Thomas, Karl

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(b. Freiburg im Breisgau, Germany, 28 November 1883; d. Göttingen, Germany, 6 September 1969)

physiological chemistry.

Thomas’s father, Ludwig, was professor of internal medicine and pediatrics at the University of Freiburg; as a youth he met his father’s associates, and almost from the beginning he planned to attend medical school. In 1896, when Ludwig Zehnder, an associate of Wilhelm Röntgen, gave a lecture on the newly discovered X rays at Freiburg, father and son were in attendance. Zehnder asked Karl to stand before a screen, on which he saw the beating of his own heart. On another occasion his father introduced him to Eugen Baumann, who soon afterward detected the presence of iodine in the thyroid gland. Iodine therapy as a substitute for surgery was a frequent topic of discussion in the home.

As a medical student at Freiburg, Thomas attended the chemistry lectures of Heinrich Kiliani and Ludwig Gatterman even though chemistry was not a part of the medical curriculum at that time. Although he completed the medical requirements in 1906, Thomas’s objectives were deflected from medical practice and toward the physiological and chemical side of medical research. As a senior in medicine he completed a thesis titled “Urobilinogen, seine klinische Bedeutung, seine chemische Eigenschaften und seine Farbenreaktionen,” using the Hellige colorimeter developed by his teacher of analytical chemistry, Johann von Autenrieth.

Soon thereafter Thomas joined the Hygiene Institute of the University of Berlin, where he worked under Max Rubner on nutritional problems, particularly the metabolism of nitrogen. By experimenting on himself, he sought to determine the minimal intake of nitrogen necessary for satisfactory health. His methodology was followed in other laboratories where work was being done on nitrogen balance; H.H. Mitchell at the University of Illionois pursued such work, adapting Thomas’s methods to rats. Thomas soon realized, however, that the problem of nitrogen balance was more subtle than comparing protein intake with nitrogen elimination. The structure of the amino acids provide by specific proteins was of greater significance.

Thomas had to abandon laboratory work in 1910 in order to complete his compulsory year of military service by working in a medical unit. He then asked Rubner for a two-year leave of absence to study chemistry at Tübingen, where he was soon made an assistant to Hans Thierfelder and studied the amino acids in blood plasma proteins. Upon returning to Rubner’s laboratory in Berlin (1913), he was placed in charge of the Institute for Work Physiology, an appendage of the recently created Kaiser Wilhelm Society. By the time Thomas’s carefully planned laboratory was completed in 1914, Germany was at war and Thomas left to serve as an army physician. His military service ended late in 1915, after he was seriously wounded. A year later he was sufficiently recovered to resume research at the institute, but his work has hampered by the instabilities associated with Germany’s loss of the war, the subsequent political unrest, and the monetary inflation that followed.

Thomas accepted an invitation to become professor of physiological chemistry at the University of Leipzig in 1921, spending more than two fruitful decades there. During the period he declined attractive offers from Freiburg and Basel. A grateful Saxon government showed its appreciation by building a fine new laboratory that was completed according to his plans in 1939. Very soon thereafter Germany was at war, and the laboratory was forced to undertake research relevant to the war effort. Thomas chose to study the nutritive value of the synthetic fats being produced from coal to supplement the shortage of natural food fats. Considerable progress had been made in the research before the laboratory was destroyed during a bombing raid in 1943.

When the war ended, American troops removed Thomas and some of his associates to the West when Saxony was turned over to the Soviet occupation forces in accord with the Potsdam Agreement. In 1946 Thomas became director of the Institute for Physiological Chemistry in Erlangen, but in 1948 he moved to Göttingen to become director of the Medical Research Institute set up there by the Kaiser Wilhelm Society. Although he retired as director in 1958, at age seventy-five, for another ten years he continued his research there as leader of the group working on silicosis.

Thomas’s leadership qualities are exemplified by the fact that he built up facilities and staff at laboratories in Berlin, Leipzig, and Göttingen despite financial, political, and military obstacles. Much of his career was plagued with personal financial problems, but through simple living he managed to pursue his scientific objectives. He never married but had strong relationships with his scientific associates. He was noted for a rich sense of humor that helped him face many obstacles. Although not sympathetic of the Nazi movement, he managed to survive because of his apolitical stance.

Thomas’s early work on nitrogen metabolism, and later on metabolism of fatty substances, was clearly influenced by the work of Franz Knoop, who clarified the pathway of fatty acid breakdown in his concept of beta-oxidation and further recognized the conversion of keto acids into optically active amino acids. Thomas utilized Knoop’s practice of labeling organic acids (as fatty acids with terminal phenyl groups) to study metabolic changes. He made effective use of methyl groups in studying the breakdown of amino and fatty acids and, after his former student Rudolf Schoenheimer developed the technique of labeling metabolic compounds with isotopic markers, was a pioneer in the use of radioactive tracers in research.

When Thomas chose to study the metabolism of synthetic fats during World War II, he was utilizing research tools he had been developing throughout his career. The fats being synthesized from coal contained all of the fatty acids present in the natural animal fats and vegetable oils but with a difference—they were diluted with fatty acids not normally present in natural glycerides. Whereas food fats normally contain only straight-chain acids with an even number of carbon atoms, the synthetic fats contained not only straight-chain acids with an uneven number of carbon atoms but also acids with branched chains, particularly with methyl groups.

Early feeding experiments with dogs revealed that the synthetic fats were absorbed to a significant degree and, therefore, available as a source of calories. It was also observed that the fatty acids were not oxidized completely, and some strange residues appeared in the urine. Dicarboxylic acids of chain length C6 to C10 were identified, but the bulk of the oily residue defied characterization. A problem appeared in the form of methylated acids, compounds considered not normally present in normal fats. However, study of the preen glands of birds showed the wax to be rich in such compounds. With the reutrn to peace, coupled with destruction of the laboratory, the urgency of such research was lost and Thomas’s later research was concentrated primarily on silicosis.

Although Thomas was strongly motivated toward research, he did not neglect basic teaching, and felt that research and teaching constituted the dual responsibility of a university professor. While at Leipzig he organized a program in which medical school graduates might spend tow years developing their research talents as an adjunct to their medical work.


I. Original Works. See Poggendorff, VI, 2649, and VIIa (pt. 5), 670–671, for listings of Thomas’s periodical publications. He wrote an autobiographical piece, “Fifty Years of Biochemistry in Germany”, in Annual Review of Biochemistry, 23 (1954), 1–16, which covers much of his own career and includes a selected list of more than fifty principal publication by various authors, arranged according to subject area.

II. Secondary Literature. Ernst Schutte, “Karl Thomas zum 80. Geburtstag,” in Die Naturwissenschaften, 50 (1963), 701–702, Also see the following obituaries: Chemischer Zeitung, 93 (1969), 788–789; Hans Fisher, in Journal of Nutrition, 101 (1971), 1109–1115; and Günther Weitzel, in Hoppe-Seyler’s Zeitschrift für physiologische Chemie, 351 (1970), 1–14, Both Fisher and Weitzel include bibliographies.

Aaron J. Ihde

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Thomas, Karl

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