Popular Science Monthly/Volume 37/June 1890/Sketch of Theodor Schwann
|SKETCH OF THEODOR SCHWANN.|
By M. LÉON FRÉDÉRICQ.
ON the 23d of January, 1878, was celebrated at the University of Liége, by the scientific men of Belgium and others representing neighboring European states and more distant countries, the fortieth anniversary of the professorship of Theodor Schwann. Men of all nations joined, by their presence or by letter, in honoring the man who, as the founder of the cell theory, had showed that all the varied and complex manifestations of Nature are one in kind, and had given a new direction to physiological research.
The object of this demonstration, Theodor Schwann, was born on the 7th of December, 1810, at Neuss, near Düsseldorff, in Rhenish Prussia, and died in Liége, in January, 1882. His father and grandfather were goldsmiths; but the father, after Theodor was born, established a printing-office—himself, with the aid of an artisan, constructing the first press—which has become one of the most prosperous concerns of the kind in the Rhenish country. From it was issued the memorial volume published in 1879 in honor of Theodor Schwann.
The youth inherited from his father a decided taste for manual occupations, which afterward proved of great assistance to him in his laboratory work. While still a child he used to spend his play-hours in making miniature instruments of physics with the most primitive materials. From the primary school he went into the humanitarian courses in the pro-gymnasium of his native village, and thence, for the completion of his studies, to the Jesuit College at Cologne. His lively intelligence and assiduity attracted the attention of all his teachers. He exhibited a marked predilection for mathematical and scientific studies, especially in physics.
He was still undecided as to the career he should choose, when he enrolled himself, in October, 1829, in the class in philosophy at Bonn. His family were deeply religious, and would have been glad to see him become a clergyman like his elder brother Peter, who died in 1881, Professor of Theology and honorary canon at Frauenburg. Therefore he began with a mixed course, including metaphysical and logical studies, along with those in mathematics and science. The latter branches in the end absorbed all his attention, and he decided to study medicine.
He became the pupil of the anatomist and physiologist Johann Müller, and that fixed his destiny. Müller, with a full appreciation of Schwann's abilities, made him an associate in his labors, and they experimented together on the motor and sensitive roots of the spinal nerves, and on the coagulation of the blood. Having passed the philosophical and scientific examinations at Bonn, Schwann went to Würzburg, where he passed three semesters, and then removed to Berlin to complete his studies and go through his final examinations. He found Müller here again, as Professor of Anatomy and Physiology, and under his direction performed the investigation on the necessity of oxygen to the development of the embryo in the hen's egg, on which was based his inaugural dissertation on receiving the degree of doctor of medicine.
Müller, insisting upon Schwann's following a scientific career, had him appointed in 1834 aid at the Anatomical Museum, of which he was director. The position was an extremely modest one, and not at all pleasant. The late Director of the Berlin Museum, Peters, speaks of having seen Schwann at work for whole days scraping the fins of a giant ray while preparing its skeleton; and many of the specimens in the zoölogical collections bear witness to the conscientious care with which he performed this monotonous work. The five years which Schwann spent here with Müller were a period of intense application, marked by a succession of discoveries. All the great works which illustrate his name date from this epoch.
A characteristic portrait of Schwann as he appeared at this time has been drawn by Henle, who passed several years under the same roof with him. He says: "He was a man of stature below the medium, with a beardless face, an almost infantine and always smiling expression, smooth, dark-brown hair, wearing a fur-trimmed dressing-gown, living in a poorly lighted room on the second floor of a restaurant which was not even of the second class. He would pass whole days there without going out, with a few rare books around him and numerous glass vessels, retorts, vials, and tubes, simple apparatus which he made himself. Or I go in thought to the dark and fusty halls of the Anatomical Institute, where we used to work till nightfall by the side of our excellent chief, Johann Müller. We took our dinner in the evening, after the English fashion, so that we might enjoy more of the advantage of daylight. Our porter's wife furnished the meat, we the wine and wit. Those were happy days which the present generation might envy us; happy days when the first good microscopes had been sent out from the shops of Plössi at Vienna, or of Pistor and Schick at Berlin, which we paid for by exercising a student's economies; happy days, when it was still possible to make a first-class discovery by scraping an animal' membrane with the nail or cutting it with the scalpel." Müller had at that time begun the publication of his great treatise on physiology, a work of scientific criticism into which he admitted nothing as true that had not been verified by himself or by his assistants under his eyes. Schwann, at his instigation, undertook a number of physiological and microscopical researches for this work. He examined the texture of the voluntary muscles; pointed out a method of isolating the primary fibers, and demonstrated the origin of the transverse striæ of their primitive bundles. He sought for the terminations of the nerves in the muscles, without being able to discover them. He did not accept the ansated termination, which was generally believed in then, but has now been disproved. He first determined the existence of the proper walls of the capillary vessels, and came very near discovering their endothelium. He demonstrated, by physiological experiments with cold water, the muscular contractibility of the arteries. He discovered in the mesentery of the frog and the tail of the tadpole the division of the primitive fiber of the nerves, an observation then without precedent. He first proved, by microscopical examination and by the re-establishment of the function, the restorableness of cut nerves; and he first made use of that faculty in approaching the question of learning whether the sensitive or motor fibers, when stimulated in their middle parts, propagate the irritation toward both the center and periphery at once, or only in one direction. He invented the muscular balance, for measuring the force of the muscle in different states of contraction. He demonstrated that muscular contractility follows the same law as the elasticity of a body which, having the same length as the muscle at its maximum contraction, is stretched out to the length of the muscle at rest. This work on muscular force was the beginning of the series of researches by the aid of which Du Bois-Reymond, Helmholtz, and others have built up the general physiology of the nerves and muscles. It was the first instance, says Du Bois-Reymond, of the examination of an eminently vital force as if it were a physical one, and of the mathematical expression in figures of the laws of its action.
Schwann assisted, with the professors at Berlin, in the preparation of the Encyclopedic Dictionary of the Medical Sciences, to which he contributed the articles on vessels, hematose, urinary secretion, and cutaneous secretion. At this period, also, he began the experiments which led up to the discovery of the digestive ferment, pepsin; and the principles which he set forth on the subject are essentially the same as are still taught, the elucidation of a few details being all that has been added.
In one of the theses attached to his inaugural dissertation, Schwann had opposed the theory of spontaneous generation, which had begun to prevail again, after a general abandonment of Spallanzani's germ theory. The absence of microbes from preparations which had been hermetically sealed was attributed to the deprivation of oxygen. Schwann and Franz Schulze labored independently to disprove this view. Schulze showed that vegetable and animal infusions could be preserved for months in the presence of air and after renewing supplies of air, if the air was first passed over sulphuric acid to kill the germs in it. Schwann communicated to the Society of German Naturalists and Physicians the results of similar experiments, and of others in which he destroyed the germs by calcination. He explained putrefaction as a work of decomposition by the germs developing themselves at the expense of the organic substance, in proof of which he showed that arsenic and corrosive sublimate, which were poisonous to infusoria, were also the best preservatives against putrefaction. It remained to be shown that the calcination of the air did not deprive it of its essential properties of sustaining respiration and promoting alcoholic fermentation—for the advocates of spontaneous generation might say that the development of life was prevented by asphyxiation. Schwann's view was sustained when he found that frogs suffered no inconvenience in calcined air; but, when it came to apply the test to the fermentation of alcohol, no fermentation took place. Schwann was not discouraged by this, but proclaiming a new discovery, that yeast was an organic growth, and working out experiments to prove it, converted the apparently hostile result into an additional support to his theory. These ideas did not receive at once the support they deserved. They had a formidable adversary in Liebig, who set forth another theory of fermentation, and ridiculed them with a parody. Schwann, averse to controversy, made no answer to Liebig's contradictions or to his joke. He bided his time. It came in a quarter of a century, when Schwann saw his theoryextended to cover a great variety of chemical and pathological actions, and almost universally accepted; and received in 1878, from Pasteur, who had carried it to its highest triumph, a letter recognizing him as the one who had opened the road by following which his own wonderful discoveries were made.
These researches might of themselves have sufficed to make the name of Schwann illustrious. But they are relatively but little known because their fame has been dimmed in the face of the incomparable luster of his great discovery of the cell theory. The publication of the book in which the basis of this theory was laid down opened a new era in biological study. We might search in vain, says Simon, in his History of the Natural Sciences, for an example of a more radical revolution in the direction and character of scientific labors than that which was effected in 1838 and 1839 by the publication of Schwann's histogenetic theory. The revolution was sudden, and triumphed, we might say, without resistance. As Henle has remarked, the scientific soil in which this theory took root and grew had been prepared from two different points of view: one, philosophical or ideal; the other, positive or histological. The philosophical preparation dated from the beginning of the study of Nature, and was illustrated in the propensity of the human mind to look for some simple cause for the diversity of phenomena. To this we owe the monads of Epicurus and Leibnitz, Oken's philosophy of Nature, and many other efforts ancient and modern. On the other side, certain histological researches, often very modest, but coming close to the facts, had prepared a way for the cell theory. Robert Brown had discovered the cellular nucleus in 1831; Mirbel, Von Mohl, and Unger had demonstrated that the organs and tissues of plants were at bottom aggregations of cells in different degrees of transformation. Schleiden had been studying the important part played by the nucleus in the formation of vegetable cells, and had given it the name of cytoblast; and other authors had found in animals organs formed of cells. But these were as yet only isolated facts.
Schwann has himself told the story of the way the idea of his discovery first occurred to him. "One day," he says, "when I was dining with M. Schleiden, that illustrious botanist spoke of the important part which the nucleus plays in the development of plant-cells. I at once recollected that I had seen a similar organ in the cells of the dorsal cord, and instantly appreciated the extreme importance the discovery would have if I could show that it plays the same part there as the nucleus of plants in the development of vegetable cells. It must follow, in fact, in consequence of the identity of so characteristic phenomena, that the cause which produces the cells of the dorsal cord could not be different from the one that gives origin to the vegetable cells." The two men went together to the amphitheatre of anatomy to examine the nucleuses in question, and Schleiden recognized a complete resemblance between them and the nucleuses of the cells of plants. "From that time," Schwann continues, "all my efforts were directed to finding proof of the pre-existence of the nucleus in the cell." And he goes on to tell how his views were confirmed as his researches advanced. At the time Schwann thus undertook to show that all the organs are of cellular origin, the structure of most of them was very imperfectly known. The application of the microscope to researches in animal histology was of recent introduction, and everything was to create. Schwann did not shrink from the tremendous task which opened up before him; and what he had done first for the cartilages and the dorsal cord, he tried in succession for all the other bodily tissues; and in all he had the joy of seeing his idea confirmed.
Schwann came upon many new discoveries in the course of these investigations. He first compared the egg to a cell, and recognized cells in the globules of the blastoderm; described the stellar pigmentary cells, the layers of the nail, the development of feathers, the nucleuses of the prisms of the enamel, those of the smooth and striated muscles, the fibers of the dental pulp, the cells destined to be transformed into fibers of the crystalline, etc. He called attention to the envelope of the nervous fibers which bears his name as the sheath of Schwann—all of which discoveries have been confirmed by modern research armed with its more perfect technic and superior instruments. The theory of the cell as the primordial element of all the tissues was hereafter to serve as the Ariadne's thread to the numerous investigators who devoted themselves to the study of morphology, ' and was to help them explain the infinite variety of organic forms. It gave a definite purpose to the application of the microscope to investigations in anatomy and physiology. It was the foundation of modern physiology? and all the morphological progress accomplished during nearly the past half-century has grown out from it. Except for its having familiarized the conception of the constitutional unity of living matter, and having declared the principle that every cell is the product of another cell, the doctrine of selection and descent could not, in the opinion of Edward Van Beneden, have gained ground. Its salutary influence in pathological anatomy and the advance of physiology was immediate and great. Acting in another direction, it put an end to the theory of a special vital force, which was in full sway when it was first promulgated, and raised up that of physico-chemical action, which has taken its place. How was it possible to reconcile the notion of cellular individuality with the existence of a single vital force, presiding over the working of all the functions? It would be necessary to reject such a hypothesis and seek the reason of vital phenomena in the properties of molecules and atoms, or else to assign a vital force in miniature to each cell. Schwann insisted that the hypothesis was both superfluous and insufficient. He could not conceive its existence unless it possessed the attributes of intelligent beings; and preferred to seek the cause of the final purpose in nature in the Creator rather than in the creature.
Schwann was just putting in press the book containing his microscopical researches and his later results, when he was invited, in his twenty-ninth year, to take the place of Windischman as Professor of Anatomy at Louvain. His position at Berlin was pleasant, but overmodest, and offered no near prospects for promotion. So he accepted the proffer, and prepared at the end of 1838 to remove. He had to meet a considerable difficulty, in the beginning of his career at Louvain, from the necessity of speaking in French; but his lectures were successful, and still form the basis of instruction in microscopic anatomy at the university. During his term here he published a memoir on the uses of the bile, the results of which, while it gave a new operation in physiological technics, have not been fully confirmed; applied Quetelet's method of statistics to physiological phenomena; and attempted the artificial production of organic elements.
In 1848, Spring, of the University of Liége, finding the combined labors of the chairs of Physiology, General Anatomy, and Comparative Anatomy too much for a single professor to perform, asked to be relieved of a part of his burden. Schwann was selected to fill the place, and was installed in November of the same year Professor of Anatomy, Spring reserving to himself the branches of osteology and myology till 1853, when the whole course came under Schwann's charge. Some opposition was expressed at first to the coming of a stranger to the university; but this soon passed away, for the brilliant reputation of the new professor, the excellence of his teaching, and the loyalty and amenity of his disposition silenced hostile comment, and won hearts to him. In later years he refused several offers of brilliant scientific positions in Germany—from Breslau in 1852, Würzburg and Munich in 1854, and Giessen in 1855. In 1858 he exchanged the chair of Descriptive Anatomy for that of Human Physiology, and in 1870 became an emeritus professor.
Clearness, order, and method are described by those who attended his lectures as the characteristic qualities of Schwann's teaching. His courses in physiology were eminently demonstrative and experimental. Laboratory work always presented a great attraction to him. He was interested in the development of scientific technics, and regularly made himself acquainted with new instruments and methods. He had qualities of heart corresponding with the superiority of his mind. His pupils recollect the quiet good-will and fatherly kindness which he showed toward them, and returned them with grateful demonstrations.
Although he was actively engaged in scientific pursuits during the whole of his long career, he never mingled in the discussions of the learned world after he went to Belgium. During the five years of his residence in Berlin, his discoveries followed upon one another like the explosions of a piece of fire-works; and all the great discoveries that made his name illustrious and opened new horizons to scientific thought date from that time. After removing to Belgium, he published only one work, his researches on the uses of the bile. He became almost forgotten outside of Belgium, and many, not hearing his name mentioned any more, thought he was dead. This may be charged to his aversion to personal controversy. While the cell theory, as a whole, was established, some of the details gave rise to disputes in which he did not care to engage. Believing that he had reached an ultimate principle which time would only establish more strongly, he was willing to let details take care of themselves. But he never lost his interest in the scientific movement; and, at the time of his death, he was engaged in studying the influence of electrical discharges on the development of the lower beings in organic infusions.
In Schwann's theory all the phenomena of life were explained by the properties of atoms. The cell was an aggregation of atoms obeying the laws of nature as if it were a crystal. Plants and animals were aggregations of cells, likewise machines destitute of spontaneity. But man differed from animals by possessing an immaterial element that lifted him above them and gave him freedom. It was in this way that he escaped materialism, and kept himself in line with the Church, to which he submitted his studies, having even sought and obtained ecclesiastical approval for the cell theory before he would publish it. For many years he was collecting materials for a great philosophical work in which the cell theory should take the proportions of a general theory of organisms. Beginning with the definition of the atom, his Theoria, as he called it, was to include all the manifestations of life. Psychological phenomena and the dogmas of the Catholic religion were to have definite places in it. Death prevented his beginning the final preparation of it; and his heirs could only find in his desk a manuscript of seventy-two sheets entitled Man considered from the Physiological Point of View, as he is, and as he is to he.—Translated for the Popular Science Monthly from the Revue Scientifique.