Ludwig, Carl Friedrich Wilhelm

(b Witzenhausen, Germany, 29 December 1816; d. Leipzig, Germany, 27 April 1895)

physiology.

Ludwig’s father, Friedrich Ludwig, was a cavalry officer during the Napoleonic wars, who in 1816 retired from his military post and entered the civil service of the Electorate of Hessen as a Landrezeptor at Witzenhausen; he was promoted to Rentmeister in 1821, and in 1825 moved to Hanau. Lud wig completed his schooling at the Hanau Gymnasium in 1834, then enrolled as a medical student at the University of Marburg, where he was a stormy petrel among his fellow-students. (A deep scar on his upper lip bore witness in later years to his youthful turbulence and dueling.) He was compelled lo leave the university because of conflicts with its authorities, possibly a result of his political activities. After studying at Erlangen and at the surgical school in Bamberg was allowed to return to Marburg. He received medical degree in 1840 and the following year became prosector of anatomy under his friend Ludwig Fick. In 1842 he obtained the venia legendi, the right to teach in the medical faculty, with a dissertation on the mechanism of renal function.

In 1846 Ludwig was appointed associate professor (extraordinarius) at Marburg, where he continued his teaching and research until 1849, when he received an appointment as professor of anatomy and physiology at Zurich. Although most of his time was taken up with dissections and lectures, he continued the investigations of the physiology of secretion that he had initiated earlier, and showed that the secretion of the salivary glands is dependent on nerve stimulation and not on the blood supply (1850). During this time he was also working on his Lehrbuch der Physiologie,, of which the first volume appeared in 1852 and the second in 1856.

In 1855 Ludwig went to Vienna as professor of anatomy and physiology at the Josephinum, the Austrian military-medical academy, which had been organized the preceding year. At this institution he carried on the work that he had begun in Marburg and Zurich, particularly his investigations of the blood gases. In 1859, in a paper published by his student I. M. Sechenov, he described his invention of the mercurial blood pump. This instrument enabled him to separate the gases from a given quantity of blood taken directly in vivo. Over the next three decades, Ludwig and his students, who were growing in number, developed these early researches in a variety of directions, eventually embracing the entire subject of respiratory’ exchange.

When the new chair of physiology was instituted at Leipzig in 1865, Ludwig was offered the post and accepted it. His first problem was the planning of a physiological institute, and he created a model for others to follow. It is probable that Liebig’s chemical laboratory at Giessen and Bunsen’s physical laboratory at Marburg served as examples, Ludwig’s institute, however, was organized in keeping with his broad concept of physiology. He sought to explain vital phenomena in terms of mechanics, that is, through laws of physics and chemistry. It is clear that a visit to Berlin in 1847, in the course of which he met Helmholtz, Brficke, and du Bois-Reymond—men who were to be his lifelong friends and companions in the creation of modern physiology—was influential in the development of his thought.

Ludwig hoped to elucidate physiological problems by combining the study of the anatomy of an organ with a knowledge of the phystcochemical changes that occur in its functioning. To this end he created physical, chemical, and anatomical (including histology) divisions in his laboratory, which was built in the form of a capital “E” One wing was devoted to histology, another to physiological chemistry, and the third, main section was equipped for the physical study of physiological problems.

When Ludwig began his career, there was an almost complete lack not only of physiological laboratories but also of experimental instruments. The circum-stances under which he worked, particularly in his earlier years, fixed the direction of his ideas and methods. He was both an anatomist and a student of physics, conversant with the newest methods and developments of his science. Bunsen was his intimate friend and influenced him greatly in regard to chemistry and physics. Ludwig’s combination of ingenuity, resourcefulness, and knowledge of physical science enabled him to become one of the greatest experimenters in the history of physiology.

In designing the experiments, Ludwig invented numerous methods and instruments. In 1846, he described the kymograph, which, in its subsequent modification by Marey and Chauveau, became a standard tool for the graphic recording of experimental results. His work on circulation led him to devise the mercurial blood pump (1859), the stream gauge (1867), and the method of maintaining circulation in isolated organs (1865).

Ludwig’s teaching was as important as his research achievements. The entire work of the institute was characterized by its complete unity of purpose, a quality well illustrated by his lectures. They were usually given at four in the afternoon, and were addressed to the mature student; all those working under Ludwig’s direction at the institute attended them, and the undergraduates often had a difficult time (most of them heard the lectures several semesters before being examined). Ludwig attacked his lectures in the same thorough, enthusiastic manner that characterized all his work. The focal point was the illustrative experiments, often the result of recent work done in the laboratory, which Ludwig prepared each day, assisted only by his laboratory aide, Salvenmoser,

The spirit of the laboratory was compounded of equal shares of hard work and enthusiasm and the students sensed it immediately. Ludwig’s capacity to judge the abilities of his students led to a useful division of labor. He found something for each worker to do, and he collaborated in the experimentation as well as in the publication of the final results. His role as a teacher was enhanced still further by his Lehrbuch, the first modern text on physiology. The book was meant for students and made no attempt to define life or to elucidate “vital forces” or “biological principles,” In accordance with Ludwig’s basic approach, all explanations of living processes were given in terms of physics and chemistry and the research results that he presented bore testimony to his use of the methods of these sciences.

Ludwig’s desire to investigate and to explain vital processes in physicochemical terms was apparent as early as 1842 in his Marburg dissertation (published the following year as Beitrage zur Lehre vom Mechanismus der Harnsekretion). In it Ludwig developed a physical theory of renal secretion, suggested to him by the structure of the kidney glomeruli, whereby the first stage in renal excretion represented a diffusion of liquid through a membrane because of a difference in pressure between the two sides. He sought to support this theory in further experiments published in 1849 and 1856; these researches are fundamental to present knowledge of diffusion through membranes. In 1851 Ludwig discovered through another series of experiments that salivary secretion depends on initiation by the glandular nerves, the pressure of the secretion being independent of the blood pressure.

Ludwig was interested, too, in all the aspects of circulation. He studied the fluidity of the circulating blood and its lateral pressure, as well as the dependence of these functions on cardiac activity, on the muscles, and on various other factors. He investigated the physiology of respiration, including gas exchange in the lungs, the respiratory movements, and tissue respiration. He also worked on the lymphatic system, making quantitative as well as histological determinations. His treatise on the structure of the kidneys is a classic, and a large part of what is now known about the mechanism of cardiac activity is based upon his work.

Ludwig belonged to that remarkable group of German physiologists and teachers who in the latter half of the nineteenth century created modern physiology. In 1874, on the twenty-fifth anniversary of his professorship, students who had worked with him at Marburg, Zurich, Vienna, and Leipzig presented him with a distinguished collection of original papers. On his seventieth birthday, in 1886, a second Festgabe was presented to him by former students. At the time of his death, almost every physiologist who was active had at some juncture studied with him.

In 1849 Ludwig married Christiane Endemann, the daughter of a Marburg law professor. They had two children, one of whom, a daughter, survived him, as did his wife. He died at the age of seventy-nine, having been ill with bronchitis for seven weeks.

BIBLIOGRAPHY

I. Original Works. For an understanding of Ludwig’s work, see Lehrbuch der Physiologie des Menschen, 1 (Heidelberg, 1852), II (Heidelberg, 1856). His other publications, including those of his students, are listed in Heinz Schroer, Carl Ludwig, Begrunder der messenden Experimentalphysiologie 1816-1895 (Stuttgart, 1967), 294-312, which also contains a number of Ludwig’s letters. For the correspondence between Ludwig and du Bois-Reymond, see Estelle du Bois-Reymond, ed., Zwei Grosse Naturforcher des 19. Jahrunders. Ein Briefweehsel zwischen Emil Du Bois-Reymond und Carl Ludwig (Leipzig, 1927), with foreword and annotations by Paul Diepgen; other letters are include Bernard and Johannes Muller an Karl Ludwin,” Claude Bernard and Johannes Muller an Karl Ludwig,“in Medizinische Klinik, 40 (1925), 1517.

II. Secondary Literature. For information on Ludwig’ life and work, see T.N.Bonner, American Doctors and German Universities (Lincoln, Nebraska, 1963), 120-129; J.Burdon-Sanderson, “Carl Friedrich Wilhelm Ludwig,” in Proceedings. Royal Society of London,59 pt. 2 (1896-1896), 1-8; Simon Flexner and James Thomas Flexner, William Henry Welch and the Heroic Age of American Medicine (New York, 1941), 84 ff; Morton H.Frank and Joyce J.Weiss, “The Introducion’ to Carl Ludwig’ Textbook of Human Physiology,” in Medical History, 10 (1966), 76-86; Wilhelm His, “Carl Ludwig and Karl Thiersch,” in Popular Science Monthly, 52 (1898), 338-353; Hugo Kronecker, “Carl Friedrich Wilhelm ludwigs,” in Berliner lclinische Wochenschrift, 25 (1895), 466 Erna Lesky, “Zu Carl Ludwigs Wiener Zeit, 1855-1865,” Sudhoffs Archive, 46 (1962), 178; and Warren P.Limbard, “The Life and Work of Carl Ludwid,” in Science, 44 (1916), 363-375.

See also N.S.R.Maluf, “Carson, Ludwig, and Donders and the Negative Interpleural Pressure,” in Bulletin of the History of Medicine, 16 (1944), 417-418; “How a Physiologist Anticipates a Physical chemist,” ibid., 14 (1943), 352-365; George Rosen, “Carl Ludwig and His American Students,” ibid., 4 (1936), 609-650; K.E.Rothschuh, “Carl-Ludwig-Portraits in der bilenden Kunst,” in Archiv für Kreislaufforschung, 33 (1960), 33; William Stirling, “Carl Ludwig, Professor of Physiology at the University of Ludwig,” in Science Progress, 4 (1895), 155-176; Robert Tigerstedt, “Karl Ludwig, Denkrede,” in Biographische Bliitter, 1, pt. 3 (1895), 271-279; Gerald B.Webb and Desmond Powell, Henry Sewall, Physiologist and Physician (Baltimore, Md., 1946), 46-50

George Rosen