Popular Science Monthly/Volume 58/April 1901/Malpighi, Swammerdam and Leeuwenhoek

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THE

POPULAR SCIENCE

MONTHLY

 

APRIL, 1901.




MALPIGHI, SWAMMERDAM AND LEEUWENHOEK.
By Professor WILLIAM A. LOCY,

NORTH WESTERN UNIVERSITY.

AS Cuvier justly remarks, the seventeenth century was a fruitful one for science. It was then that the method of investigating nature by direct observation and experiment was reestablished. After the long period of intellectual decline, the mental life of mankind was to be lifted again to the level it had attained in the age of the highest development of Greek philosophy. The complete arrest of inquiry into the domain of nature and the adherence to tradition had lasted so long that the faculty of testing and experimeting seemed to be almost extinct. The unfriendliness of the ecclesiastics and other intellectual authorities to investigation, and the dire consequences to the individual of a movement towards intellectual freedom, served to repress the natural desire of the human intellect for a knowledge of itself and the universe. Any one who broke over the restraints went against every appeal to self-interest, and deserved much credit for independence and courage.

Nevertheless, in this untoward atmosphere the spirit of unbiased inquiry was awakened through the efforts of a few independent minds; among these select few, who, as pioneers in the revival of exact science, have an enduring interest for all educated people, we must remember Malpighi, Swammerdam and Leeuwenhoek. Although their work marks an epoch, they were not the only pioneers, nor the first ones; Vesalius, Galileo, Harvey and Descartes had started the reform movement in which our triumvirate so worthily labored.

One of these men—Malpighi—was an Italian, and the other two were Netherlands Dutchmen. Their great service "consisted chiefly in this, that they broke away from the thraldom of book-learning, and, relying alone upon their own eyes and their own judgment, won for man that which had been quite lost, the blessing of independent and unbiased observation." The importance of this step for its broad-reaching effects even upon the intellectual life of our own time is not easily overestimated. Much of the work of the present is built upon the foundations they laid.

There is a singularly unappreciative attitude towards scientific work, of the biological kind, done before 1850, and a widespread disposition to look upon the advances of the present time as peculiarly our own, based wholly upon 'modern' work and 'modern' methods. This sometimes takes the extreme form, in the rising generation of practical workers, of looking upon the scientific investigations of the past ten years as of necessarily better quality than those of any preceding period, because they are the most recent. But this is to do injustice to our predecessors, and it is wholesome to take a look into the past, to see some of the fine observational work done long ago, and to be compelled to recognize the continuity of biological development, both as regards work and ideas.

If it were Johannes Müller with whom we were to deal, a marvel could be shown, but the work of Malpighi. Swammerdam and Leeuwenhoek belongs to a period a century and a half before his time. For these men it is just to claim, in addition to the service indicated above, the possession of the true scientific spirit, the introduction of the microscope and of more exact methods into scientific investigation, and, through their work, the beginning of that better comprehension of the natural universe that we call modern science.

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 on the minute structure of plants and on the development of the chick in the hen's egg. Together with Grew, he is regarded as the founder of plant histology. Swammerdam did excellent and accurate work on 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 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.

Let us, by taking them individually, look a little more closely at the lives and labors of these men.

 
MARCELLUS MALPIGHI. 1628-1694.

There are several portraits of Malpighi extant. These, together with the account of his personal appearance given by Atti,[1] enable us to tell what manner of man he was. The portrait given here is the

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Fig. 1. Marcellus Malpighi.

one painted by Tabor, and presented by Malpighi to the Royal Society of London. As Pettigrew says, 'it shows a countenance highly intellectual, and as a work of art is of no mean importance.' Some of the other portraits are less attractive, and give evidence of imperfect health in the lines and wrinkles of his face. According to Atti, he was of medium stature, with a brown skin, delicate complexion, a serious countenance and 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. 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 attack and moderate in reply. In.his posthumous works his replies to his critics are free from bitterness and written in a spirit of great moderation. This picture from Kay's correspondence shows the same 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."

Malpighi was born at Crevalcuore, near Bologna, in 1694. His parents were farmers, or landed peasants; enjoying a certain independence in financial matters, they designed to give Marcellus, their eldest child, the advantages of masters and the schools. He began a life of study, and 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, at the age of twenty-one, an orphan, and, as the eldest of eight children, domestic affairs devolved upon him. He had as yet made no choice of profession, but, through the advice of Natali, he resolved, in 1651, to study medicine, and, in 1653, at the age of twenty-five, he received from the University of Bologna the degree of M. D.

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 position 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 teacher and investigator. He must have shown aptitude for this work, for soon he was called to the University of Pisa, where, fortunately for his development, he became associated with Borelli, who was older and 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. He retired to a villa near the city, and devoted himself to anatomical studies.

Malpighi's talents were appreciated even at home. The University of Bologna honored him Id 1686 with a Latin eulogium, the city erected a monument to his memory, and after his death, in the city of Eome, his body was brought to Bologna and interred with great pomp and ceremony. He also received recognition 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 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 new conditions 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 deserves the title of 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'; he extended his studies to the structure of plants and different animals, and a]so to development. Entering as he did, a new and unexplored territory, he, of course, made many discoveries, but no man of mean talents could have done his work. He used every method at his command for investigating the structure of tissues and animal forms—macerating, boiling, injections of ink and colored fluids, and also applied the microscope to the discovery of tissues.

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 aircells, and had a tolerably correct idea of how the air and 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 bcdy. He was 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, 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 observations on glands were 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 the spleen. He was also the first to indicate the presence of papillæ on the tongue. This is a respectable list of discoveries, but much more stands to his credit. Those which follow have a bearing on comparative anatomy, zoology 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 mo insect—hardly, indeed, any animal—had then been carefully described, and all the methods of work had to be discovered.' The delicacy, beauty and intricacy of the organic systems in this group of animals were well calculated to arouse wonder and admiration. He worked 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." In the words of Miall:

"We must recall the complete ignorance of insect-anatomy which then prevailed, and remember that now for the first time the dorsal vessel, the tracheal system, the tubular appendages of the stomach, the reproductive organs, and the structural changes which
accompany transformation were observed, to give any adequate credit to the writer of this masterly study. Treading A new path, he walks steadily forward, trusting to his own sure eves and cautious judgment. The descriptions are brief and simple, the figures clear, inn not rich in detail. There would now be much to add to Malpighi's account, but hardly anything to correct. The only positive mistakes which meet the eye relate to the number of spiracles and nervous ganglia—mistakes promptly corrected by Swammerdam."

He showed that the method of breathing was neither by lungs nor gills, but through a system of air-tubes, communicating with the exterior through button-hole shaped openings, and. internally, by an infinitude

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Fig. 2. From Malpighi's Anatomy of the Silkworm.

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 he gives 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 tissue. 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 the monograph we have, in Fig. 2, reduced sketches of the drawings of the nervous system and the food canal in the adult silkworm. The sketch at the left hand illustrates the central nerve cord, and the small one near the center shows one ganglion enlarged, and part of the breathing tubes connected with it. 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 connected with the intestine, which retain his name in the insect anatomy of to-day, under the designation of malpighian tubules. The silk-forming apparatus was also figured and described. These structures are represented, as Malpighi drew them, on the right of Fig. 2.

This monograph, which was originally published in Latin in 1669, has been several times republished. The best edition is that in French, dating from Montpellier, in 1878, and which is preceded 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, the 'Anatome Plantarum' occupies not less than 152 pages and is illustrated by ninety-three plates of figures. It comprises the structure of bark, stem, roots, seeds, process of germination, treatise on galls, etc., etc.

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 of this work: "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 of his observations, 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 observational work on structure is 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 work in insect anatomy and plant histology, a more difficult one remains to be mentioned, viz., his observations on 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 stops is its body built up? He turned to the chick, as the most available form in which to gel 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. Of all Malpighi's work, this has received the least attention from reviewers, but it is, for the time, a very remarkable piece of work. No one can

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Fig. 3. Malpighi's Sketches showing the Embryological Development of the Chick.

took over the ten folio plates without being impressed with the extent and accuracy of his observations. His earliest sketches show an open neural groove with an enlargement for the head end, and from this stage onward he carries the development of the chick by sketches to the period of hatching. These sketches are of interest not only to students of embryology, but also to educated people, to see how far observations upon the development of animals had progressed in 1672. His are, doubtless, the earliest figures ever made showing the comparatively early stages of development. Harvey's observations on development, published in 1631, were not accompanied by illustrations, and the sketches of Fabricius, ab aqua pendente, published in 1604, werefar surpassed* by Malpighi's, the youngest stages represented being much older than his.

Fig. 3 shows a group of selected sketches from different plates, but they fail to give an adequate idea of the extent of the work, taken as a whole. It is very interesting to note the figures showing the formation of the heart and aortic arches. The execution of the figures in this work is less coarse than those on the silkworm.

The embryological thought of his time was dominated by the theory of preformation or predelineation. Just as when we examine a seed, we find within an embryo plantlet, so it was supposed that the minute embryos of all animal life existed in miniature within the egg. Harvey had expressed himself against it, and the doctrine was overthrown by Wolff in the following century. Malpighi's position, however, was based on actual observation; he was not able to find by examination any stage in which there was no evidence of organization. Dareste says that he examined eggs in a very hot August, in which there is reason to believe that developmental changes had gone forward to a considerable degree. Be this as it may, the imperfection of his instruments and methods would have made it very difficult to have seen anything definitely in stages below twenty-four hours. As a result of his experience, he says:

"When we undertake to discover the principle of life of animals in the egg we are astonished to find the animal already formed there; thus our labor is vain, for as soon as we encounter the first movement of life we are obliged to recognize parts that are visible to our eyes. * * *

On this account, it may be necessary to declare that the first beginnings preexist in the egg," etc. In his posthumous works he "is less circumspect, and goes even to the point of describing the mechanism of evolution of these primitive elements."

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.

 
JOHN 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. Although its authenticity has been questioned, it is the only portrait[2] known of Swammerdam.

He was born in 1637, nine years after Malpighi. His father, an apothecary of Amsterdam, had a taste for collecting, which was shared

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Fig. 4. Jan Swammerdam.

by many of his fellow-townsmen. "The vast commerce and extended colonial empire of the Holland of that day 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 zoological specimens, and from the joint influence, doubtless, of hereditary taste and early association, he became passionately devoted to the study of natural history."

His father intended him for the church, but he had no taste for divinity, though he became a fanatic in religious matters towards the close of his life; at this period 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 due to his precarious health, but. in the meantime, 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, therefore, he at once took high rank in anatomy. Anything demanding fine manipulation and skill was directly in his line.

At Leyden he studied anatomy under the renowned Sylvius and surgery under Van Horne. He also continued his studies in Paris, and about 1667 took his M. D. degree.

During this period of medical study he made some rather important observations in human anatomy, and introduced the method of injection that was afterwards claimed by Ruysch. In 1664 he discovered the values 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 his observations were not published till fifty-seven years after his death by Boerhaave, and, therefore, he does not get the credit of this discovery. Publication alone establishes priority, not first observation, but there is conclusive evidence that he observed the blood corpuscles before either Malpighi or Leeuwenhoek had published their observations.

After graduating in medicine he did not practise, but followed his st long inclination to devote himself to minute anatomy. This led to differences with his father, who insisted on his going into practise, but the self-willed stubbornness and firmness of his nature showed themselves. It was from no love of ease that Swammerdam thus held out against his father, but to be able to follow ah irresistible leading towards minute anatomy. At last his father was planning 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 his complete writings after his death and published them in 1737 under the title 'Biblia Naturæ.' This is preceded by 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.

He was a very intemperate worker, 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 6 in the morning, when the sun afforded him light enough to enable him to survey such minute objects; and from that time till 12 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.

"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 apply the 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 in detail. He also worked with minuter objects and displayed a greater skill. As one writer says:

"He had in the highest degree all the attributes which mark the eminent observer. In delicate and subtle manipulation, in contriving new methods to meet every case, in acute and accurate perception, he has never been surpassed and rarely equaled."

United with these exceptional talents as an observer was a mystical quality of mind that made his interpretations less happy, and often led him to strange ideas. It is an interesting psychological combination. His observations are accurate, but his interpretations fanciful. For instance, in observing the transformations of insects, he came to a stage in which he could see the parts of the adult insect encased, as it were, in the pupa. This led him to see, in fancy, an evidence of encasement of one generation within another in all animals and to adhere to that curious idea of emboitement, which had so many believers in his time. He even saw in this the proof, to his mind, that the germs of all forthcoming generations of mankind were originally located in the common mother Eve, all closely encased one within the other, like the boxes of a Japanese juggler. The end of the world was by him conceived of as a necessity when the last germ of this wonderful series had become unfolded.

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 loving and adoring that same Being. Always extreme and intense in everything lie 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 from his mental distractions, and before that much of his time had been lost by sickness.

It is time to ask, with all his talents and prodigious application, what did he leave to science? This is best answered by an examination of the 'Biblia Naturaæ’ into which alt his work was collected. His treatise on 'Bees and Mayflies' and a few other articles were published during his lifetime, hut 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 honeybee the most

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Fig. 5. From Swammerdam's 'Biblia Naturæ.'

elaborate." The greater amount of his work was in structural entomology. It is known that he had a collection of about 3,000 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, structure of the clam, the squid; observations on the structure and development of the frog: observations on the contraction of 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. 5 shows reduced sketches of his illustrations of the structure of the snail, and also of the larva of an insect. The upper sketch on the left-hand side shows the central nervous system and the nerve trunks connected therewith, and the lower figure on the same side shows the shell and the principal muscles. This is an exceptionally good piece of anatomical work for the 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 work on the structure of the young frog was equally noteworthy.

But we should have at least one illustration of his handling of insect anatomy to com j are more directly with that of Malpighi, already given (p. 567)-The right-hand side of Fig. 5 is a reduced sketch of the anatomy of the larva of an ephemeras, compared with the work of Malpighi; we see there a more masterly hand at the work, 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 work deeper than Malpighi.

Besides work on structure and life histories, 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 preformation theory. The basis for his position on this question has already been stated.

There was another question in his time upon which philosophers and scientific men were divided, that w T as 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 had performed his noteworthy experiments the year after Swammerdam's birth, 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 origin of life. In reference to this matter he says:

"In attentively examining the development of insects, of animals with blood, and vegetables, one recognizes that all these beings grow and develop according to one law, and one feels how false is the opinion that attributes to fortuitous causes such regular and constant effects."
 

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Fig. 6. Antonius A. Leeuwenhoek.

 
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, lie was born in 1632, four years after Malpighi and five before Swammerdam; they were, therefore, strictly speaking, contemporaries, lie 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 studies. 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 which forms a frontispiece to his 'Arcana Naturæ' represents 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."

There was a singular scarcity of facts in reference to Leeuwenhoek's life until 1885, when Dr. Richardson published in 'The Asclepiad'[3] 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.

His 'Arcana Naturæ' and other scientific letters contained a complete record of his scientific activity, but 'about his parentage, his education and his manner of making a living there was nothing but conjecture to go upon.' The few scraps of personal history were contained in the 'Encyclopædia' articles by Carpenter and others, and these were wrong in sustaining the hypothesis that Leeuwenhoek was an optician or manufacturer of lenses for the market. Although he ground lenses for his own use, there was no need on his part of increasing his financial resources by their sale. He held under the court a minor office designated 'Chamberlain of the Sheriff.' The duties of the office were those of a beadle, and were set forth in his commission, a document still extant. The requirements were light, as was also the salary, amounting to about £26 a year. He held this post for thirty-nine years, and the stipend was thereafter continued to him to the end of his life.

Van Leeuwenhoek was derived from a good Delft family. His grandfather and great-grandfather were Delft brewers, and his grandmother a brewer's daughter. The family doubtless were wealthy. His schooling seems to have been brought to a close at the age of sixteen, when he was 'removed to a clothing business in Amsterdam, where he filled the office of bookkeeper and cashier.' After a few years he returned to Delft, and at the age of twenty-two he married and gave himself up largely to studies in natural history. Six years after his marriage he obtained the appointment designated above. He was twice married, but left only one child, a daughter by his first wife.

He led an easy, prosperous, but withal a busy life. The microscope had recently been invented, and for observation with that new instrument Leeuwenhoek showed an avidity amounting to a passion.

"That he was in comfortable if not affluent circumstances is clear from the character of his writings; that he was not troubled by any very anxious and responsible duties is certain from the continuity of his scientific work; that he could secure the services of persons of influence is discernible from the circumstances that, in 1673, De Graaf sent his first paper to the Royal Society of London; that in 1680 the same society admitted him as fellow; that the directors of the East India Company sent him specimens of natural history, and that, in 1698, Peter the Great paid him a call to inspect his microscopes and their revelations."

Leeuwenhoek seems to have been fascinated by the marvels of the microscopic world, but the extent and quality of his work lifted him above the level of the dilettante. He was not, like Malpighi and Swammerdam, a skilled dissector, but turned his microscope in all directions; in the mineral, as well as the vegetable and animal kingdoms. Just when he began to use the microscope is not known; his first publication in reference to microscopic objects did not appear till 1673, when he was forty-one years old. He gave good descriptions and drawings of his instruments, and those still in existence have been described by Carpenter and others, and, therefore, we have a very good idea of his working equipment. During his lifetime he sent as a present to the Royal Society of London twenty-six microscopes, each provided with an object to examine. Unfortunately, these were removed from the rooms of the society and lost during the eighteenth century. His lenses were of fine quality and were ground by himself. 'They were nearly all simple lenses of small size, but considerable curvature, and needed to be brought close to the object examined. He had different microscopes for different purposes, giving a range of magnifying powers from 40 to 270 diameters and possibly higher. The number of his lenses is surprising; he possessed not less than 2-47 complete microscopes, two of which were provided with double lenses and one with a triplet. In addition to the above he had 172 lenses set between plates of metal, which gives a total of 419 lenses used by him in his observations. Three were of quartz, or rock crystal, the rest were of glass. More than one-half the lenses were mounted in silver, three were in gold.

It is to be understood that all his microscopes were of simple construction; no tubes, no mirror; simply pieces of metal to hold the magnifying-glass and the objects to be examined, with screws to adjust the position and the focus. We shall perhaps get the best idea of how they were used and brought into focus by reference to Fig. 7, which is copied from Richardson's article in 'The Asclepiad." This shows the way the instrument was arranged to examine the circulation of blood in the transparent tail of a small fish. The fish was placed in water in a slender glass tube, and the latter was held in a metallic frame, to which a plate (marked D) was joined, carrying the magnifying glass. The latter is indicated in the circle above the letter D, near the tail fin of the fish. The eye was applied close to this circular magnifying glass, which was brought into position and adjusted by means of screws. The two small sketches show a front and a back view of another one of his microscopes. The small circle shows the position of the lens inserted in a metallic plate. On the opposite side was a sort of object holder, whose position was controlled by screws. In some instances, he had a concave reflector with a hole in the center, in which his magnifying-glass

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Fig. 7. Leeuwenhoek's Microscope. Fig. 8. Capillary Circulation, after Leeuwenhoek.

was inserted, and, in this form of the instrument, the objects were illuminated by reflected and not by transmitted light.

His microscopic observations were described and sent to learned societies in the form of letters. "All or nearly all that he did in a literary way was after the manner of an epistle," and these were so numerous as to justify the cognomen, 'The man of many letters.' "The French Academy of Sciences, of which he was elected a corresponding member in 169?', got twenty-seven; hut the lion's share fell to the young Royal Society of London, which in fifty years—1673-1723— ceived 375 letters and papers." "The works themselves, except that they lie in the domain jf natural history, are disconnected and appear in no order of systematized study. The philosopher was led by what transpired at any moment to lead him."

In 1686 he observed the minute circulation and demonstrated the capillary connection between arteries and veins. This was perhaps his most important observation for its bearing on physiology. It must be remembered that Harvey had not actually seen the circulation of the blood, which he announced in 1628. He assumed on entirely sufficient grounds the existence of a complete circulation, but there was wanting in his scheme the direct ocular proof of the passage of blood from arteries to veins. This was supplied by Leeuwenhoek. Fig. 8 shows one of his sketches of the capillary circulation. In his efforts to see the circulation he tried various animals; the comb of the young cock, the ears of white rabbits, the membraneous wing of the hat were progressively examined. The next advance came when he directed his microscope to the tail of the tadpole. Upon examining this he exclaims:

"A sight presented itself more delightful than any mine eyes had ever beheld; for here I discovered more than fifty circulations of the blood, in different places, while the animal lav quiet in the water, and I could bring it before my microscope to my wish. For I saw not only that in many places the blood was conveyed through exceedingly minute vessels, from the middle of the tail towards the edges, but that each of the vessels had a curve or turning, and carried the blood back towards the middle of the tail, in order to be again conveyed to the heart. Hereby it plainly appeared to me that the blood-vessels which I now saw in the animal, and which bear the names of arteries and veins, are, in fact, one and the same; that is to say, that they are properly termed arteries so long as they convey the blood to the furtherest extremities of its vessels, and veins when they bring it back to the heart. And thus it appears that an artery and a vein are one and the same vessel prolonged or extended."

This description shows that he fully appreciated the course of the minute vascular circulation and the nature of the communication between arteries and veins. He afterwards extended his observations to the web of the frog's foot, the tail of young fishes and eels.

In this connection it should be remembered that Malpighi, in 1661, observed the flow of blood in the lungs and mesentery of the frog, but he made little of it. Leeuwenhoek did much more with his discovery, and gave the first clear idea of the capillary circulation. Leeuwenhoek was also anticipated by Malpighi in reference to the microscopic structure of the blood. (See also under Swammerdam.) To Malpighi the corpuscles appeared to be globules of fat, while Leeuwenhoek noted that the blood discs of birds, frogs and fishes were oval in outline and those of mammals circular. He reserved the name of 'globule' for those of the human body, erroneously believing them to be spheroidal.

Among his other discoveries bearing on physiology and medicine may be mentioned: The branched character of heart muscles, the stripe in voluntary muscles, the structure of the crystalline lens, the description of spermatozoa after they had been pointed out to him in 1674 by Hamen, a medical student in Leyden, etc. Richardson dignifies him with the title, 'The Founder of Histology,' but this, in view of the work of his great contemporary, Malpighi, seems to me an overestimate.

Turning his microscope in all directions, he examined water and found it peopled with minute animalcules, those simple forms of animal life, propelled through the water by innumerable hair-like cilia, extending from the body like banks of oars from a galley, except that in many cases they extend from all surfaces. He saw not only the animalcules, but also the cilia that move their bodies.

His descriptions of the various forms of these animalcules are interesting, and m strangely archaic language. Here is one of them, changed from Dutch into English:

"In the year 1675 I discovered living creatures in rain-water which had stood but four days in a new earthern pot, glazed blew within. This invited me to view this water with great attention, especially those little animals appearing to me ten thousand times less than those represented by Mons. Swammerdam, and by him called waterflies or waterlice, which, may be perceived in the water with the naked eye. The first sort by me discovered in the said water, I divers times observed to consist of five, six, seven or eight clear globules, without being able to discover any film that held them together or contained them. When these animalcula, or living atoms, did move they put forth two little horns, continually moving themselves; the place between these two horns was flat, though the rest of the body was roundish, sharpening a little towards the end, where they had a tayle, near four times the length of the whole body, of the thickness (by my microscope) of a spider's web; at the end of which appeared a globule, of the bigness of one of those which made up the body; which tayle I could not perceive even in very clear water to be mov'd by them. These little creatures, if they chanced to light upon the least filament or string, or other such particle, of which there are many in the water, especially after it has stood some days, they stook entangled therein, extending their body in a long round, and striving to dis-entangle their tayle; whereby it came to pass, that their whole body lept back towards the globule of the tayle, which then rolled together serpent-like, and after the manner of copper or iron wire, that having been wound around a stick, and unwound again, retains those windings and turnings," [4] etc.

"Any one who has examined under the microscope the well-known bull animalcule will recognize in this first description of it the stalk and its form after contraction in the 'tayle which retains those windings and turnings.'

He discovered also the Rotifers, those favorites of the amateur microscopists, made so familiar to the general public in works like Gross's 'Evenings at the Microscope.' He showed their remarkable powers of resuscitation after complete drying. He observed that when water containing these animalcules evaporated they were reduced to fine dust, but became alive again after great lapses of time by the introduction of water.

He made many observations on the microscopic structure of plants. Fig. 9 gives a fair sample of the extent to which he observed the cellular construction of vegetables and anticipated the cell-theory.

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Fig. 9. From Leeuwenhoek's 'Arcana Nature.'

While Malpighi's work in that field was more extensive, these sketches from Leeuwenhoek represent very well the character of the work of the period on minute structure of plants.

It remains to say that on the two biological questions of the day he took a decided stand. He was a believer in preformation or predelineation of the embryo in an extreme degree, seeing in fancy the complete outline of both maternal and paternal individuals in the spermatozoa, and going so far as to make sketches of the same. But upon the question of the spontaneous origin of life he took the side that has been so triumphantly demonstrated in this century against the occurrence of spontaneous generation.

 

We see in these three gifted contemporaries different personal characteristics. Leeuwenhoek, the composed and strong, attaining an age of ninety-one; Malpighi, always in feeble health, but directing his efforts with rare capacity, reaching the age of sixty-seven; while the great intensity of Swammerdam stopped his scientific career at thirty-six and burned out his life at the age of forty-three.

They were all original and accurate observers, but there is variation in the kind and quality of their intellectual product. The two university-trained men showed capacity for coherent observations; they were both better able to direct their efforts towards some definite end; Leeuwenhoek, with the advantages of vigorous health and long working period, lacked the systematic training of the schools, and all his life worked in discursive fashion; he left no coherent piece of work of any extent like Malpighi's 'Anatome Plantarum' or Swammerdam's 'Anatomy and Metamorphosis of Insects.'

Swammerdam was the most critical observer of the three, if we may judge by his work in the same field as Malpighi's on the silkworm. His descriptions are models of accuracy and completeness, and his anatomical work shows a higher grade of finish and completeness than Malpighi's. Malpighi, it seems to me, did more in the sum total than either of the others to advance the sciences of anatomy and physiology and through them the interests of mankind. Leeuwenhoek had larger opportunity; he devoted himself to microscopic observation's, but he wandered over the whole field. While his observations lose all monographic character, nevertheless they were important in opening new fields and advancing the sciences of anatomy, physiology, botany and zoology.

The combined force of their labors marks an epoch in the establishment of the scientific method and in the ushering in of a new grade of intellectual life.

  1. Atti. 'Notizie Edite ed Inedite Delia Vita e Delle Opére Di Marcelli Malpighi De Lorenzo Bellini. Bologna, 1847; 4°: 52.5 pp.
  2. I am indebted to Professor Dr. Hoffman, of Leyden, for this copy.
  3. 'Leeuwenhoek and the Rise of Histology.' Asclepiad, Vol. II.; 1885.
  4. 'Kent's Manual of the Infusoria.' Vol. 1, p. 3. Taken from the 'Philosophical Transactions' for the rear 1677.