# Popular Science Monthly/Volume 72/June 1908/Johannes Müller

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* JOHANNES MÜLLER
By Dr. PHILIP B. HADLEY
BROWN UNIVERSITY
IN the present day when the individual laborer in the fields of biology is so often lost in the flood of new facts which is continually being poured into the archives of the science; when a narrow specialization and very definite concentration of activity are the primary condition and means for furthering the highest interests of the science as a whole, and when the difficulty is ever increasing, to hold in the foreground the larger and more general problems of biological significance, it may not be altogether inappropriate to recall—we might almost say revive—at times, some of the monumental figures whom the history of every science, at rare periods, brings forth, and to learn once again our debt to them.
That the times are past when it is permitted a single individual to survey, in full understanding, the broad fields of activity in the realm of general biology must assuredly be considered as a sign of advance. We may even remark that the gradual expansion which physiology alone has undergone during the last half century, in passing beyond the confines of a unitary science and in trespassing—perhaps with right—upon the fields which had at one time belonged to other realms, is a necessary consequent to the death of the last great ruler of the science. For these reasons alone it may be of interest and of profit to recall the single instance of a man who, during his years of activity, so deeply influenced the drift of physiological thought; and after whose death, the overgrown and no longer self-containing science of physiology burst like a great stream at its mouth, by many and devious channels to reach the sea.
Johannes Müller was born in the city of Coblenz on the fourteenth day of July, 1801, the son of Mathias Müller, a shoemaker. Although a man of small means, the father determined not to deny his son the advantages of a fair education, and accordingly the young lad was sent to the Jesuit school in the place of his birth, then under French control. Here he remained for eight years, pursuing a study of the classics and mathematics and gaining the foundation of that knowledge of Greek used so brilliantly in after years in the translation and ​commentation of Aristotle. A few years later we find him at the Gymnasium, where, in spite of the old scholastic system of teaching, he took a deep interest in the study of the animal and plant worlds—an interest which was no doubt stimulated by the reading of Goethe, whose works were a source of great delight to young Müller. During this period there also appears to have developed in him that rich gift of imagination which, as one of his biographers says, is so necessary not only to the poet, but also to the natural investigator. In his later work on the "Phantasmal Phenomena of Vision," Müller tells us how, as a boy, he perceived in the crumbling walls of a neighbor's house all sorts of odd and fantastic figures and faces.
At the age of seventeen, Müller left the Gymnasium and, having served one year in the army—as was customary with the youths of his station—he entered, at the age of eighteen, the University of Bonn, which had just been founded. As has been the case with so many natural scientists, here Müller at first hesitated in making his decision between the church and medicine. Born as he was of Roman Catholic parents and nurtured in the Catholic faith by a strongly believing mother, it is not strange that, even as a child, he manifested a desire to enter the priesthood. But the decision was soon made. For three days, so we are told, young Müller closeted himself in his room in order that he might deliberate. At the expiration of this time he made known his decision to a friend in these words: "I am determined. I shall study medicine; for I know what I have and whom I serve."
While at the University of Bonn, Müller's career was characterized by an intense application to study. He maintained, however, a constant exercise of independent thought, and manifested a keen relish for original investigation. Here he initiated, even in the first year of his studies, a series of experiments upon the "respiration of the fœtus," a subject in which a prize had been offered by the university. This prize Müller secured when at the age of nineteen. In connection with the work, a story which a friend of Müller has made known, is characteristic of the young investigator at this time. He had once started upon a journey on horse to Arrthal and was but a short distance on the way when, by the roadside, he espied a pregnant cat. He immediately gave chase, captured it and, for the time being postponing his journey, carried the animal back to the university, where, by Caesarian section, he deprived it of its young in order that he might consequently solve some point in his first problem of investigation.
During the early part of his period at Bonn, although as a student he was most intent upon his work, he was not wholly indifferent to the general yearning for constitutional freedom which was pervading the thought of the middle and lower classes throughout the German ​states after the expulsion of the French. The movement towards a student alliance was then at its height, and this seized strongly upon Müller, who, as we learn, took a leading part in that rather enthusiastic association in which the academic students still cherished hopes of a German unity.
Even these early investigations of Müller were bringing him to the notice of many of the scientific men of his time. On the occasion of the publication of his work on the "Laws of Animal Motion," Oken, the then famous natural scientist, expressed his high approval together with the wish that Müller might be permitted to devote himself purely to natural science. Of this course of action, however, there seemed at that time little prospect. After the death of Müller's father, the small family inheritance lasted but a short while; and from this time until the dawn of his European fame Müller appears to have been constantly troubled with the distressing problem of obtaining the necessary funds for the continuance of his labors; and often even with the question of obtaining food. But in spite of the difficulties which his financial condition enforced upon him, this was on the whole a gay time. The thoughts of the wide possibilities of his chosen vocation appear to have maintained the spirit of the youth, and the unquenchable thirst for knowledge and recognition was gratified at every spring which philosophy, literature, theoretical natural science and careful observation offered. It was also here and during these early years of his study that Müller contracted the spirit of the Naturphilosophie, from whose grasp he was freed at a later date through his contact with Rudolphi at Berlin.
When we consider the trying conditions which surrounded Müller in this period of his life, it must be considered most fortunate that there stood at the head of the Prussian ministry a man who, more than any other, appears not only to have recognized Müller's genius, but also to have had the ability to loosen the fetters which bound up Müller's great gifts. This man was the Minister von Altenstein; and it was he who, by securing a generous government stipend, made it possible for Müller to spend two years—from the spring of 1823 to the autumn of 1824—in furthering his scientific studies at Berlin, where Müller shortly passed his examination for the license to practise his profession of medicine.
It was here that Müller had the great good fortune to become the favorite pupil of Rudolphi, who at that time was the most formidable enemy to subjective speculation in biological science, and who already had begun to base physiology—rather exclusively, perhaps—on the actual study of animal structure. It was Rudolphi, moreover, who had the liberality to place at Müller's disposal his laboratory, his apparatus, his library, and what was still more advantageous, his constant oversight and advice. Of the encouraging aid which he received ​from that excellent master, Müller afterward spoke in the most grateful terms, and declared that it was through the influence and example of Rudolphi alone that his own scientific pursuits were afterwards turned so fully in the direction of comparative anatomy.
At the expiration of his two years of labor, and immensely enriched in all the fields of natural science, Müller again returned to Bonn, and in 1824 was enrolled as academic lecturer in comparative anatomy and physiology. Two years later, when but twenty-five years old, he was made professor extraordinary in the same branch of science.
The epochs in his activity in investigation which immediately followed upon his return to Bonn have well been called by DuBois Reymond the subjective physiologico-philosophical period. The literary landmarks of this period in Müller's career are two works: First, "On the comparative physiology of the sense of sight in men and animals, with researches on the motions of the eyes and on the sight of man"; second, "Concerning the phantasmal phenomena of vision: a physiological research dealing with the physiological evidence of Aristotle concerning dreams, the philosophies and the arts."
In the former of these two works we find recorded that excellent discovery that the sight of insects (which possess facet-eyes) must be conceived of as a mosaic interpretation of objects; that is, the pictures which the insects themselves see are placed together as in the form of a mosaic. In the second work regarding the "Phantasmal Phenomena of Vision," Müller took up a study, the idea of which reached far back into his earliest youth, when he was accustomed to give free play to his fancy in imagining strange shapes and figures on the plaster-scarred walls of the old buildings. These fanciful appearances, which thus early became so familiar in the imaginings of his boyhood, he submitted in maturer years to searching philosophic scrutiny; and the work in which they are described and discussed is a charming yet masterly application of experiment in anatomy, physiology, physics and psychology. Through the medium of these scientific principles Müller explained the seeing of devils and spirits; the friar, who, after long hours of supplication, sees the desired consecration in the form of a shining cloud; the superstitious, to whom the tempter appears as an evil spirit: these phenomena were for Müller only the results of the passion-aroused conditions in the material substances of their sight.
Of all Müller's labors at this time, greatest importance must be attached to his work in elucidation of the laws of the specific energy of the sense organs. With ingenious experiment he worked out the general law that, in whatever manner a sense organ may be stimulated, it always answers to our consciousness by the method peculiar to it. It was from these and other related investigations that Müller deduced many of his philosophical principles: For instance, that we can not ​understand truly the things of the world outside of ourselves, but are cognizant only of the changes brought about in the sense-substance by the thing itself. From these considerations we can readily understand how Müller was led to adopt the view of subjective idealism.
During this period at Bonn, however, the duties which, as a teacher, Müller imposed upon himself, together with the unremitting employment in the lines of his original investigations with all its concomitant labor and thought, had induced, soon after his marriage in 1827, a state of mental and physical exhaustion. Upon the eve of a nervous break-down he secured a leave of absence from the university and with this a recompense of two hundred thalers which made possible for him a journey up the Rhine and through southern Germany. On this trip he was accompanied by his newly married wife. Soon, however, with bettered health he returned to Bonn, where in 1830 he was made professor ordinary.
This event marks the end of what we may term Müller's fiery subjective period, and the beginning of his great objective physiologico-anatomical period, which covered the years of his most brilliant achievement. He was now devoting himself to many branches of scientific work, especially to his morphological studies. Through his anatomical and systematic researches on the scorpion and spiders, he showed himself worthy to be ranked among the first zoologists of his time. In his work, "On the Development of the Reproductive Organs," which appeared a few years later, Müller traced the development of these organs in man and in animals. Coincident with this he was pursuing his researches into the development of other organs, and produced his treatise on the secreting glands. In this excellent work the phylogenetic and ontogenetic development is considered in both man and the lower animals.
In the latter part of Müller's life at Bonn occurred two significant physiological discoveries: First, he definitely proved, through a convincing series of experiments on the frog, the view which had been first announced by the Englishman, Charles Bell, in 1811: that the anterior roots of the spinal cord are motor, and that the posterior roots are sensory in function. In reality this experiment was simple enough. In a frog Müller cut on one side the anterior and on the other the posterior nerve roots of the spinal cord. On the side on which the posterior roots were cut the frog was wholly insensible, while the side on which the anterior roots were cut remained quite paralyzed. This experiment awakened in the scientific world of that time a storm of applause. The fortunate experimenter journeyed to Paris in order to demonstrate the fact before Alexander von Humboldt and Cuvier. Versalius in Stockholm had the experiment performed by Retziüs. Hardly a year later, Müller announced his discovery of ​the lymph hearts in amphibia; and also the results of his investigations on the coagulation of the blood.
Just and prompt recognition did not fail to follow in the train of these excellent results, and the consequent advancement and improvement in his material condition made possible for him other interesting journeys. In 1828 he visited Goethe. The spring of 1831 he spent in the Leiden Museum in Holland. In the autumn of 1831 we find him in Paris in the company of several of the great natural scientists, as Humboldt, Cuvier, Milne Edwards and others who were there at the time. One significant anecdote of this Paris trip should not be omitted. When for the first time Müller went to call upon Dumereil, the latter was very busy, and, since he did not know whom he had to meet, somewhat peevishly directed Müller to the door. Müller, however, as he was almost thrust out, pushed in his head and called out to Dumereil, "Yes, but the Coecilien in the young stages do have gill openings in their necks!" This thrust, it is needless to say, worked as a magic word to gain a long and pleasant interview between these two investigators.
In the year 1832 Rudolphi died at Berlin, thus leaving vacant the foremost position in anatomy and physiology in Germany. Negotiations were already in progress to secure as Rudolphi's successor Dr. Tiedermann from Heidelberg; but at this point in the proceedings Müller determined upon a unique step. He sent to his old friend and former benefactor, the Minister von Altenstein, copies of his works together with a letter in which he ("believing that the importance of the affair would furnish its own excuses") brought himself prominently into the proposition. He said, in part, that it was no more than right that the first and highest position of the kind in Germany should belong to the greatest among scholars; furthermore, that if this man were not Johann Friedrick Meckel, then he believed himself to be the foremost zoologist and physiologist in Germany.
This letter had results: the Minister von Altenstein at once ordered Müller's nomination; and on Easter, 1833, Müller, not yet thirty-three years old, entered upon his duties as "professor ordinary of anatomy, physiology and pathological anatomy, and director of the Anatomical Museums" in the University of Berlin.
The first fruit of Müller's residence in Berlin was the completion of his "Handbook of Physiology," which he had begun long before he left Bonn. Appearing in three parts, it was at last completed in 1840. These volumes represented a piece of work unparalleled in the field of physiological literature. The only work which could be compared with it was Haller's "Elementa." Müller's labors in preparation for this work included an immeasurable number of single observations with reference to the physiology of the voice, of speech, of hearing, of nerve physiology, of teachings on the blood—all of these rest, ​to a very great extent, upon Müller's own discoveries. The "Handbook of Physiology" was accepted with almost universal accord as the most valuable treatise on general physiology that had appeared in the long interval since the time of Haller. It is perhaps of interest to observe that these two writers have much in common, for in both we perceive the fundamental desire of placing the doctrine of physiology upon a basis of fact. Anatomy, human and comparative, experiments on animals, chemistry and physiological science in its various departments, are all called in to bear upon the investigation of the truths of physiology. As one of his commentators has remarked, Müller in this work, as in his others, takes nothing on trust; every statement, whether matter of fact or of doctrine, is thoroughly tested; difficulties, however perplexing, are never evaded or slurred over; defects, however much they may deface the picture to be presented, are never disguised. The result of each quest, whether success or failure, is honestly told and there is no yielding to the temptation, so powerful with writers of systems, "to round off a ragged subject with smooth plausibilities." The influence of the "Handbook" was immense, and the judgment of it appears to have been conditioned not alone by the physiological data it contained, but also by the collected facts of importance to the medical profession.
With the completion of the "Handbook," Müller's activity in this particular line of work seems to have practically ended. From this time on he engaged himself to a greater extent in the fields of comparative anatomy and zoology; and in these subjects, as also in his physiology, Müller excelled both in the abundance of his observations and in the wide range of his discoveries. In his work on the comparative anatomy of the myxinoid fishes, Müller lays down the morphological plan of the vertebrates in their simplest form. The title conveys but a faint notion of the scope of this work. Although it treats chiefly of the anatomy of this particular family of fishes, it is rich in new and original matter in which the structure is compared with that of other families of fishes, and the facts sagaciously applied to the elucidation of greater questions in animal morphology. Regarding Müller's study of the Echinoderms, we may quote from an address by the president of the Royal Society of London:
Professor Müller early applied himself to the study of the structure and economy of the Echinoderms. After describing in a special memoir the anatomy of Pentacrinus, so interesting as a living representative of the extinct Crinoidea, and publishing, in conjunction with M. Troschel, a systematic arrangement and description of the Asteridea, he was at length happily led to investigate the embryo life of this remarkable class of animals. The field of inquiry upon which he entered had scarcely been trenched upon before, and he has since made it almost wholly his own by persevering researches carried on at the proper seasons of the last nine years, on the shores of the North Sea, Mediterranean and Adriatic. In this way he investigated the larval conditions of four out of the five orders of true Echinoderms, and has successfully sought out and determined the commonplace followed in their development, amidst ​remarkable and unlooked-for deviations in the larval organization and habits of genera even of the same order. His inquiries respecting these animals have made us acquainted with the larval forms, with relations between the larva and future being; and with modes of existence, such as nature has not yet been found to present in any other part of the animal kingdom. Finally with the light thus derived from the study of their development, Professor Müller has subjected the organization of the entire class of Echinoderms, both recent and fossil, to a thorough revision, and has added much that was new, as well as cleared up much that was obscure in regard to their economy, structure and homologies. It is to their researches, which occupy seven memoirs of the Royal Academy of Sciences of Berlin, that more special reference is made in the award of the medal.
It was not long after his arrival at Berlin that Müller established the Archiv für Anatomie und Physiologie. Of this he continued the publication until the time of his death. This journal, during the period of its existence, formed a principal medium of publicity for the labors of the leading physiologists of Germany; and the establishment and continued superintendence of it by Müller, in the midst of other laborious employments, must be regarded as an important service rendered to science.
About this time, independent of Müller, his pupil Schwann, following apparently in the footsteps of Schleiden, made the discovery that the animal organism, just as the plant organism, was composed of elementary cells. Müller appears to have been the first to recognize the great significance of this discovery. He immediately employed the new fact for the explanation of certain disease phenomena and clearly pointed out the agreement between tumors and pathological and embryological development. His excellent work on the finer structure of morbid tumors signifies the beginning of all microscopical investigation in pathological anatomy, and here we see the fountain-head of that stimulus which, brought to bear upon the young investigator Virchow, gave rise to that well-known and comprehensive work on "Cellular Pathology."
Concerning the other events of Müller's life, during the Berlin period, it takes little time to relate. The routine work in the Berlin Anatomical Museum was interrupted only by the scientific expeditions which the desired investigation of the sea fauna afforded. The East and North Sea, Sweden, Norway, the coast of the Adriatic and Mediterranean, from Triest to Messina and Marseilles, formed the territory of Müller's scientific explorations. On one of these trips, in 1855, Müller experienced a serious danger. He was returning with two pupils from a journey to the coast of Norway, when at night the steamer Norge on which he sailed was rammed by another and speedily sank. Nearly fifty people lost their lives; and among them one of Müller's young companions. In a letter to a friend in England, in which Müller gives an account of the disaster, he says that upon finding himself in the water at first he kept himself up by swimming. But having his clothes on, he soon became exhausted and would have ​perished had he not caught hold of a ship's ladder which was floating by. For a long time he held on, and had nearly given up all hope of assistance when he was picked up by a boat from the other vessel. His remaining companion, Dr. Schneider, saved himself in a similar way. This event seems to have had a deep effect upon Müller, and although he still resorted to the seaside, ever afterwards he dreaded to trust himself on shipboard.
When, for a second time, Müller was chosen director of the Berlin Museum, it was certainly most unfortunate that his directorship fell in that memorable year of the revolution, 1848. Although Müller felt himself to be truly German, he was apparently no more of a politician than Goethe. He could experience no sympathy for the democratic rashness which on all sides of him was now being manifested. It was a time of civil commotion when political agitation distracted the whole academic being, and both students and professors were deserting the laboratory and lecture room to equip themselves as soldiers of the revolution. Müller, whose quick spirit had led him, in the olden days of the Student Alliance, to take so active a part in the threatened political eruption, had become a sober conservative. His situation was now one of difficulty, and not without peril. He strove manfully to maintain authority, and even those who took a different view of passing events paid willing tribute to his honesty of purpose and to the personal courage he displayed in the most trying circumstances when the university buildings had become the center of the intense revolutionary movement. Müller naturally feared the destruction of the priceless treasures of his collection. Regarding the state of his mind we can obtain some conception from the words of his distinguished scholar, Rudolph Virchow, who upon Müller's own request became his follower as professor of anatomy and physiology at Berlin University. Regarding these days of the revolution, Virchow has written as follows:
He trembled for the safety of the university, for whose treasures he felt himself to be personally responsible. Day and night he remained at the museum, ever on guard. He tore down agitating placards. He ventured with personal danger among the students. On the day of the great citizens' parade, with his own hand he seized away the black banner which was stretched across the balcony of the university building. But the movement more and more escaped the authority of the academic jurisdiction. In the teaching body of the university grew the voicing of disharmony. The professors and the private lecturers made diligent efforts to be heard and some of them (appointed as a committee, to which I also belonged) argued the matter with the director and the senate in a very unpleasant conversation.
Thus it is apparent that Müller was asked in the most kindly spirit to give up, at least temporarily, the position as director; for Virchow continues:
This was, perhaps, the most unfortunate directorship since the ​founding of the university; for the man who possessed the least political inclination was called upon to display, in that time of agitation, the abilities of the politician and statesman.
From this time on Müller worked as hard as ever, but with sadly altered spirits. The nervous strain of overwork was beginning to tell. He suffered much from sleeplessness and this condition he fought with larger doses of opium, which in turn led to a more serious trouble of the heart. In the winter of 1856-7 his health received the first open shock when a gastric fever, the first serious illness since 1827, necessitated the giving up of his lectures. In these days he worried much about himself, feared typhoid fever and wrote to his son, Max Müller, at Cologne. He set in order all his private affairs and engaged, in the case of his death, Dr. Diffenbach to open his body. At this time, however, he developed only a slight trouble in the joint of one foot, and the next summer found him again in fair health. The following winter, however, he again overburdened himself with work, suffered even more than ever from lack of sleep, and again resorted to large doses of alkaloids. For some time he had suffered from moments of dizziness, but had become accustomed to attribute them to the long hours he spent bending over his microscope. These attacks now became so frequent that he dared not venture even on his library ladder. In the evening one would see him sitting listless in his easy chair; or, as if driven by a deep inner anxiety, and gloomy foreboding, pacing restlessly at night through the secluded streets of Berlin.
Easter of the year 1858 did not bring him the accustomed feeling of satisfaction at having completed a period of uninterrupted scientific work. At the end of the summer semester he fully realized, but all too late, the necessity of taking the most energetic measures to bring about an improvement in the condition of his health. He again called his son from Cologne, and, after a consultation, decided to give up all his work and lectures in physiology. He planned an early consultation with his physician in order to decide more definitely regarding his future work; but the end came suddenly. On the morning of the day when this consultation was to have taken place, Müller was found in his bed, lifeless, April 28, 1858. It is needless to say that the tidings of the sudden end of his laborious and valuable life caused profound sorrow in every part of the world where science is cultivated.
II
Having now considered the more prominent events of Müller's life and his career as a man among men, let us now consider more in detail the nature of Müller's work, its fullness and its limitations. Let us attempt to discover wherein it has proved so substantial a foundation for the later development of modern physiology; and lastly let us make ourselves better acquainted with Müller's strong ​personality, as it was manifested in the home and among the ranks of his students and associates.
In the estimation of a man's prominence it is hardly necessary to remark that the importance which he may assume is always a relative quantity. It is first roughly drawn from a direct comparison of this individual with other individual workers. It is then tempered, as we may say, by a consideration of the relation of the individual activities to the whole field of knowledge existent at that time. There may be great physiologists, great morphologists and great systematists, but the criterion invariably to be used to determine the highest rank must ever be that comprehensive vision which, as Verworn remarks, is able to grasp in a single Weltanschauung, the whole breadth and depth of natural scientific inquiry—that comprehensive analytic and synthetic quality of mind which brings isolated unities of fact into concrete principles. It is from this point of view, and by these standards that we must judge the extent and quality of the work of Johannes Müller: first examine into the relation of his activities to the field of natural science of his day; and, secondly, ascertain the relative value of his work when compared with the labors of other men whom posterity has been accustomed to hold as leaders in the rank and file of natural scientists. And yet, before we can fully understand—much less appreciate—the intrinsic worth of any phase of Müller's many-sided activity, we must first take time to examine briefly the condition of the biological science just previous to the period of Müller's greatest work.
We have already in the course of our discussion made mention of the scope and value of Haller's work in physiology; yet we may be pardoned, perhaps, if, in the present connection, we again make reference to some of the more important characteristics of his period, which extended from 1708 to 1777, and closed something over half a century before Müller's began.
As Galen, in the second century, had shown his recognition of the practical value of physiological data and had laid as a basis of medicine, the practical knowledge of vital phenomena; as Harvey, by his brilliant discovery of the circulation of the blood, temporarily revived, after a sleep of thirteen centuries, the exact experimental method in physiology; and after many other investigators had made important, though isolated, contributions to the budget of physiology, we find Haller bringing together the extensive mass of facts and theories and establishing thereby physiology as an independent science which should pursue not only practical lines for the aid to medicine, but also undertake theoretical aims for their own merit. We find many theories and speculations in the air during the period from 1750 to 1830, the latter date marking the beginning of the period of Müller's greatest activity. As a result of the microscopical observations made in last part of the seventeenth century on the development of the ovum, the theory ​of preformation was attracting wide interest. This had stimulated Caspar Friedrick Wolff to the production of his Theoria Generationis, which was unfortunately held in the dark by the opposition of Haller who could not accept the principles which led, at a somewhat later date, to the conception of Epigenesis. The theory of irritability was also a bone of contention, and though it was materially furthered toward the true conception by Haller's own researches, these last, unfortunately, served also to further a doctrine which thoroughly permeated and confused the development of all physiology down to the middle of the nineteenth century. This was due chiefly to the following fact: That the seeming impossibility of explaining the phenomena of irritability led to the welcoming of the theory of vitalism, or vital force, which asserted a distinct dualism between living and lifeless nature. The vitalists at this time (and nearly all the natural scientists, except perhaps Rudolphi at Berlin, were vitalists in a greater or lesser degree) were discarding the mechanical and chemical explanation of life phenomena, and were introducing such mysterious and inscrutable explanatory principles as la force hypermécanique and the nisus formativus. In this acute and exhaustive manner were explained even the most complex of vital phenomena.
Toward the end of the eighteenth century, however, some twenty years before the birth of Müller, a new note was being sounded from the ranks of German scientists, especially from Reil, whom we may well call the censor of German vitalism. In his work "Ueber die Seelenskraft," he was forcing upon unwilling hearers not only the conception that the life phenomena of living organisms are regulated by chemico-physical laws, but that there were higher principles in control which were present only in living matter. The few adherents to the chemico-physical hypothesis were, during the last years of the eighteenth century, receiving fundamental support from such men as Ritter, Galvani and Humboldt. Through the work of these men the notion was becoming popular that the galvanic current was the cause of all vital phenomena.
Among the chemical and physical discoveries of this time we can mention the advance of vegetable physiology through Ingenhaus (1730-99), who developed the theory of the consumption of carbon dioxide by plants; the discovery of oxygen by Priestley (1733-1804) and Lavoisier (1743-94), and the further discovery in this line by Girtanner, who showed that the venous blood is aerated in the lungs. Thus the existence of the mystical "pneuma," which had clung with a peculiar persistence to centuries of physiological thought, had now become a reality. The anatomical researches of this period were characterized by one discovery in particular, announced by Charles Bell in 1810; that is, the fundamental law of specific nerve physiology, to be later experimentally proved by Johannes Müller. In microscopy, ​Spallanzani, Treviranus and others were dealing what we may call only the first of a long series of death blows to the hydra-headed theory of spontaneous generation, which was not eventually disposed of until the excellent work of Pasteur, over half a century later, and even now is often found lingering in popular scientific lore.
A consideration of these foregoing facts demonstrates to us that the greater number of these exact researches had been carried on in France and England. When now we turn with special interest to Germany, we find that her scientific thought had been fermenting in that powerful intellectual narcotic, the Naturphilosophie, which, under the great influence of Hegel at Heidelberg and Berlin, was stupefying every branch of accurate scientific research throughout Germany. Of the tendency of this movement to avoid the deductive method of research and to build up a conception of nature upon theoretical and speculative conclusions, we shall speak further. For the present, however, having gained some understanding of the condition of natural science, especially physiology, previous to the period of Müller's greatest activity, let us now consider more in detail Müller's relation to these movements, philosophical and otherwise.
Müller, as nearly every other investigator of his time, was a vitalist; but, as Verworn has said, "Müller's vitalism had an acceptable form." Although to him vital force was different from the forces of lifeless nature, its administration nevertheless followed certain physico-chemical laws. In this, Müller's conception seems to be modeled after the idea of Reil, the leader, as we have said, of the most rational form of the doctrine of vitalism in Germany. Müller maintained his position as a vitalist to the very end. He cherished to the last the thought of the existence of a "life energy." We well know how the activity of his pupils has apparently disproved forever this conception for natural science; and how it has led to the opposite extreme, the rather one-sided materialism of the present day.
When we turn to consider Müller's relation to the Natarphilosophie, we recall how he contracted this spirit while he was at Bonn, and how he was rescued, at least from its extreme influences, by Rudolphi at Berlin. Throughout his Berlin period, Müller devoted much of his thought to freeing natural science from the influence of the Naturphilosophie. The result was that not long after the death of Hegel, in 1831, the dangerous play with mystical words became gradually eliminated from the consideration of life phenomena. From this time on, the problems of living substance were furthered, especially by Müller, with the implements of comparative anatomy, of physics and of chemistry. In bringing about this condition, and in establishing the deductive scientific method as alone admissible in the realm of natural science, we must look upon Müller as a reformer whose work has been of enduring benefit to science. The nature of ​his vitalistic hypothesis did not prevent him in the least from directing his labor to establish life phenomena on a physico-chemical basis. Even the vitalistic principle, as it appertains to the philosophy of the present day, is largely a matter of man's personal and ultimate view of his own life and his own destiny.
In our consideration of the relation of Müller's thought to the Naturphilosophie of his time, we must not deny the fact that Müller did recognize a grain of truth in the general philosophic tendencies of that day. As Verworn says: "While keeping constantly in mind the large problems and the goal of science, he regarded critically the special methods and questions only as means to an end—as means for arriving at a harmonious conception of nature." Throughout his whole life he remained steadfastly true to this philosophical conception of science which he had set forth in his inaugural address, "Concerning the Need of Physiology for a Philosophic Consideration of Nature." Verworn further laments that modern science has now so largely lost this element of philosophy, which it had gained as a result of Müller's treatment.
Having dealt thus far with the more abstract phase of Müller's activity and thought, let us now consider more concretely, for a few moments, first the extent of the realm over which Müller exercised so marvelous a command.
When we examine the list of 260 and more complete publications which have come from Müller's pen, we are better able to comprehend the universality of his activities; and it must be understood in this connection that in this great number there are few which represent merely a superficial dalliance with a possible line of investigation. They demonstrate, in almost every case, that Müller plunged boldly into the very heart of the matter which at the time received his fullest consideration. The main subjects to which his contributions appertain, include the following:
| 1. | The Physiology of Motion. |
| 2. | The Life of the Fœtus |
| 3. | The Sense Organs. |
| 4. | Dissection of Invertebrates; also |
| | (a) their development |
| | (b) the histology of their tissues. |
| 5. | Nerve Physiology. |
| 6. | Animal Chemistry. |
| 7. | Human Anatomy. |
| 8. | Ethnography. |
| 9. | Comparative Anatomy of Vertebrates. |
| 10. | Physiology of the Voice and Speech. |
| 11. | Pathological Anatomy. |
| 12. | Systematic Zoology. |
| 13. | Paleontology. |
It is clear that such an extent and variety of undertakings could not result from a single line of investigation, but required a universal activity which it is safe to say has never been equaled by any ​investigator since Müller's time. A better conception of the degree of this extraordinary activity may be gained when one considers that Müller, from 1821 (when he was nineteen years old) to the time of his death, thirty-seven years later, produced, year in and year out, an average of one scientific article of from three to five pages, and with from one to three plates, every three weeks. And in none of these do we find the spirit of his work dictated by the desire to show that he could get some sort of a result out of this or that kind of investigation; but rather by the burning desire to survey and to understand the interrelation of all life phenomena.
It would seem that an unconquered field of knowledge left him no rest, and was for him a stimulus to activity just as much as was the knowledge of the existence of an unconquered people to Alexander the Great. At the first opportunity his attention would be directed to it, and never would the field be abandoned until its truths and its principles were at last incorporated in Müller's own system. This, for Müller, meant no simple undertaking. It included the universal proof, the definite transformation, the deepening, the enriching, the building up and the ordering of every detail of the work; so that from each such acquisition the greatest value to science invariably resulted.
This capability of Müller's is shown especially well in his work on the Echinoderms. He early applied himself to the study of the structure and habits of a single group of this interesting branch of animals. From this study he was led to consider the embryonic development, and, finally, having pursued his investigations in this line into four of the five orders of true Echinoderms, he culminated this great work by subjecting the organization of the entire class of Echinoderms, both recent and fossil, to a thorough revision. In this same thorough and exhausting manner, Müller attacked all possible points in the illimitable field of anatomical and physiological knowledge; and the insight into nature, gained through his own exhaustive researches, yielded to him a sureness of judgment which seldom failed him in the decisive moments of his career. An accurate personal knowledge lay at the bottom of his every work.
In the period of his greatest activity, when he was working simultaneously upon "The Development of the Reproductive Organs," "The Development of the Glands," and also the first volume of his "Handbook of Physiology," together with papers on "Osteology" and "The Myology of the Myxinoid Fishes," he must have possessed the ability to profitably divide his interest and to oscillate with a remarkable ease between these several objects of thought and investigation. The result is perhaps still more marvelous when we realize that, as a rule, Müller went over the same line of investigation three times: the second time while he was writing his results, and the third time when ​the article was in the hands of the printer. Müller's manuscripts are said to have been the "terror" of all typesetters.
There was one peculiarity of this man of genius which, though perhaps a fault, no doubt favored the high degree of productiveness which Müller manifested throughout his life. This was his indifference to the formal completion of his written works. At the culmination of a certain line of investigation, in which he had arrived at definite, and usually important, results, he found too attractive the conclusions and speculations dependent upon these results, to spend his precious moments preparing or finishing his manuscript for the general reader.
Although Müller took, in the earlier part of his life, a certain interest in art, literature and music, it was usually the practical alone which was of consequence to him; and if this phase of the subject were once assured, he went forward in his work without much regard for the polishing or the agreeable rounding-off of his subject. And yet, had Müller lived under different influences and if he had dedicated to the superficial side of his work the same carefulness, we are bound to say that, like Cuvier, he too would have been a master of scientific style. But in spite of this tendency, in what Müller did write he was usually most thoughtful of the manner of his expression. He would sometimes read to members of his department, without disclosing the object, descriptions of certain forms to see whether or not he could awaken in his hearers the conception which it was his desire to implant. He was accustomed to enhance the value of his descriptions by forceful comparisons wherein the wealth of his imagination is readily recognizable. The dredging apparatus which worked before his laboratory window, the hood-like cap of Frau Martha, the little dagger of Cornelius, the sketch of Faust—all these common objects of his sight while hanging on the walls of his study were employed, as much else, for the elucidating of certain phases of the problems which occupied him at the time.
When we come to consider the nature and actual value of Müller's scientific work, it appears that in general he has more developed the principles set in motion by others, than himself given to the world epoch-making discoveries. In his teachings of the glands, of the voice, of the sense of sight and of the tumors, he has, with a tremendous power of work, heaped up an amount of raw material which not only became united in his own system, but has furnished a basis for much of the work in physiology since his time. It was Müller who first clearly recognized the interrelation of psychology and physiology. We remember that in his doctor's thesis he defended the position: "Psychology is nothing without physiology." In this regard Müller's own investigations, wherein he formulated his doctrine of the specific energy of the sense organs, demonstrated how fully dependent psychology might be upon physiology—a conception which in more recent times ​has been developed so far as to arouse in many the belief that psychology should be taught as but a branch of physiology. That Müller saw so clearly the interrelation of these two branches of knowledge is decidedly a point in his favor. His theories were upheld, moreover, by the many facts presented in his works, "Concerning the Comparative Physiology of the Sense of Sight in Man and the Lower Animals," "Regarding the Phantasmal Phenomena of Vision," also "Concerning the Life of the Soul"; and many other references in his "Handbook of Physiology."
Another, and perhaps the greatest, debt which the world of science to-day owes to Müller is for his establishment of physiology upon a comparative basis. This conception did not first arise in Müller, however, but was previously expressed by his teacher, Rudolphi, who had already emphasized the motto: Comparative anatomy is the surest support of physiology. Grasping the fuller significance of this thought, Müller worked throughout his life to uphold the view that physiology can be only comparative; and among the vast number of his physiological works, there are few in which this comparative principle is not more or less clearly expressed.
A further consideration of the nature of Müller's work shows to us the evident necessity of making one concession; and yet one which, under careful examination, may not, after all, detract from the fame which the world accords to him. This is the fact that in spite of his varied activities Müller was never able to make what we may call a scientific discovery of the first rank. We can find issuing from his hand no single observation which, as has often been the case with other so-called great natural scientists, carries down with it through the ages the name of the fortunate discoverer. With the names of Priestley and Lavoisier will ever be linked the discovery of oxygen. The mention of the name Harvey immediately brings to mind the thought of the circulation of the blood, as with the name of Newton we invariably associate the statements of the laws of gravity. But discoveries of equal or even lesser importance can never distinguish the name of Johannes Müller. Even his excellent work on reflex action and the function of the anterior and posterior spinal nerve roots—these do not belong to him alone, for Charles Bell some years before had already promulgated the theoretical law; yet it remained for Müller to prove this law, and by nice experimentation to establish its universal application as a fact. Schwann presented to the world of science that noteworthy discovery that the animal tissue, just as plant organization, is composed of elemental cells; but it remained for Müller to show the highest importance attaching to this discovery, and to lay down the law of the correspondence between embryonic and pathological development.
​This failure of Müller's to make a discovery of the first order can not, with justice, however, be made to count against him. As DuBois Reymond has said, "The most important discoveries can, and often do, play into the hands of insignificant investigators." "That Müller has no such discovery to his credit," continues DuBois Reymond, "can be called as little a failure as that a merchant, who becomes rich through industry and perseverance, should never have been visited by a great fortune." If, in the time when his productive strength stood at its maximum, instead of loosing his great power against a group of widely-extended activities, Müller had undertaken a course in a single definite direction, according to the view of Schiller, that strong stimulus would have been lost to the development of physiology.
Like Müller, Haller also, though he manifested an all-comprehensive knowledge of the field of physiology, failed in yielding an epoch-making discovery. Between these two men, as we have already noted, many points of similarity exist. But, notwithstanding the immense value which Haller rendered to science by his collection and ordering of the tag-ends of physiology up to his time (1775), his work as a whole is excelled by that of Müller with his over-weighing power of judgment and the massive comprehension which took in the whole realm of biological science. While Haller rendered an immense service by uniting the facts of physiology into a certain order and system, Müller took that system as he found it, worked it over, did away with every vestige of the false Naturphilosophie, deepened by his own exhaustive researches every channel of it, and turned into those channels the fresh spirit of a new physiology of comparative anatomy.
We come now, in closing, to a consideration of Müller's personality. From his father Müller inherited the strong and active body characteristic of the Müller line, which is traceable far back into German history. We can picture him a man of medium height; in his youth somewhat slim and of an elegant appearance; the breadth of his shoulders in good keeping with the well-shaped head, which was always held erect with a certain attitude of determination. Lithographs and photographs, pencil, pen and brush drawings presenting Müller's appearance at different times in life, have been given to the world; but, as one of his biographers has said, no picture could accurately repeat, now the sad, now the illuminating, splendor of that dusky countenance, with the dark locks of hair and brilliantly glowing eyes.
While we know that Müller received his physical characteristics from his father, it was from his mother that he appears to have inherited his mental qualities. Among these we may distinguish chiefly the strongly-developed sense of order and method, and the deep spirit of enterprise and of indefatigable activity. To these were added a thorough knowledge of men, a great gift of observation, a conscientious punctuality, and a firmness of purpose together with a ​knowledge of the appropriate both in speech and in action. In his domestic life Müller appears to have been a true husband and to his son and daughters a good father. His home life was of the pleasantest—at least until the misfortune of ill-health in his later life.
As Müller's work as a whole is most comparable to Haller's, so we can say that his personality must have had much in common with that of Pasteur. In both we see the fine sensitiveness of mind, the same modesty in self-assertion, the same love of simplicity, the tenacity of purpose, the scrupulousness for details and the same religious devotion to the hardest labor: these attributes make up a character not altogether common in the general biography of the older school of natural scientists.
Müller's address was characterized by that stiff formality peculiar to the old school type of German professor; and yet with this he combined the dexterity and activity of the more modern scholar. His conversation was never productive. The constant consideration of the various problems of his activity was usually uppermost in his mind and, although he would talk pleasantly and interestingly of many varied subjects, as art, architecture and music, it was to some phase of his labors that the further discussion of these subjects almost invariably led back. And yet, in the circle of his own family, in a group of personal friends, or on his vacation and outings with his nets and microscopes, he could be the most congenial fellow, entering with enthusiasm into whatever duty, sport or pastime presented. Recreation for its own sake, however, Müller seems never to have desired. Yet in his earlier years at Berlin, he was seldom seen exhausted. In his later life, however, the intense nervous strain under which he worked was a source of much regret to his many friends; and the knowledge of his frequent use of opium and other alkaloids to bring him sleep a deeper source of sorrow to those who knew and loved him best.
As a teacher in the anatomical theater and in the class room, as also a guide of young investigators in the laboratory, Müller possessed an extraordinary ability. And yet, in the beginning he had no natural gift of speaking, no eloquence and no talent for foreign languages. Indeed, his early years as academic lecturer at the University of Bonn were, in this particular respect, not in the least promising. With constant practise, however, he was later able to develop a clearness in speaking, and a straightforwardness of expression, which, in itself, approximated to the gifts of eloquence, so that at Berlin he was considered one of the best of university lecturers. His delivery was never of the demonstrative sort, which held an audience spellbound by its bubbling vivacity, its ravishing fire of words, or through a kaleidoscopic blending of current witticism with scientific truth. He never went rambling in a lecture, either in thought or in person. His ​delivery was usually cold and calculating; and yet in some moments he could arouse, through his own deep earnestness, the highest enthusiasm among his students for the subject whereof he spoke—an enthusiasm, the fruits of which have been well shown by the works of the many students, afterwards famous, who received their first impetus from contact with Müller during his periods at Bonn and at Berlin.
In this regard, it is almost needless to say that Müller's position in Berlin resulted in a powerful influence over the younger natural scientists, especially in the northern part of Germany. His personality, as we have seen it, was one to attract students and to hold them when once they knew him well. He planned for them, and often accompanied them on many student trips throughout Germany and even into Norway and Sweden for the purpose of extending various phases of their biological study. In spite of his apparent coldness and constraint, he was, as DuBois Reymond has said, always a ready "comerade," and his views, his books, his apparatus of all kinds, were ever willingly shared with all who desired them.
To the same degree in which Müller was independent in his thought and work, he desired this quality in his students. In his relations with them, notwithstanding his thorough friendliness, it appears that in the laboratories Müller would seldom enter into an ordinary conversation. Regarding this point, DuBois Reymond says in his "Gedächtnissrede," "The greatest reward for us students was when Müller relaxed and spoke in common conversation along the lines of highest pleasantry." Even before his fame as a leader in the field of natural science had gone abroad, and while dependent upon his worth as a teacher alone, he had constantly at his side a circle of eager students who clung to him with enthusiasm. Gathered about him in the earlier days at the University of Bonn, before he went to Berlin, one finds such men as Claparède, Haeckel, Lachmann, Lieberkuhn, Anton Schneider and Max Schultze. Upon his departure to Berlin in 1833, many of his students of the Bonn period followed him, and one need only mention the names of Haeckel, Ludwig, Bischoff, Schultze, Volkmann, Brücke, Helmholtz, Virchow and DuBois Reymond, to indicate the immeasurable significance which, as a teacher and leader of the young investigators of that time, Müller must have exercised. The lines of work which he established, his disciples and followers have carried out, and to what extent, we all realize—not as royal inheritors of that vast sovereign power of their master, but, we may say, as governors over the smaller territories into which, like the empire of Alexander, the field of natural science became divided after the death of its last great ruler. Of this famous group of students, now Haeckel alone remains, DuBois Reymond having died in 1896. Yet all these men, at some period of their lives, have rendered grateful ​testimony to that common source of their first stimulus and earliest enthusiasm, Johannes Müller.
Look as we will through the history of natural science, we do not find an instance where a single individual, gathering about himself a body of select disciples, has by the infusion of his spirit of work sent abroad influences that have ruled so large a part of the territory of natural science. No such influence emanated from Haller, busily engaged in his collections and accumulation of the facts and theories of a century of physiological activity. Nor could it come from Cuvier, excluding from his circle of labor, as he did, the whole field of physiology and embryology, and preoccupied with his foibles of nobility. Nor was such influence from Darwin, secreted in the recesses of his study, modestly content to think, but not to speak. Nor from the combative Huxley, ever at the cannon's mouth with his evolutionary arguments. Nor yet from our more familiar Agassiz, with his noble retinue of followers, and a leader in our own popular thought of natural history though he was. These men have, it is true, been pillars in the development of the biological structure of the present time; yet their fields of labor have been most limited. But it was the nature of the case that it must be so, for no human individual, coming after Müller, could have the same grasp on the ever-extending realm of biological knowledge. Since his time there are few who have become masters of even a single territory.
In these days, when the scientific spirit is throwing its ever-increasing impetus into all lines of human activity, man has little opportunity to look back "to the mountains whence cometh his strength." The source of his to-day's blessings is either wholly overlooked, or, upon special occasions and anniversaries, is (with that feeling which Macaulay has called the "furor biographicus") made to glow in the colors of the sunset. Having avoided, as it is hoped, both of these extremes, we may quickly summarize what, for Johannes Müller, must ever stand as the criterion of greatness: With an all-including glance he was a master of the whole realm of natural science, which he widened until it became too great for its own government. With the certain power of genius, he studied the field of physiology, cleared away the rubbish, breathed into the earth his own spirit, and, in the end, left in the hands of his followers the thrifty seedling of modern comparative physiology, nurtured in the soil of an exact natural scientific method for the investigation of all life phenomena.