Makers of Modern Medicine

by James J. Walsh

Theodore Schwann, the first to formulate the cell doctrine, to promulgate the teaching that all living tissues, whether plant or animal, are composed of a number of minute elements which under all circumstances are biologically equivalent--is the father of modern biology. Cells had been seen and recognized as such before, but their significance was first pointed out by him. His cell theory has now become the [{256}] cell doctrine, the teaching of all the schools of biology. The generalization that forms the basis of the doctrine was the result of some of the most accurate and careful observation that has ever been made. The work was done when the mechanical helps to the analysis of tissues were in the most primitive condition. The microscope had just been introduced into general laboratory work. The microtome, the instrument by which tissues are cut into thin sections suitable for microscopic examination, and to which almost more than to the microscope itself we owe our detailed knowledge of the intimate constitution of tissues, was as yet unthought of. Despite these drawbacks Schwann's work was done with a completeness that leaves very little to be desired. He published, when not yet thirty, the story of his comparative investigation of the cellular constitution of plants and animals, and there is very little that can be added, even in our day, to make its scientific demonstration any clearer than it was. It was typical of the man that, heedless of disputatious controversy over details of his work, he should go calmly on to complete it, and then give it to the world in all its convincing fulness. The same trait crops out with regard to other subjects. His was one of the great scientific minds of the century, always immersed in a philosophic calm befitting the important problems he had in hand. His life is ideal in its utter devotion to science, and to the teaching of science, while no duty that could round it out and make it humanly complete for himself or others was despised or neglected.

Theodore Schwann was the fourth of a family of thirteen children, born in the little German town of Reuss, not far from Cologne. He received his college education in the Jesuit Gymnasium of Cologne, and passed thence to the University of Bonn. The lower Rhineland is largely [{257}] Catholic, and to this day, though Bonn has become the fashionable exclusive German university to which the Kaiser and many of the scions of the great German families go for their higher education, the faculty of theology at the university remains Catholic. Schwann devoted some time here to the study of theology, but he came under the influence of Johann Müller, was allowed to assist in some of his experiments on the functions of the spinal nerves of frogs, and this seems to have determined him to a medical career.

After two years spent in medicine at Würzburg, another great Catholic university of Southern Germany, we find Schwann at the University of Berlin, once more working with Johann Müller, who had been invited from Bonn to fill the distinguished Rudolphi's place in the chair of anatomy at the rising Prussian university. Müller was one of those wonderful men--they turn up, unfortunately, all too rarely--who, though not great discoverers themselves, have the invaluable faculty of inspiring students with an enthusiasm for original observation which leads to the most brilliantly successful researches. A great teacher, in the proper sense of the word, he was not. In his public lectures and his ordinary lessons he was often arid and uninteresting, insisting too much on unrelieved details, "the dry bones of science." He seems to have failed almost completely in conveying the usual scientific information of his course with the air of novelty that attracts the average student. The true teaching faculties are not given to many. Müller had a precious quality all his own that has proved much more valuable for science than the most enlightened pedagogy.

To the chosen few among his students who were drawn into close intimacy with him and permitted to share his personal scientific labors, Müller proved a source of most precious incentive--a suggestive master, the inspiration of [{258}] whose investigating spirit was to be with them throughout life. To no one, except perhaps to Socrates of yore, has it been given to have sit at his feet as pupils so many men who were to leave their marks upon the developing thought of a great era in human progress. Beside Schwann, there studied with Müller, during these years at Berlin, Henle the anatomist, Brücke the physiologist, Virchow the pathologist, Helmholtz the physicist, Du Bois-Reymond the physiologist, Claparède, Reichert, Lachmann, Troschel, Lieberkühn and Remak. All these names are writ large in the scientific history of the century. It is a remarkable group of men, and of them Schwann, with the possible exception of Helmholtz, will be remembered the best by posterity; certainly none of them would not have cheerfully resigned his hopes of scientific renown for any work of his own to have made the discovery which, as an enthusiastic biographer said, set the crown of immortality on a young, unwrinkled forehead.

Schwann's thesis for his doctorate at Berlin showed the calibre of the man, and demonstrated his thorough fitness for success as an experimental scientist. The question whether the growing embryo in the ordinary hen's egg consumes oxygen or not had been in dispute for some time. It was well known that an air-chamber existed in the egg even at the earliest stages of embryonic life. It was understood that the mature chick just before its egress from the egg must have air, and the porosity of the egg-shell was sufficient to permit its entrance. Whether at the beginning of embryonic life within the egg, however, oxygen was necessary, remained somewhat in doubt. It had been demonstrated that the gas existing in the air-chamber of an egg became changed in composition during the progress of development. From being slightly richer in oxygen than ordinary atmospheric air at the beginning of embryonic growth, [{259}] containing 24 to 25 parts of oxygen per 100, it became modified during comparatively early development so as to contain not more than 17 parts of oxygen per 100 and some 7 parts of carbon dioxide. This change of composition was, at least, very suggestive of the alteration that would take place during respiration. It was pointed out, however, that the argument founded on these observations was drawn only from analogy, and was by no means a scientific demonstration of the fact that the embryo not only consumed air during its growth, but actually needed oxygen for the continuance of its vital processes.

It was suggested that the change of composition in the air within the egg might be due not to any essential vital functions, but to chance alterations brought on by decomposition in the unstable organic material so abundantly present in the substance of the egg. Schwann settled the question definitely by a set of ingenious experiments. He exposed eggs for various periods to the action of other gases besides air, and also placed them in the vacuum chamber of an air-pump. When not in contact with the air the eggs developed for some hours if the temperature was favorable, and then development ceased. If after twenty-four hours' exposure to an atmosphere of hydrogen eggs were allowed free contact with the air, development began once more at the point at which it had ceased. After thirty hours of exposure to hydrogen, however, or to the vacuum, all life in the egg was destroyed, and it failed to develop no matter how favorable the conditions in which it was afterward placed. The completeness with which the points in dispute in this problem were demonstrated is typical of all Schwann's work. His conclusions always went farther than the solution of the problem he set out to solve, and were always supported by simple but effective experiments, often ingeniously planned, [{260}] always carried out with a mechanical completeness that made them strikingly demonstrative.

One of Schwann's brothers had been a worker in metal, and Schwann himself had always shown a great interest in mechanical appliances. This hobby stood him in good stead in those days when laboratories did not contain all the intricate scientific apparatus and the facilities for experimentation so common now, with their workshop and skilled mechanics for the execution of designs. Many another worker in the biological sciences of that time owes his reputation to a similar mechanical skill. Experiments were impossible unless the investigator had the mechanical ingenuity to plan and the personal handiness to work out the details of appliances that might be necessary for experiments. It is told of Schwann that when Daguerre's discoveries in photography were announced, such was his interest in the new invention that he made a trip to Paris especially to learn the details of the method. Some daguerreotypes made by him according to the original directions of the inventor himself are still preserved by his family.

Schwann's investigation of the respiration of the embryo in hens' eggs led to further studies of the embryo itself, and to the discovery that it was made up of cells. Later came the resolution of other tissues into cells. When, after his graduation as doctor in medicine, the post of assistant in anatomy at Berlin fell vacant, it was offered by Johann Müller to Schwann. The position did not carry much emolument with it. The salary was ten German thalers--i.e., about $7.50 per month--a pittance even in those days when the purchasing power of money was ever so much greater than now. His duties took up most of his time. The work was congenial, however, and Schwann remained here for five years. As Henle has said in his biographical sketch of [{261}] Schwann, in the Archiv f. mikroskopische Anatomie, just after his death in 1882: "Those were great days. The microscope had just been brought to such a state of perfection that it was available for accurate scientific observations. The mechanics of its manufacture had besides just been simplified to such a degree that its cost was not beyond the means of the enthusiastic student even of limited means. Any day a bit of animal tissue, shaved off with a scalpel or picked to pieces with a pair of needles or the finger-nails, might lead to important ground-breaking discoveries." For at that time almost everything as to the intimate composition of tissues was unknown. Discoveries were lying around loose, so to speak, waiting to be made. Schwann was not idle. The precious years at Berlin saw the discovery that many other tissues were composed of cells. The nuclei of the striped and unstriped muscles were found, and while the cellular character of these tissues was not demonstrated, their secret was more than suspected and hints provided for other workers that led very shortly to Kölliker's and Henle's discovery of muscle cells.

Besides his interest in histology, the branch of anatomy which treats of the intimate constitution of tissues, Schwann was working also at certain general biological questions, and at some knotty problems of physiology. Not long after his installation as an assistant at Berlin, from observations on fermenting and decomposing organic liquids, he came to a conclusion that was far in advance of the science of his day. He announced definitely infusoria non oriuntur generatione aequivoca--the infusoria do not originate by spontaneous generation. Under the term infusoria, at that time, were included all the minute organisms; so that Schwann's announcement was a definite rejection of the doctrine of spontaneous generation over thirty years before Pasteur's demonstrations finally settled the question. Schwann was never a [{262}] controversialist. He took no part in the sometimes bitter discussions that took place on the subject, but having stated his views and the observations that had led up to them he did not ask for the immediate acceptance of his conclusions. He continued his work on other subjects, confident that truth would prevail in the end. When the congratulations poured in on Pasteur for having utterly subverted the doctrine of spontaneous generation, the great French scientist generously referred the pioneer work on this subject to Schwann, and sent felicitations to that effect when Schwann was celebrating the jubilee anniversary of his professoriate.

While studying ferments and fermentations Schwann became interested in certain functions of the human body that carry with them many reminders of the biological processes which are at work in producing the various alcohols and acids of fermentation. The changes that occur in the contents of the human stomach during the preparation of food for absorption had long been a subject of the greatest interest to physiologists. It had been studied too much, however, from the merely chemical side. The necessity for the presence of an acid in the stomach contents in order that digestion should go on led to the conclusion that the acid was the most important constituent of the gastric juice. By means of the scrapings of the stomachs of various animals Schwann succeeded in preparing an artificial gastric juice, and showed just how the action of the gastric secretions brought about the solution of the contents of the stomach. He isolated pepsin, and demonstrated that it resembled very closely in its action the substances known as ferments. He even hinted that digestion, instead of being a chemical was a biological process. Any such explanation as this was scouted by the chemists of the day, headed by Liebig. Most of the physiological functions within the human body were [{263}] then triumphantly claimed as examples of the working of chemical laws.