After Schoenlien's discovery of the parasite of favus, Müller 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 Müller 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 Müller 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.
Müller 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 Müller'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. Müller'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. Müller 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. Müller 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. Müller'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 Müller'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 Müller'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. Müller 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.
Müller'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 Müller 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.
In a word, Müller appreciated fully the mystery of life, faced the problem of it directly, stated it in unequivocal terms, and by so doing saved the rising science of biology from wandering off into speculations which were seductive enough at that time, but which would have proved vain and wasteful of time and investigative energy. Müller's influence on his students was sufficient in this matter to set the seal of vitalism, as it is called, on most of the biological work done in Germany about the middle of the century, and it was a recurrence to his observations and his methods which led the reaction to vitalistic theories that characterized the concluding years of the nineteenth century.
With regard to the significance of Müller's work, Professor Du Bois-Reymond, himself a pupil of Müller, in his memorial [{243}] address delivered before the Royal Academy of Sciences of Berlin in 1859, [Footnote 8] says: "It has been objected by those who insist on the greatness of Müller's reputation that he himself made no discovery that can be said to be of the first rank. Müller's fame is great enough for us to allow that there is something true in this objection. He accomplished more in developing the ideas of others than in original research of his own. That he did not make any great discovery is, however, rather due to the fact that he came at a time when great discoveries were no longer lying around loose as they had been in the preceding century, waiting to be made, as it were; and what he accomplished was of more value than one or two single discoveries of primary importance. He made the original ideas of other men so clear that they were at once accepted by all the medical and scientific world. In this way he furthered the progress of medicine better than any devotion, however successful, to one single feature could possibly have accomplished.
[Footnote 8: Gedächtnissrede auf Johannes Müller, von Emil Du Bois-Reymond, Berlin, Buckdruckerei der Königlichen Akademie der Wissenschaften (Dummler), 1860.]