Part 17

Just after Mueller's promotion to the doctorate in medicine, the Rhenish universities came once more under the authority of the Prussian government, and Berlin became a Mecca for students, who looked upon it in a way as the mother university. After his graduation at Bonn, then, Mueller was attracted to Berlin, and came especially under the influence of Rudolphi, who recognized his talents and gave him special opportunities for original investigation. Rudolphi's private library and his collection were placed at the command of this young original worker, who had already proved his power of investigation and his capacity for following a subject to its ultimate conclusions, even though those were not yet extrinsically known. While at Berlin, too, Mueller came under the influence of the younger Meckel, whom he learned to respect very much. After Meckel's death the _Archives of Physiology_, previously edited by Meckel, fell into Mueller's hands, who successfully continued it for many years.

At Mueller's departure from Berlin he was presented by Rudolphi with an English microscope, as a testimonial of the old professor's appreciation of the young man's labors while under his observation. As Mueller's pecuniary resources were very limited, this must have been an especially acceptable gift, since it enabled him to continue his researches in embryology, and it was not long before these began to bear fruit. At Bonn, to which Mueller returned, he set up as a Privat-Docent in the University, and for several years eked out by teaching the allowance his mother could give him, and even by the practice of medicine.

Bonn, at this time, had a population of perhaps 30,000, {231} and had some eighteen regular practitioners of medicine. It is easy to understand, then, that Mueller's practice did not add materially to his pecuniary resources. It was not long before he gave up the practice of medicine entirely, led to the step by the sad death of a friend, who, while under his care, suffered from perforation of the intestines, followed by peritonitis. Notwithstanding the rather precarious state of his finances, at the age of twenty-six, Mueller married Anna Zeiler, the daughter of a landholder in the Rhineland, not far from Bonn. He had previously dedicated to her a poem, in which he promised her, in lieu of more material advantages as a marriage settlement, an immortal name. The young man seems to have felt something of the genius that was in him, but, then, so have others, and their presages have not always been confirmed by the issue. Shortly before and after his marriage, he applied himself so hard to his investigations of many kinds that within a few months he broke down. The government allowed him a furlough, and for several months he wandered with his bride along the Rhine, in what has been described by a biographer as a "one-horse shay," and came back to his work renewed in mind and body.

As a matter of fact, Mueller's breakdown was what would be called at the present time a neurasthenic attack, induced by overwork and too great introspection. He had been experimenting upon himself in many apparently harmless ways, but by methods which often cause serious trouble. It was not an unusual thing for him to fast, in order to note the physiological effect on his mind and senses of the absence of proper nutrition. He would often lie awake for hours at night in the darkness, experimenting upon himself and noting the phenomena induced, especially in his sight, by the total absence of light. He devoted himself, too, to the investigation of the curiosities of second sight; those interesting {232} reminders of things seen long ago, though without producing much impression, and which recur at unexpected moments, to make us think that we are seeing again when we are really only unconsciously remembering. He used to exercise a good deal the faculty of bringing up objects into his vision with all the physical peculiarities of actual sight. In this his master was Goethe, who had written extensively on this subject in treating of the phenomena of vision, and who was able himself to recall to his imagination with great vividness the many shades of colors of objects with the sensory satisfaction of actual vision. Mueller had this imaginative power only for the reds.

It is not surprising that a young man, engaged too exclusively at this sort of investigation, should have impaired his nervous equilibrium to some degree, and made symptoms, otherwise unimportant, appear to him as the index of serious illness. For a time Mueller despaired of ever being himself again. When he had regained his health, however, he realized what had been the essential cause of his nervous condition; and so he never went back to his introspective observations, considering their results somewhat in the nature of a series of illusions.

After this, Mueller devoted himself for ten years strictly to his physiological investigations. The best knowledge of what Mueller accomplished for scientific medicine, during these early years, can be obtained from Virchow's summation of the discoveries of this period made shortly after his great teacher's death.

Virchow says:

"It was Mueller who introduced to the knowledge of physiologists and physicians the doctrine of reflex actions, which had been already indicated by Prochaska, and simultaneously discovered by Marshall Hall and himself. Just before this Mueller succeeded in showing an {233} easy mode of performing experiments on the anterior and posterior roots of the spinal nerve in corroboration of Bell's teaching of their diverse functions. Thus he had the privilege of establishing for all time two of the greatest practical discoveries of the physiology of the nervous system.

"Next to the nerves the blood became the subject of his researches and he not only naturalized in German medicine the accurate knowledge of the fibrin and blood-corpuscles, which Hewson had cultivated with such fertility in English literature, but he also managed by simple experiment to demonstrate the peculiar composition of the vital fluid. The discernment of right methods of investigation lay ever open to his clear and cultivated intellect, and he knew well that there were cases in which the scalpel and experiments could not determine a question, and where the truth was only to be elicited by means of chemical agents and physical instruments. It was thus he discovered the peculiar gelatinous substance found in cartilage, called chondrin; thus he proved the existence of lymphatic hearts in the amphibia, and thus that he determined not only the organs but all the laws which are concerned in the production of the human voice.

"The special researches of the Bonn epoch are those of the minute structure and anatomy of the glands. They put an end to the controversy which had existed so long between adherents of Malpighi and Ruysch, concerning the sacculated extremities of the glandular follicles, and obtained for us a correct knowledge of these important organs throughout the whole animal kingdom. Perhaps his most important work is that of the Ducts of Mueller, the structures (named after him) which form so important a part of the genito-urinary system in the embryo."

Practically all this had been accomplished before he was {234} quite thirty-two years of age. In the autumn of 1832, Rudolphi, the professor of physiology at Berlin, died. As Virchow says, candidates sprung up on every side, and some who were the least qualified considered themselves best fitted for the position. Mueller took an unusual step which illustrated his decision in character, though in any other it would have seemed an evidence of conceit. He declared, in an open letter, laid before the Minister of Prussia, that his claims were superior to those of any other living physiologist, except John Frederick Meckel. So powerful was the impression produced upon the minister by this letter that he immediately appointed Mueller to the vacant chair.

Not long after his appointment to the chair of physiology at the University of Berlin Mueller completed the well-known "Hand-book of Physiology," which established his reputation. The book is sometimes spoken of as an experimental physiology, but this is not correct. Mueller was no more a mere experimentalist than Haller, and he, himself, heartily detested the tendency which experimental physiology had assumed in France, especially under the influence of Magendie. Part of Mueller's aversion to experimental physiology was aesthetic. He could not bear the idea of inflicting so much pain as many of his colleagues inflicted without a thought. In his panegyric of Rudolphi, Mueller says: "Rudolphi looked upon physiological experiments as having no relation to anatomical accuracy, and it is no wonder that this admirable man, who had at every opportunity expressed his abhorrence of vivisection, took up a hostile position against all hypotheses and conclusions insufficiently established upon physiological experiments." Mueller adds: "We could not have failed to share his righteous indignation, had we seen how many physiologists were using every effort to reduce physiology to an experimental science by the live dissection and agonies {235} of innumerable animals, undertaken without any definite plan, and yielding often only insignificant and imperfect results."

Mueller shared these views of Rudolphi with regard to vivisection. The uncertainty of the conclusions, the amount of suffering inflicted, and the indefiniteness of the conditions of experiment, so that the conclusions could not have any very great weight, or any special accuracy of information, made him consider such experiments, unless very carefully conducted by trained investigators, as largely a waste of time and infliction of unnecessary pain and a leading astray of physiological advance because of the uncertainty involved.

The qualities in Mueller's "Hand-book of Physiology," which gave it its greatest value, are the thorough review of all of the physiological literature of the world which it contains, and the greatest number of original observations it details as the basis of the principles enunciated. Mueller himself said, in the preface to his "Hand-book": "I need scarcely remark that it is the duty of a scholar to make himself acquainted with the progress of science among all nations; and this is now possible and, moreover, quite indispensable in these days of progress. A purely German, French, or English school of medical science is barbarism; and in Germany we would consider the idea of an isolated English or French system of natural history, physiology or medicine just as barbarous as the notion of Prussian, Bavarian, or Austrian medicine or physiology."

How valuable the book was as the corner-stone of modern German medicine, may best be judged from Virchow's opinion of it. He says in his panegyric of Mueller:

"There are two qualities in his 'Hand-book of Physiology' which have particularly enhanced my estimation of its value--its strictly philosophical method and its completeness {236} in facts. Since the time of Haller no one has so thoroughly mastered the entire literature of natural history or collected in all directions so many original experiences, and no one has been at the same time familiar with medical practice, as well as with the remotest provinces of zoology. It has been well said that while Haller often, in doubtful questions, espoused a side which must eventually be forced to succumb, Mueller always had the luck (if we may call that luck which was preceded by so much intelligent activity), sooner or later, to discern the opinion that was sure, eventually, of the victory. He was wonderfully fitted for the office of critic by his comprehensive knowledge. He knew how to discriminate the healthy from the unsound, the essential or real from the adventitious or accidental. And, in surveying the whole series of forms--often widely different--among which a well-determined plan of nature seemed to be realized, he knew the changes which not infrequently altered considerably the arrangement and composition of the substances within these forms. In Mueller, as a physiologist, it is not the genius of the discoverer, nor the ground-breaking nature of his observations we admire, but rather the methodical exactness of investigation in calculating judgment, the confident tranquility and the perfect consummation of his knowledge."

In a word, Mueller owed the success of his career to the perfect poise of his intellect and the admirable critical faculty that guided him in the thorny path of knowledge at a time when there were so few landmarks of real scientific significance to show the investigator what the probable course and progress of real science must be. It was for this reason that, as Virchow has said, the reform of newer views became embodied in him, and in spite of the almost monastical retirement of the scholar, the influence of the method introduced by Mueller was not limited to physiology, but continues to {237} spread beyond that science in ever-widening circles into the domain of all the biological sciences.

Virchow concludes: "Mueller vanquished mysticism and phantasms in the organic kingdom and he was most distinctly opposed to every dangerous tendency, whether it was pursued under the pretext of physiology or belief, or merely in accordance with conjectures. Mueller did not discover, but he firmly established the exact method of investigating natural sciences: Hence, he did not found a school in the sense of dogmas--for he taught none, but only in the sense of methods. The school of natural science which Mueller created knew no community of doctrine, but only of facts and still more of methods."

He did not confine himself in his studies, however, to the physiology and pathology, nor even to the anatomy and embryology of man. After 1840 he devoted himself to the study of invertebrates and investigated the starfish and the pentacrinites. While engaged in his work on the invertebrates he found that the fossil remains of animals had not been carefully explored, so for a time he devoted himself to paleontology. While his salary as professor was ample for his own support, it was not what would be called generous at the present time, yet Mueller became so devoted to his science that he paid certain of the workmen to be on the lookout for fossil remains for him in the quarries of the Eifel. He became deeply interested, too, in life in the sea and made his vacations times of specially hard work, investigating the conditions of low life among marine organisms. He passed from one class of life to another. From sea-urchins and starfish to infusoria and polycystina, whose varieties he was himself the first to recognize and describe.

Mueller was one of the first to point out that certain of the lower animals could propagate similar and dissimilar {238} generations, that is, reproduce by alternate generations. He studied and demonstrated especially the metamorphoses in the echinodermata, and his broad vision and careful observation in this new and surprising scientific field cleared up many things that had been mysteries before.

In paleontology Mueller worked with our own Agassiz, then a young man, or perhaps it should rather be said that Agassiz worked with Mueller. A paper, for whose compilation they made a series of observations together, appeared at Neufchatel, in 1834. It was a note on the vertebrae of living and fossil dog fishes. At this time Mueller was interested in fossil fishes of many kinds and wrote several articles in later years on this subject. Toward the end of Mueller's life he studied especially the polycystina, certain of the radiolaria, and some of the many chambered specimens, fossil and living, that were attracting much attention at that time. As a matter of fact he went the day before his death to the zoological museum of Professor Peters in Berlin, in order to obtain some polythalamacea.

How open to advance in science and how ready to encourage the work of others Mueller was, may be gathered from his attitude to parasites as the cause of disease, when these began to be discovered. After Professor Schoenlien's discovery of the parasite of favus, Mueller became interested in it, confirmed Schoenlein's observations and added something to our knowledge of it. About this time, also, he discovered the psorosperm as a parasite of animals and possibly of man, and devoted considerable attention to it. His work was afterward greatly extended by one of his pupils, Lieberkuehn, whose researches with regard to these minute organisms attracted the attention of the medical world.

It is not a little surprising how many of the investigations that afterward were to give fame to Virchow were initiated {239} by his great teacher, Mueller. It was Mueller whose study of tumors led Virchow to devote himself to this subject and give us the best pathological work on it that has ever been written. Virchow himself notes with regret that Mueller turned aside from pathology and never finished the promised work which was to have contained his theory of the origin of tumors. Another work in which Virchow followed in Mueller's footsteps was the development of craniometry and, in general, the scientific investigations of skulls. Mueller had interested himself very much in microcephalic skulls and Virchow assisted him in the investigations of them. Many years afterward Virchow established the science of craniology in the department of anthropology, and succeeded in throwing not a little light on the origins of races by his discoveries in this matter.

After Schoenlien's discovery of the parasite of favus, Mueller became interested in the parasitology of human beings, and with Retzius, the famous Swedish anatomist, investigated certain molds which occur in the respiratory passages of birds. They succeeded in demonstrating that these vegetable parasitic growths were a form of Aspergillus. Their studies in the white owl particularly called general attention to the possibility of such molds occurring as parasites of animals. Later on, Virchow showed that these same molds occur occasionally in the respiratory passages of men. Virchow found them in three bodies at autopsy, all of them being run down individuals, two of them old subjects, and all sufferers from chronic bronchitis. Usually, when the parasites were found, there was a distinct tendency to very low resistive vitality in the tissues, sometimes proceeding even to the extent of beginning pulmonary gangrene. In reviewing the subject Virchow [Footnote 7] said that the light thrown {240} upon it by the investigations of Mueller and Retzius was of the greatest possible assistance in enabling him to identify the parasite when he found it in human subjects.

[Footnote 7: Virchow's Archiv, Bd. ix.]

The number of positive facts which Mueller brought to light in the most diverse departments of science is almost beyond calculation, and yet it is astonishing how seldom the slightest error, or even an incomplete observation, can be found in his work. On the other hand, it has happened, over and over again, that when the correctness of his observations in the beginning seemed according to other investigators to be dubious, they have come eventually to be acknowledged as representing the truth. As a rule, he went over every set of observations three times. During the second series he wrote about them. He always repeated the experiments on which his observations were founded while his material was going through the press. His manuscripts were a mass of corrections; notwithstanding this, his proof sheets were the despair of the printers.

Mueller accomplished all this only by the most careful husbanding of his time. He knew how to make use even of the ends of hours and brief intervals which others waste without a thought about them. He used to call these periods of short duration between the duties "the gold-dust of time," and said that he did not wish to lose a particle of it. In the quarter of an hour between two lectures it was not an unusual thing to find that he took up some dissection at which he was engaged, or continued his work sketching the observations that he had been making during the previous day.

How thorough was Mueller's work in everything that he devoted himself to can be gathered from certain excursions into pathology, which was, after all, only a side issue in his work, and to which he gave very little serious attention. Mueller's assistant in the Museum of Berlin, and one of his {241} favorite pupils, Schwann, made a series of what Virchow calls comprehensive and magnificent investigations on the cell structures of the animal tissues, on which progress in pathology so essentially depends. Mueller followed up these discoveries, and, to quote Virchow once more, he was in this matter the authority of authorities; for the medical world owes to him practically all its knowledge of tumors. Mueller first demonstrated the harmony which existed between the pathological and the embryonic development of tumors.

This physiological observation is of the highest importance. It came at a time when tumors were considered to have nothing of the physiological about them, but to be entirely manifestations of morbid processes foreign to all natural functions of the body. Mueller's observation of the identity of the pathological and the embryonic development of tumors is really the key to the whole doctrine of morbid formations. Virchow assures us that Mueller's labors gave the strongest impulse to the employment of the microscope in pathological investigations. Undoubtedly this was his most important contribution to scientific medicine. With this he laid the foundation of the explanations of tumors--a work that his great pupil was destined to carry on. Some of Mueller's work in this line, his study of enchondromata for instance, Virchow confesses to have been part of the inspiration that led to his own later work. Mueller was occupied, however, with too many things to devote himself to the study of pathology in the way that would have been necessary to make great discoveries in the science. He promised that he would sometime settle down to make a classification of tumors, and that the principle of such a classification would not be based either on their fineness of structure or on their chemical composition, but that their physiological nature and tendency to grow must be taken into account. When he died, however, he {242} left behind him nothing unfinished except the long-expected conclusion of his book on tumors.

Mueller's most important work in physiology, and his most far-reaching influence on the biological sciences, which were just then beginning their modern development, came from his assertion of vital force as a thing entirely different from and absolutely independent of the physical or chemical forces which it directs and makes use of. Vital force for Mueller was the ultimate cause and supreme ruler of vital phenomena, so that all the energies of an organism follow a definite plan. It was for him the complete explanation of all the physical manifestations of life. It disappears in death without producing any corresponding effect. Without losing anything of itself it hands over in multiplication or reproduction a force equal to itself to the new being that is born from it. This vital force that is thus handed over need not necessarily manifest itself at once, but may lie dormant for a long time to be awakened to manifestations of life by the concurrence of proper conditions in its environment.