiologist the dynamics; properly combined, they give a complete picture of the living organism.
It is to be remembered that the observations of Vesalius were not confined exclusively to structure; he made some experiments and some comments on the use of parts of the body, but his work was mainly structural, while that which distinguishes Harvey's research is inductions founded on experimental observation of the action of living tissues.
The service of Vesalius and Harvey in opening the path to biological advance is very conspicuous, but they were not the only pioneers; their work was a part of the general revival of science in which Galileo, Descartes, and others had their part. While the birth of the experimental method was not due to the exertions of Harvey alone, nevertheless it should stand to his credit that he established that method in biological lines. Aristotle and Galen both had employed experiments in their researches, and Harvey's step was in the nature of a revival of the method of the old Greeks.
Harvey's Education.—Harvey was fitted both by native talent and by his training for the part which he played in the intellectual awakening. He was born at Folkestone, on the south coast of England, in 1578, the son of a prosperous yeoman. The Harvey family was well esteemed, and thefather of William was at one time the mayor of Folkestone. Young Harvey, after five years in the King's school at Canterbury, went to Cambridge, and in 1593, at the age of sixteen, entered Caius College. He had already shown a fondness for observations upon the organization of animals, but it is unlikely that he was able to cultivate this at the university. There his studies consisted mainly of Latin and Greek, with some training in debate and elementary instruction in the science of physics.
At Padua.—In 1597, at the age of nineteen, he was graduated with the Arts degree, and the following year he turned his steps toward Italy in search of the best medical instruction that could be found at that time in all the world. He selected the great university of Padua as his place of sojourn, being attracted thither by the fame of some of its medical teachers. He was particularly fortunate in receiving his instruction in anatomy and physiology from Fabricius, one of the most learned and highly honored teachers in Italy. The fame of this master of medicine, who, from his birthplace, is usually given the full name of Fabriciusab Aquapendente, had spread to the intellectual centers of the world, where his work as anatomist and surgeon was especially recognized. A fast friendship sprang up between the young medical student and this ripe anatomist, the influence of which must have been very great in shaping the future work of Harvey.
Fabricius was already sixty-one years of age, and when Harvey came to Padua was perfecting his knowledge upon the valves of the veins. The young student was taken fully into his confidence, and here was laid that first familiarity with the circulatory system, the knowledge of which Harvey was destined so much to advance and amplify. But it was the stimulus of his master's friendship, rather than what he taught about the circulation, that was of assistance to Harvey. For the views of Fabricius in reference to the circulation werethose of Galen; and his conception of the use of the valves of the veins was entirely wrong. A portrait of this great teacher of Harvey is shown in Fig. 9.
At Padua young Harvey attracted notice as a student of originality and force, and seems to have been a favorite with the student body as well as with his teachers. His position in the university may be inferred from the fact that he belonged to one of the aristocratic-student organizations, and, further, that he was designated a "councilor" for England. The practice of having student councilors was then in vogue in Padua; the students comprising the council met for deliberations, and very largely managed the university by their votes upon instructors and university measures.
It is a favorable comment upon the professional education of his time that, after graduating at the University of Cambridge, he studied four or more years (Willis says five years) in scientific and medical lines to reach the degree of Doctor of Physic.
On leaving Padua, in 1602, he returned to England and took the examinations for the degree of M.D. from Cambridge, inasmuch as the medical degree from an English university advanced his prospects of receiving a position at home. He opened practice, was married in 1604, and the same year began to give public lectures on anatomy.
Fig. 9.—Fabricius, 1537-1619, Harvey's Teacher.
His Personal Qualities.—Harvey had marked individuality, and seems to have produced a powerful impression upon those with whom he came in contact as one possessing unusual intellectual powers and independence of character. He inspired confidence in people, and it is significant that, in reference to the circulation of the blood, he won to his way of thinking his associates in the medical profession. This is important testimony as to his personal force, since his ideas were opposed to the belief of the time, and since also away from home they were vigorously assailed.
Although described as choleric and hasty, he had also winning qualities, so that he retained warm friendships throughout his life, and was at all times held in high respect. It must be said also that in his replies to his critics, he showed great moderation.
Fig. 10.—William Harvey, 1578-1667.
The contemplative face of Harvey is shown in Fig. 10. This is taken from his picture in the National Portrait Gallery in London, and is usually regarded as the second-best portrait of Harvey, since the one painted by Jansen, now in possession of the Royal College of Physicians, is believed to be the best one extant. The picture reproduced here shows a countenance of composed intellectual strength, with a suggestion, in the forehead and outline of the face, of some of the portraits of Shakespeare.
An idea of his personal appearance may be had from the description of Aubrey, who says: "Harvey was not tall, but of the lowest stature; round faced, with a complexion like the wainscot; his eyes small, round, very black, and full of spirit; his hair black as a raven, but quite white twenty years before he died; rapid in his utterance, choleric, given to gesture," etc.
He was less impetuous than Vesalius, who had published his work at twenty-eight; Harvey had demonstrated his ideas of the circulation in public anatomies and lectures for twelve years before publishing them, and when his great classic on the Movement of the Heart and Blood first appeared in 1628, he was already fifty years of age. This is a good example for young investigators of to-day who, in order to secure priority of announcement, so frequently rush into print with imperfect observations as preliminary communications.
Harvey's Writings.—Harvey's publications were all great; in embryology, as in physiology, he produced a memorable treatise. But his publications do not fully represent his activity as an investigator; it is known that through the fortunes of war, while connected with the sovereign Charles I as court physician, he lost manuscripts and drawings upon the comparative anatomy and development of insects and other animals. His position in embryology will be dealt with in the chapter on the Development of Animals, and he will come up for consideration again in the chapter on the Rise of Physiology. Here we are concerned chiefly with his general influence on the development of biology.
His Great Classic on Movement of the Heart and Blood.—Since his book on the circulation of the blood is regarded as one of the greatest monuments along the highroad of biology, it is time to make mention of it in particular. Although relatively small, it has a long title out of proportion to its size:Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, which maybe freely translated, "An Anatomical Disquisition on the Movement of the Heart and Blood in Animals." The book is usually spoken of under the shorter title,De Motu Cordis et Sanguinis. The full title seems somewhat repellent, but the contents of the book will prove to be interesting to general readers. It is a clear, logical demonstration of the subject, proceeding with directness from one point to another until the culminating force of the argument grows complete and convincing.
The book in its first edition was a quarto volume of seventy-eight pages, published in Frankfort in 1628. An interesting facsimile reprint of this work, translated into English, was privately reproduced in 1894 by Dr. Moreton and published in Canterbury. As stated above, it is known that Harvey had presented and demonstrated his views in his lectures since 1616. In his book he showed for the first time ever in print, that all the blood in the body moves in a circuit, and that the beating of the heart supplies the propelling force. Both ideas were new, and in order to appreciate in what sense they were original with Harvey, we must inquire into the views of his forerunners.
Question as to Harvey's Originality.—The question of how near some of his predecessors came to anticipating his demonstration of the circulation has been much debated. It has been often maintained that Servetus and Realdus Columbus held the conception of the circulation for which Harvey has become so celebrated. Of the various accounts of the views of Harvey's predecessors, those of Willis, Huxley,and Michael Foster are among the most judicial; that of Foster, indeed, inasmuch as it contains ample quotations from the original sources, is the most nearly complete and satisfactory. The discussion is too long to enter into fully here, but a brief outline is necessary to understand what he accomplished, and to put his discovery in the proper light.
To say that he first discovered—or, more properly, demonstrated—the circulation of the blood carries the impression that he knew of the existence of capillaries connecting the arteries and the veins, and had ocular proof of the circulation through these connecting vessels. But he did not actually see the blood moving from veins to arteries, and he knew not of the capillaries. He understood clearly from his observations and experiments that all the blood passes from veins to arteries and moves in "a kind of circle"; still, he thought that it filters through the tissues in getting from one kind of vessel to the other. It was reserved for Malpighi, in 1661, and Leeuwenhoek, in 1669, to see, with the aid of lenses, the movement of the blood through the capillaries in the transparent parts of animal tissues. (See under Leeuwenhoek, p. 84.)
The demonstration by Harvey of the movement of the blood in a circuit was a matter of cogent reasoning, based on experiments with ligatures, on the exposure of the heart in animals and the analysis of its movements. It has been commonly maintained (as by Whewell) that he deduced the circulation from observations of the valves in the veins, but this is not at all the case. The central point of Harvey's reasoning is that the quantity of blood which leaves the left cavity of the heart in a given space of time makes necessary its return to the heart, since in a half-hour (or less) the heart, by successive pulsations, throws into the great artery more than the total quantity of blood in the body. Huxley pointsout that this is the first time that quantitative determinations were introduced into physiology.
Views of His Predecessors on the Movement of the Blood.—Galen's view of the movement of the blood was not completely replaced until the establishment of Harvey's view. The Greek anatomist thought that there was an ebb and flow of blood within both veins and arteries throughout the system. The left side of the heart was supposed to contain blood vitalized by a mixture of animal spirits within the lungs. The veins were thought to contain crude blood. He supposed, further, that there was a communication between the right and the left side of the heart through very minute pores in the septum, and that some blood from the right side passed through the pores into the left side and there became charged with animal spirits. It should also be pointed out that Galen believed in the transference of some blood through the lungs from the right to the left side of the heart, and in this foreshadowed the views which were later developed by Servetus and Realdus Columbus.
Fig. 11.—Scheme of the Portal Circulation According to Vesalius, 1543.
Vesalius, in the first edition of his work (1543) expressed doubts upon the existence of pores in the partition-wall of the heart through which blood could pass; and in the second edition (1555) of theFabricahe became more skeptical. In taking this position he attacked a fundamental part of the belief of Galen. The careful structural studies of Vesalius must have led him very near to an understanding of the connection between arteries and veins. Fig. 11 shows one of his sketches of the arrangement of arteries and veins. He saw that the minute terminals of arteries and veins came very close together in the tissues of the body, but he did not grasp the meaning of the observation, because his physiology was still that of Galen; Vesalius continued to believe that the arteries contained blood mixed with spirits, and the veins crude blood, and his idea of the movement was that of anebb and flow. In reference to the anatomy of the blood-vessels, he goes so far as to say of the portal vein and the vena cava in the liver that "the extreme ramifications of these veins inosculate with each other, and in many places appear to unite and be continuous." All who followed him had the advantage of his drawings showing the parallel arrangement of arteries and veins, and their close approach to each other in their minute terminal twigs, but no one before Harveyfully grasped the idea of the movement of the blood in a complete circuit.
Servetus, in his work on the Restoration of Christianity (Restitutio Christianismi, 1553), the work for which Calvin accomplished his burning at the stake, expressed more clearly than Galen had done the idea of a circuit of blood through the lungs. According to his view, some of the blood took this course, while he still admits that a part may exude through the wall of the ventricle from the right to the left side. This, however, was embodied in a theological treatise, and had little direct influence in bringing about an altered view of the circulation. Nevertheless, there is some reason to think that it may have been the original source of the ideas of the anatomist Columbus, as the studies into the character of that observer by Michael Foster seem to indicate.
Realdus Columbus, professor of anatomy at Rome, expressed a conception almost identical with that of Servetus, and as this was in an important work on anatomy, published in 1559, and well known to the medical men of the period, it lay in the direct line of anatomical thought and had greater influence. Foster suggests that the devious methods of Columbus, and his unblushing theft of intellectual property from other sources, give ground for the suspicion that he had appropriated this idea from Servetus without acknowledgment. Although Calvin supposed that the complete edition of a thousand copies of the work of Servetus had been burned with its author in 1553, a few copies escaped, and possibly one of these had been examined by Columbus. This assumption is strengthened by the circumstance that Columbus gives no record of observations, but almost exactly repeats the words of Servetus.
Cæsalpinus, the botanist and medical man, expressed in 1571 and 1593 similar ideas of the movement of the blood (probably as a matter of argument, since there is no recordof either observations or experiments by him). He also laid hold of a still more important conception, viz., that some of the blood passes from the left side of the heart through the arteries of the body, and returns to the right side of the heart by the veins. But a fair consideration of the claims of these men as forerunners of Harvey requires quotations from their works and a critical examination of the evidence thus adduced. This has been excellently done by Michael Foster in hisLectures on the History of Physiology. Further considerations of this aspect of the question would lie beyond the purposes of this book.
At most, before Harvey, the circuit through the lungs had been vaguely defined by Galen, Servetus, Columbus, and Cæsalpinus, and the latter had supposed some blood to pass from the heart by the arteries and to return to it by the veins; but no one had arrived at an idea of a complete circulation of all the blood through the system, and no one had grasped the consequences involved in such a conception. Harvey's idea of the movement of the heart (De Motu Cordis) was new; his notion of the circulation (et Sanguinis) was new; and his method of demonstrating these was new.
Harvey's Argument.—The gist of Harvey's arguments is indicated in the following propositions quoted with slight modifications from Hall'sPhysiology: (I) The heart passively dilates and actively contracts; (II) the auricles contract before the ventricles do; (III) the contraction of the auricles forces the blood into the ventricles; (IV) the arteries have no "pulsific power,"i.e., they dilate passively, since the pulsation of the arteries is nothing else than the impulse of the blood within them; (V) the heart is the organ of propulsion of the blood; (VI) in passing from the right ventricle to the left auricle the blood transudes through the parenchyma of the lungs; (VII) the quantity and rate of passage of the blood peripherally from the heart makes it a physical necessity thatmost of the blood return to the heart; (VIII) the blood does return to the heart by way of the veins. It will be noticed that the proposition VII is the important one; in it is involved the idea of applying measurement to a physiological process.
Harvey's Influence.—Harvey was a versatile student. He was a comparative anatomist as well as a physiologist and embryologist; he had investigated the anatomy of about sixty animals and the embryology of insects as well as of vertebrates, and his general influence in promoting biological work was extensive.
His work on the movement of the blood was more than a record of a series of careful investigations; it was a landmark in progress. When we reflect on the part played in the body by the blood, we readily see that a correct idea of how it carries nourishment to the tissues, and how it brings away from them the products of disintegrated protoplasm is of prime importance in physiology. It is the point from which spring all other ideas of the action of tissues, and until this was known the fine analysis of vital processes could not be made. The true idea of respiration, of the secretion by glands, the chemical changes in the tissues, in fact, of all the general activities of the body, hinge upon this conception. It was these consequences of his demonstration, rather than the fact that the blood moves in a circuit, which made it so important. This discovery created modern physiology, and as that branch of inquiry is one of the parts of general biology, the bearing of Harvey's discovery upon biological thought can be readily surmised.
Those who wish to examine Harvey's views at first hand, without the burden of translating them from the Latin, will find an edition of his complete works translated into English by Willis, and published by the Ray Society, of London.
As is always the case with new truths, there was hostilityto accepting his views. In England this hostility was slight on account of his great personal influence, but on the Continent there was many a sharp criticism passed upon his work. His views were so illuminating that they were certain of triumph, and even in his lifetime were generally accepted. Thus the new conception of vital activities, together with his method of inquiry, became permanent parts of biological science.
CHAPTER IV
THE INTRODUCTION OF THE MICROSCOPE AND THE PROGRESS OF INDEPENDENT OBSERVATION
Theintroduction of the microscope greatly increased the ocular powers of observers, and, in the seventeenth century, led to many new departures. By its use the observations were carried from the plane of gross anatomy to that of minute structure; the anatomy of small forms of life, like insects, began to be studied, and also the smaller microscopic animalcula were for the first time made known.
Putting aside the disputed questions as to the time of the invention and the identity of the inventor of the microscope—whether to Fontana, Galileo, or the Jenssens belongs the credit—we know that it was improved by the Hollander Drebbel in the early years of the seventeenth century, but was not seriously applied to anatomical studies till after the middle of that century.
The Pioneer Microscopists
The names especially associated with early microscopic observations are those of Hooke and Grew in England, Malpighi in Italy, and Swammerdam and Leeuwenhoek, both in Holland. Their microscopes were imperfect, and were of two kinds: simple lenses, and lenses in combination, forming what we now know as the compound microscope. Some forms of these early microscopes will be described and illustrated later. Although thus early introduced, microscopic observation did not produce its great results until the nineteenth century, just after magnifying-lenses had been greatly improved.
Fig. 12.—Hooke's Microscope, 1665.From Carpenter'sThe Microscope and Its Revelations. Permission of P. Blakiston's Sons & Co.
Robert Hooke (1635-1703), of London, published in 1665 a book of observations with the microscope entitledMicrographia, which was embellished with eighty-three plates of figures. Hooke was a man of fine mental endowment, who had received a good scientific training at the University of Cambridge, but who lacked fixedness of purpose in the employment of his talents. He did good work in mathematics, made many models for experimenting with flying machines, and claimed to have discovered gravitation beforeNewton, and also the use of a spring for regulating watches before Huygens, etc. He gave his attention to microscopic study for a time and then dropped it; yet, although we can not accord to him a prominent place in the history of biology, he must receive mention as a pioneer worker with the microscope. His book gave a powerful stimulus to microscopy in England, and, partly through its influence, labor in this field was carried on more systematically by his fellow-countryman Nehemiah Grew.
The form of the microscope used by Hooke is known through a picture and a description which he gives of it in hisMicrographia. Fig. 12 is a copy of the illustration. His was a compound microscope consisting of a combination of lenses attached to a tube, one set near the eye of the observer and the other near the object to be examined. When we come to describe the microscopes of Leeuwenhoek, with which so much good work was accomplished, we shall see that they stand in marked contrast, on account of their simplicity, to the somewhat elaborate instrument of Hooke.
Grew (1628-1711) devoted long and continuous labor to microscopic observation, and, although he was less versatile and brilliant than Hooke, his patient investigations give him just claim to a higher place in the history of natural science. Grew applied the microscope especially to the structure of plants, and his books entitledIdea of a Philosophical History of Plants(1673) andAnatomy of Vegetables(1682) helped to lay the foundations of vegetable histology. When we come to consider the work of Malpighi, we shall see that he also produced a work upon the microscopic structure of plants which, although not more exact and painstaking than Grew's, showed deeper comprehension. He is the co-founder with Grew of the science of the microscopic anatomy of plants.
It is not necessary to dwell long upon the work of eitherHooke or Grew, since that of Malpighi, Swammerdam, and Leeuwenhoek was more far-reaching in its influence. The publications of these three men were so important, both in reference to microscopic study and to the progress of independent investigation, that it will be necessary to deal with them in more detail. In the work of these men we come upon the first fruits of the application of the methods introduced by Vesalius and Harvey. Of this triumvirate, one—Malpighi—was an Italian, and the other two were Hollanders. Their great service to intellectual progress consisted chiefly in this—that, following upon the foundations of Vesalius and Harvey, "they broke away from the thraldom of mere book-learning, and relying alone upon their own eyes and their own judgment, won for man that which had been quite lost—the blessings of independent and unbiased observation."
It is natural that, working when they did, and independently as they did, their work overlapped in many ways. Malpighi is noteworthy for many discoveries in anatomical science, for his monograph on the anatomy of the silkworm, for observations of the minute structure of plants, and of the development of the chick in the hen's egg. Swammerdam did excellent and accurate work upon the anatomy and metamorphosis of insects, and the internal structure of mollusks, frogs, and other animals. Leeuwenhoek is distinguished for much general microscopic work; he discovered various microscopic animalcula; he established, by direct observation, the fact of a connection between arteries and veins, and examined microscopically minerals, plants, and animals. To him, more than to the others, the general title of "microscopist" might be applied.
Since these men are so important in the growth of biology, let us, by taking them individually, look a little more closely into their lives and labors.
Marcello Malpighi, 1628-1694
Personal Qualities.—There are several portraits of Malpighi extant. These, together with the account of his personal appearance given by Atti, one of his biographers, enable us to tell what manner of man he was. The portrait shown in Fig. 13 is a copy of the one painted by Tabor and presented by Malpighi to the Royal Society of London, in whose rooms it may still be seen. This shows him in the full attractiveness of his early manhood, with the earnest, intellectual look of a man of high ideals and scholarly tastes, sweet-tempered, and endowed with the insight that belongs to a sympathetic nature. Some of his portraits taken later are less attractive, and the lines and wrinkles that show in his face give evidence of imperfect health. According to Atti, he was of medium stature, with a brown skin, a delicate complexion, a serious countenance, and a melancholy look.
Accounts of his life show that he was modest, quiet, and of a pacific disposition, notwithstanding the fact that he lived in an atmosphere of acrimonious criticism, of jealousy and controversy. A family dispute in reference to the boundary-lines between his father's property and the adjoining land of the Sbaraglia family gave rise to a feud, in which representatives of the latter family followed him all his life with efforts to injure both his scientific reputation and his good name. Under all this he suffered acutely, and his removal from Bologna to Messina was partly to escape the harshness of his critics. Some of his best qualities showed under these persecutions; he was dignified under abuse and considerate in his reply. In reference to the attacks upon his scientific standing, there were published after his death replies to his critics that were written while he was smarting under their injustice and severity, but these replies are free from bitterness and are written in a spirit of great moderation. The following picture, taken from Ray's correspondence, shows the fine control of his spirit. Under the date of April, 1684, Dr. Tancred Robinson writes: "Just as I left Bononia I had a lamentable spectacle of Malpighi's house all in flames, occasioned by the negligence of his old wife. All his pictures, furniture, books, and manuscripts were burnt. I saw him in the very heat of the calamity, and methought I never beheld so much Christian patience and philosophy in any man before; for he comforted his wife and condoled nothing but the loss of his papers."
Fig. 13.—Malpighi, 1628-1694.
Education.—Malpighi was born at Crevalcuore, near Bologna, in 1628. His parents were landed peasants, or farmers, enjoying an independence in financial matters. As their resources permitted it, they designed to give Marcellus, their eldest child, the advantage of masters and schools. He began a life of study; and, before long, he showed a taste for belles-lettres and for philosophy, which he studied under Natali.
Through the death of both parents, in 1649, Malpighi found himself orphaned at the age of twenty-one, and as he was the eldest of eight children, the management of domestic affairs devolved upon him. He had as yet made no choice of a profession; but, through the advice of Natali, he resolved, in 1651, to study medicine. This advice followed, in 1653, at the age of twenty-five, he received from the University of Bologna the degree of Doctor of Medicine.
University Positions.—In the course of a few years he married the sister of Massari, one of his teachers in anatomy, and became a candidate for a chair in the University of Bologna. This he did not immediately receive, but, about 1656, he was appointed to a post in the university, and began his career as a teacher and investigator. He must have shown aptitude for this work, for he was soon called to the University of Pisa, where, fortunately for his development,he became associated with Borelli, who, as an older man, assisted him in many ways. They united in some work, and together they discovered the spiral character of the heart muscles. But the climate of Pisa did not agree with him, and after three years he returned, in 1659, to teach in the University of Bologna, and applied himself assiduously to anatomy.
Here his fame was in the ascendant, notwithstanding the machinations of his enemies and detractors, led by Sbaraglia. He was soon (1662) called to Messina to follow the famous Castelli. After a residence there of four years he again returned to Bologna, and as he was now thirty-eight years of age, he thought it time to retire to his villa near the city in order to devote himself more fully to anatomical studies, but he continued his lectures in the university, and also his practice of medicine.
Honors at Home and Abroad.—Malpighi's talents were appreciated even at home. The University of Bologna honored him in 1686 with a Latineulogium; the city erected a monument to his memory; and after his death, in the city of Rome, his body was brought to Bologna and interred with great pomp and ceremony. At the three hundredth anniversary of his death, in 1894, a festival was held in Bologna, his monument was unveiled, and a book of addresses by eminent anatomists was published in his honor.
During his lifetime he received recognition also from abroad, but that is less remarkable. In 1668 he was elected an honorary member of the Royal Society of London. He was very sensible of this honor; he kept in communication with the society; he presented them with his portrait, and deposited in their archives the original drawings illustrating the anatomy of the silkworm and the development of the chick.
In 1691 he was taken to Rome by the newly elected pope, Innocent XII, as his personal physician, but under these newconditions he was not destined to live many years. He died there, in 1694, of apoplexy. His wife, of whom it appears that he was very fond, had died a short time previously. Among his posthumous works is a sort of personal psychology written down to the year 1691, in which he shows the growth of his mind, and the way in which he came to take up the different subjects of investigation.
In reference to his discoveries and the position he occupies in the history of natural science, it should be observed that he was an "original as well as a very profound observer." While the ideas of anatomy were still vague, "he applied himself with ardor and sagacity to the study of the fine structure of the different parts of the body," and he extended his investigations to the structure of plants and of different animals, and also to their development. Entering, as he did, a new and unexplored territory, naturally he made many discoveries, but no man of mean talents could have done his work.
Activity in Research.—During forty years of his life he was always busy with research. Many of his discoveries had practical bearing on the advance of anatomy and physiology as related to medicine. In 1661 he demonstrated the structure of the lungs. Previously these organs had been regarded as a sort of homogeneous parenchyma. He showed the presence of air-cells, and had a tolerably correct idea of how the air and the blood are brought together in the lungs, the two never actually in contact, but always separated by a membrane. These discoveries were first made on the frog, and applied by analogy to the interpretation of the lungs of the human body. He was a comparative anatomist, and the first to insist on analogies of structure between organs throughout the animal kingdom, and to make extensive practical use of the idea that discoveries on simpler animals can be utilized in interpreting the similar structures in the higher ones.
It is very interesting to note that in connection with this work he actually observed the passage of blood through the capillaries of the transparent lungs of the frog, and also in the mesentery. Although this antedates the similar observations of Leeuwenhoek (1669), nevertheless the work of Leeuwenhoek was much more complete, and he is usually recognized in physiology as the discoverer of the capillary connection between arteries and veins. At this same period Malpighi also observed the blood corpuscles.
Soon after he demonstrated the mucous layer, or pigmentary layer of the skin, intermediate between the true and the scarf skin. He had separated this layer by boiling and maceration, and described it as a reticulated membrane. Even its existence was for a long time controverted, but it remains in modern anatomy under the title of the Malpighian layer.
His observation of glands was extensive, and while it must be confessed that many of his conclusions in reference to glandular structure were erroneous, he left his name connected with the Malpighian corpuscles of the kidney and of the spleen. He was also the first to indicate the nature of the papillæ on the tongue. The foregoing is a respectable list of discoveries, but much more stands to his credit. Those which follow have a bearing on comparative anatomy, zoölogy, and botany.
Monograph on the Structure and Metamorphosis of the Silkworm.—Malpighi's work on the structure of the silkworm takes rank among the most famous monographs on the anatomy of a single animal. Much skill was required to give to the world this picture of minute structure. The marvels of organic architecture were being made known in the human body and the higher animals, but "no insect—hardly, indeed, any animal—had then been carefully described, and all the methods of the work had to be discovered." Helabored with such enthusiasm in this new territory as to throw himself into a fever and to set up an inflammation in the eyes. "Nevertheless," says Malpighi, "in performing these researches so many marvels of nature were spread before my eyes that I experienced an internal pleasure that my pen could not describe."
He showed that the method of breathing was neither by lungs nor by gills, but through a system of air-tubes, communicating with the exterior through buttonhole shaped openings, and, internally, by an infinitude of branches reaching to the minutest parts of the body. Malpighi showed an instinct for comparison; instead of confining his researches to the species in hand, he extended his observations to other insects, and has given sketches of the breathing-tubes, held open by their spiral thread, taken from several species.
The nervous system he found to be a central white cord with swellings in each ring of the body, from which nerves are given off to all organs and tissues. The cord, which is, of course, the central nervous system, he found located mainly on the ventral surface of the body, but extending by a sort of collar of nervous matter around the œsophagus, and on the dorsal surface appearing as a more complex mass, or brain, from which nerves are given off to the eyes and other sense organs of the head. As illustrations from this monograph we have, in Fig. 14, reduced sketches of the drawings of the nervous system and the food canal in the adult silkworm. The sketch at the right hand illustrates the central nerve cord with its ganglionic enlargement in each segment, the segments being indicated by the rows of spiracles at the sides. The original drawing is on a much larger scale, and reducing it takes away some of its coarseness. All of his drawings lack the finish and detail of Swammerdam's work.
He showed also the food canal and the tubules connectedwith the intestine, which retain his name in the insect anatomy of to-day, under the designation of Malpighian tubes. The silk-forming apparatus was also figured and described. These structures are represented, as Malpighi drew them, on the left of Fig. 14.
Fig. 14.—From Malpighi'sAnatomy of the Silkworm, 1669.
This monograph, which was originally published in 1669 by the Royal Society of London, bears the Latin title,Dissertatio Epistolica de Bombyce. It has been several times republished, the best edition being that in French, which datesfrom Montpellier, in 1878, and which is prefaced by an account of the life and labors of Malpighi.
Anatomy of Plants.—Malpighi's anatomy of plants constitutes one of his best, as well as one of his most extensive works. In the folio edition of his works, 1675-79, theAnatome Plantarumoccupies not less than 152 pages and is illustrated by ninety-three plates of figures. It comprises an exposition of the structure of bark, stem, roots, seeds, the process of germination, and includes a treatise on galls, etc., etc.
In this work the microscopic structure of plants is amply illustrated, and he anticipated to a certain degree the ideas on the cellular structure of plants. Burnett says: "His observations appear to have been very accurate, and not only did he maintain the cellular structure of plants, but also declared that it was composed of separate cells, which he designated 'utricles.'" Thus did he foreshadow the cell theory of plants as developed by Schleiden in the nineteenth century. When it came to interpretations, he made several errors. Applying his often-asserted principle of analogies, he concluded that the vessels of plants are organs of respiration and of circulation, from a certain resemblance that they bear to the breathing-tubes of insects. But his observations on structure are good, and if he had accomplished nothing more than this work on plants he would have a place in the history of botany.
Work in Embryology.—Difficult as was his task in insect anatomy and plant histology, a more difficult one remains to be mentioned,viz., his observations of the development of animals. He had pushed his researches into the finer structure of organisms, and now he attempted to answer this question: How does one of these organisms begin its life, and by what series of steps is its body built up? He turned to the chick, as the most available form in which to get an insight into this process, but he could not extend his observations successfully into periods earlier than about the twenty-four-hour stage of development. Two memoirs were written on this subject, both in 1672, which were published by the Royal Society of England under the titlesDe Formatione Pulli in OvoandDe Ovo Incubato. Of all Malpighi's work, this has received the least attention from reviewers, but it is, for his time, a very remarkable achievement. No one can look over the ten folio plates without being impressed with the extent and accuracy of his observations. His sketches are of interest, not only to students of embryology, but also to educated people, to see how far observations regarding the development of animals had progressed in 1672. Further consideration of his position in embryology will be found in the chapter on the rise of that subject.
Little is known regarding the form of microscope employed by Malpighi. Doubtless, much of his work was done with a simple lens, since he speaks of examining the dried lungs with a microscope of a single lens against the horizontal sun; but he is also known to have observed with an instrument consisting of two lenses.
Malpighi was a naturalist, but of a new type; he began to look below the surface, and essayed a deeper level of analysis in observing and describing the internal and minute structure of animals and plants, and when he took the further step of investigating their development he was anticipating the work of the nineteenth century.
Jan Swammerdam(1637-1680)
Swammerdam was a different type of man—nervous, incisive, very intense, stubborn, and self-willed. Much of his character shows in the portrait by Rembrandt represented in Fig. 15. Although its authenticity has been questioned, it is the only known portrait of Swammerdam.
Early Interest in Natural History.—He was born in 1637, nine years after Malpighi. His father, an apothecary of Amsterdam, had a taste for collecting, which was shared by many of his fellow-townsmen. The Dutch people of this time sent their ships into all parts of the world, and this vast commerce, together with their extensive colonial possessions, fostered the formation of private museums. The elder Swammerdam had the finest and most celebrated collection in all Amsterdam. This was stored, not only with treasures, showing the civilization of remote countries, but also with specimens of natural history, for which he had a decided liking. Thus "from the earliest dawn of his understanding the young Swammerdam was surrounded by zoölogical specimens, and from the joint influence, doubtless, of hereditary taste and early association, he became passionately devoted to the study of natural history."
Studies Medicine.—His father intended him for the church, but he had no taste for theology, though he became a fanatic in religious matters toward the close of his life; at this period, however, he could brook no restraint in word or action. He consented to study medicine, but for some reason he was twenty-six years old before entering the University of Leyden. This delay was very likely owing to his precarious health, but, in the mean time, he had not been idle; he had devoted himself to observation and study with great ardor, and had already become an expert in minute dissection. When he went to the University of Leyden, therefore, he at once took high rank in anatomy. Anything demanding fine manipulation and dexterity was directly in his line. He continued his studies in Paris, and about 1667 took his degree of Doctor of Medicine.
Fig. 15.—Swammerdam, 1637-1680.
During this period of medical study he made some rather important observations in human anatomy, and introduced the method of injection that was afterward claimed byRuysch. In 1664 he discovered the valves of lymphatic vessels by the use of slender glass tubes, and, three years later, first used a waxy material for injecting blood-vessels.
It should be noted, in passing, that Swammerdam was the first to observe and describe the blood corpuscles. As early as 1658 he described them in the blood of the frog, but not till fifty-seven years after his death were his observations published by Boerhaave, and, therefore, he does not get the credit of this discovery. Publication alone, not first observation, establishes priority, but there is conclusive evidence that he observed the blood corpuscles before either Malpighi or Leeuwenhoek had published his findings.
Love of Minute Anatomy.—After graduating in medicine he did not practice, but followed his strong inclination to devote himself to minute anatomy. This led to differences with his father, who insisted on his going into practice, but the self-willed stubbornness and firmness of the son now showed themselves. It was to gratify no love of ease that Swammerdam thus held out against his father, but to be able to follow an irresistible leading toward minute anatomy. At last his father planned to stop supplies, in order to force him into the desired channel, but Swammerdam made efforts, without success, to sell his own personal collection and preserve his independence. His father died, leaving him sufficient property to live on, and brought the controversy to a close soon after the son had consented to yield to his wishes.
Boerhaave, his fellow-countryman, gathered Swammerdam's complete writings after his death and published them in 1737 under the titleBiblia Naturæ. With them is included a life of Swammerdam, in which a graphic account is given of his phenomenal industry, his intense application, his methods and instruments. Most of the following passages are selected from that work.
Intensity as a Worker.—He was a very intemperateworker, and in finishing his treatise on bees (1673) he broke himself down.
"It was an undertaking too great for the strongest constitution to be continually employed by day in making observations and almost as constantly engaged by night in recording them by drawings and suitable explanations. This being summer work, his daily labors began at six in the morning, when the sun afforded him light enough to enable him to survey such minute objects; and from that time till twelve he continued without interruption, all the while exposed in the open air to the scorching heat of the sun, bareheaded, for fear of interrupting the light, and his head in a manner dissolving into sweat under the irresistible ardors of that powerful luminary. And if he desisted at noon, it was only because the strength of his eyes was too much weakened by the extraordinary efflux of light and the use of microscopes to continue any longer upon such small objects.
"This fatigue our author submitted to for a whole month together, without any interruption, merely to examine, describe, and represent the intestines of bees, besides many months more bestowed upon the other parts; during which time he spent whole days in making observations, as long as there was sufficient light to make any, and whole nights in registering his observations, till at last he brought his treatise on bees to the wished-for perfection."
Method of Work.—"For dissecting very minute objects, he had a brass table made on purpose by that ingenious artist, Samuel Musschenbroek. To this table were fastened two brass arms, movable at pleasure to any part of it, and the upper portion of these arms was likewise so contrived as to be susceptible of a very slow vertical motion, by which means the operator could readily alter their height as he saw most convenient to his purpose. The office of one of these arms was to hold the little corpuscles, and that of the other to applythe microscope. His microscopes were of various sizes and curvatures, his microscopical glasses being of various diameters and focuses, and, from the least to the greatest, the best that could be procured, in regard to the exactness of the workmanship and the transparency of the substance.
"But the constructing of very fine scissors, and giving them an extreme sharpness, seems to have been his chief secret. These he made use of to cut very minute objects, because they dissected them equably, whereas knives and lancets, let them be ever so fine and sharp, are apt to disorder delicate substances. His knives, lancets, and styles were so fine that he could not see to sharpen them without the assistance of the microscope; but with them he could dissect the intestines of bees with the same accuracy and distinctness that others do those of large animals.
"He was particularly dexterous in the management of small tubes of glass no thicker than a bristle, drawn to a very fine point at one end, but thicker at the other."
These were used for inflating hollow structures, and also for making fine injections. He dissolved the fat of insects in turpentine and carried on dissections under water.
An unbiased examination of his work will show that it is of a higher quality than Malpighi's in regard to critical observation and richness of detail. He also worked with minuter objects and displayed a greater skill.
The Religious Devotee.—The last part of his life was dimmed by fanaticism. He read the works of Antoinette Bourignon and fell under her influence; he began to subdue his warm and stubborn temper, and to give himself up to religious contemplation. She taught him to regard scientific research as worldly, and, following her advice, he gave up his passionate fondness for studying the works of the Creator, to devote himself to the love and adoration of that same Being. Always extreme and intense in everything he undertook, he likewise overdid this, and yielded himself to a sort of fanatical worship until the end of his life, in 1680. Had he possessed a more vigorous constitution he would have been greater as a man. He lived, in all, but forty-three years; the last six or seven years were unproductive because of his mental distractions, and before that, much of his time had been lost through sickness.
The Biblia Naturæ.—It is time to ask, What, with all his talents and prodigious application, did he leave to science? This is best answered by an examination of theBiblia Naturæ, under which title all his work was collected. His treatise on Bees and Mayflies and a few other articles were published during his lifetime, but a large part of his observations remained entirely unknown until they were published in this book fifty-seven years after his death. In the folio edition it embraces 410 pages of text and fifty-three plates, replete with figures of original observations. It "contains about a dozen life-histories of insects worked out in more or less detail. Of these, the mayfly is the most famous; that on the honey-bee the most elaborate." The greater amount of his work was in structural entomology. It is known that he had a collection of about three thousand different species of insects, which for that period was a very large one. There is, however, a considerable amount of work on other animals; the fine anatomy of the snail, the structure of the clam, the squid; observations on the structure and development of the frog; observations on the contraction of the muscles, etc., etc.
It is to be remembered that Swammerdam was extremely exact in all that he did. His descriptions are models of accuracy and completeness.
Fig. 16 shows reduced sketches of his illustrations of the structure of the snail. The upper sketch shows the central nervous system and the nerve trunks connected therewith, and the lower figure shows the shell and the principal muscles.This is an exceptionally good piece of anatomization for that time, and is a fair sample of the fidelity with which he worked out details in the structure of small animals. Besides showing this, these figures also serve the purpose of pointing out that Swammerdam's fine anatomical work was by no means confined to insects. His determinations on the structure of the young frog were equally noteworthy.
Fig. 16.—From Swammerdam'sBiblia Naturæ.
But we should have at least one illustration of his handling of insect anatomy to compare more directly with that of Malpighi, already given. Fig. 17 is a reduced sketch of the anatomy of the larva of an ephemerus, showing, besides other structures, the central nervous system in its natural position. When compared with the drawings of Malpighi, we see there is a more masterly hand at the task, and a more critical spirit back of the hand. The nervous system is very well done, and the greater detail in other features shows a disposition to go into the subject more deeply than Malpighi.
Besides working on the structure and life-histories of animals, Swammerdam showed, experimentally, the irritability of nerves and the response of muscles after their removal from the body. He not only illustrates this quite fully, but seems to have had a pretty good appreciation of the nature of the problem of the physiologist. He says:
"It is evident from the foregoing observations that a great number of things concur in the contraction of the muscles, and that one should be thoroughly acquainted with that wonderful machine, our body, and the elements with which we are surrounded, to describe exactly one single muscle and explain its action. On this occasion it would be necessary for us to consider the atmosphere, the nature of our food, the blood, the brain, marrow, and nerves, that most subtle matter which instantaneously flows to the fibers, and many other things, before we could expect to attain a sight of the perfect and certain truth."
In reference to the formation of animals within the egg, Swammerdam was, as Malpighi, a believer in the pre-formation theory. The basis for his position on this question will be set forth in the chapter on the Rise of Embryology.
Fig. 17.—Anatomy of an Insect: Dissected and Drawn by Swammerdam.
There was another question in his time upon which philosophers and scientific men were divided, which was in reference to the origin of living organisms: Does lifeless matter, sometimes, when submitted to heat and moisture, spring into life? Did the rats of Egypt come, as the ancients believed, from the mud of the Nile, and do frogs and toads have a similar origin? Do insects spring from the dew on plants? etc., etc. The famous Redi performed his noteworthy experiments when Swammerdam was twenty-eight years old, but opinion was divided upon the question as to the possible spontaneous origin of life, especially among the smaller animals. Upon this question Swammerdam took a positive stand; he ranged himself on the side of the more scientific naturalists against the spontaneous formation of life.
Antony van Leeuwenhoek(1632-1723)
In Leeuwenhoek we find a composed and better-balanced man. Blessed with a vigorous constitution, he lived ninety-one years, and worked to the end of his life. He was born in 1632, four years after Malpighi, and five before Swammerdam; they were, then, strictly speaking, contemporaries. He stands in contrast with the other men in being self-taught; he did not have the advantage of a university training, and apparently never had a master in scientific study. This lack of systematic training shows in the desultory character of his extensive observations. Impelled by the same gift of genius that drove his confrères to study nature with such unexampled activity, he too followed the path of an independent and enthusiastic investigator.
The portrait (Fig. 18) which forms a frontispiece to hisArcana Naturærepresents him at the age of sixty-three, and shows the pleasing countenance of a firm man in vigorous health. Richardson says: "In the face peering through the big wig there is the quiet force of Cromwell and the delicate disdain of Spinoza." "It is a mixed racial type, Semitic and Teutonic, a Jewish-Saxon; obstinate and yet imaginative; its very obstinacy a virtue, saving it from flying too far wild by its imagination."
Recent Additions to His Biography.—There was a singular scarcity of facts in reference to Leeuwenhoek's life until 1885, when Dr. Richardson published inThe Asclepiad[1]the results of researches made by Mr. A. Wynter Blyth in Leeuwenhoek's native town of Delft. I am indebted to that article for much that follows.