(b, Kassel, Germany, 23 August 1781; d. Munich, Germany, 22 January 1861), anatomy, physiology.
Tiedemann was the son of Dietrich Tiedemann, a professor of philosophy, Greek, and classical literature, who took great interest in his son’s early education. He attended the Marburg Gymnasium, then, in 1798, entered the university there to begin medical studies. His chief interest was medical theory, and in 1802 he began to concentrate on theoretical subjects at Bamberg and Würzburg, under the guidance of J. N. Thomann and Kaspar von Siebold; the inability of physicians to prevent his father’s death of a contagious disease in 1803 further strengthened his aversion to practical medicine.
Tiedemann graduated from Marburg with the M. D. in 1804, then remained there to attend Franz Joseph Gall’s courses on physiology, comparative osteology, and craniology. Gall’s exceptionally skillful fine anatomical preparations set an example for Tiedemann’s own later work. Tiedemann then returned to Würzburg to study with Schelling. He was, however, able to resist the seductiveness of Naturphilosophie–Schelling himself was responsible, Tiedemann later wrote, for his decision to remain faithful to the methods of empirical research and observation–and determined to go to Paris to study with Georges Cuvier. In the course of his journey he met S. T. Soemmerring, who was greatly impressed by Tiedemann’s preparation of the nervous system of the pigeon. It was upon Soemmerring’s recommendation that Tiedemann was in 1807 called to the Landshut Medical Faculty as professor of anatomy and zoology.
In Paris, under Cuvier’s tutelage, Tiedemann became interested in comparative anatomy and morphology, and these studies formed the basis for the first works that he published in Landshut. Among these were three sections of a projected, but never completed, textbook on zoology. Three parts were brought out (in 1808, 1810, and 1814, respectively); of these the first dealt with problems of general zoology, and in particular the classification of mammals, while the second and third were devoted to birds. The published segments of the work were greeted as the most comprehensive compendium of zoological data since Cuvier’s own Leçons d’anatomie comparée. At the same time, Tiedemann also published a series of monographs summarizing his studies on specific subjects. These included a work on the heart in fish (1809), detailed studies of the anatomy and natural history of the great reptiles (1811 and 1817), and a number of works on the structural anatomy of birds and amphibia, especially the lymphatic vessels and respiratory organs of birds. His 1816 publication on echinoderms (holothurioidea [sea cucumbers], starfish, and sea urchins), a subject set by the Académie des Sciences, won its prize and Tiedemann was elected a corresponding member.
During the same period of his career, Tiedemann did further important research on morphology and embryology. He studied the fetal development of bone tissues and demonstrated beyond doubt that the maternal blood is not transmitted to the fetus, which rather has its own closed circulatory system, separate from (but closely associated with) the maternal one. His most important work in this area lay in his studies of the development of the brain; his Anatomie und Bildungsgeschichte des Gehirns im Fötus der Menschen, nebst einer vergleichenden Darstellung des Hirnbaues in den Thieren, dedicated to J. F. Blumenbach, was published in 1816.
In the preface to this work, Tiedemann stated that, since the fully developed fetal brain had been described exhaustively, it was therefore necessary to study its anatomical development in detail; anatomy, he added, would be a mature science only when the different stages of development and mutual relations of various structures had been examined so that the laws that governed them might be understood. Continuity of observation, Tiedemann stated, was essential, and his book represented the results of several years of continuous research. He was thus able to record the exact stage at which a number of structures first arose in the fetal brain, together with the duration of brain growth and the time of its completion. A comparison of the durable forms of the brain of various animals with the transitory embryonic configurations of the human brain allowed him to draw an analogy between the adult animal brain and the human brain at a certain stage of development; he was also able to detect the crossing of the pyramidal tracts in a very young embryo, the changes in the peripheral nerves, and the cranial shift of the sacral part of the spinal cord. His book contained a number of beautiful and accurate illustrations, and was later translated into French and English.
In 1816 Tiedemann went to the University of Heidelberg to take up an appointment as professor of anatomy, comparative anatomy, physiology, and zoology. The new post offered him greater resources (among other things, there was a more generous supply of cadavers for dissection), and brought him into contact with a younger colleague, the chemist Leopold Gmelin, whose work strongly influenced his own. Tiedemann’s interests gradually became concentrated on problems of physiology, and with Gmelin he performed a considerable body of research, in which he assumed responsibility for animal experimentation and observation, while Gmelin carried out chemical examinations.
In 1820 Tiedemann and Gmelin published Versuche über die Wege auf welchen die Substanzen aus dem Magen und Darm ins Blut gelangen, über die Verrichtung der Milz und über die geheimen Harnwege, an account of their researches on the passage of various substances from the stomach or intestines to the blood, on the function of the spleen, and on the hypothetical hidden urinary ducts. The absorption of nutrients from the alimentary tract had long been of interest to Tiedemann–it had, in fact, motivated his previous studies on the lymphatic vessels–but his work on the spleen was something quite new. The role of the spleen had been hitherto only a subject of speculation; Tiedemann’s attempts to prove experimentally, in horses and dogs, that the spleen secreted a fluid that passed through the lymphatic system to participate in the transformation of chyle into blood served as the basis for all further work on the part of the spleen in blood formation. Tiedemann and Gmelin also showed that the hidden urinary ducts posited by other workers could not exist.
In 1822 Friedrich Sigismund Leuckart assumed responsibility for the teaching of zoology and comparative anatomy at Heidelberg and Tiedemann was able to devote all his time to physiology. The following year the Paris Académie des Sciences announced a prize for the best work encompassing the chemical composition of the digestive juices, the digestion of simple and complex foodstuffs in animals (including mammals, birds, reptiles, amphibians, and fish), the contents of the stomach and intestines during periods of fasting and eating, and the passage of digested substances into the blood, lymph, and urine. Under this stimulus Tiedemann and Gmelin decided to expand their earlier work on digestion into a comprehensive study, using chemical methods as well as experimental and microscopic investigations, designed to satisfy the conditions of the award.
Digestion had been thought of as a single process, taking place in a single organ, the stomach. Tiedemann and Gmelin, however, observed the digestion of foodstuffs as they passed through the alimentary tract and investigated the assimilation of nutrients into the blood and lymph and the eventual elimination of waste products to demonstrate that digestion is in fact a complicated series of processes, involving a number of organs. They proved that for some substances digestion represents not a simple dissolution but rather a chemical transformation, as, for example, displayed by the conversion of starch into glucose. They showed experimentally that the digestive juices have discrete properties, as, for instance, the pancreatic juice, formerly thought to be an abdominal saliva, which they obtained through an experimentally induced abdominal fistula and tested chemically to demonstrate its difference from saliva.
Chief among their other findings was their discovery of a number of biliary substances, of which some (such as pigments) were merely excreted, while others played more important physiological roles, as in the absorption of fat, which diminished when bile was not present. They also (shortly after Prout, but independently and by a different method) detected the presence of hydrochloric acid in the stomach and showed that it increases in quantity with the digestion of certain foods. They further described the color reactions of proteins during pancreatic digestion and discovered glucose, transformed chemically from starch and similar substances, in the blood.
Despite their remarkable achievement, Tiedemann and Gmelin did not win the Académie’s prize. That body decided rather to divide the prize between them and two young French scientists, François Leuret and Jean-Louis Lassaigne, giving each entry half the prize and an honorable mention. Resentful, Tiedemann and Gmelin refused to accept any part of the award and announced that they would submit their work to the judgment of the entire scientific world; their Die Verdauung nach Versuchen was published in Heidelberg in 1826. The great chemist Berzelius characterized the book as “a long series of investigations about the process of digestion, in which everything that anatomy and chemistry could at present offer to its study was used,” and praised it as “uncontestably the most complete physiological examination [of digestion], which has enriched the chemical study of the processes that occur in living animals.” And indeed, further advances in the study of digestion became possible only with advances in chemistry.
By 1835 Tiedemann had begun to suffer from the eye complaint that eventually led to the loss of his sight. In that year he was relieved of his courses by his son-in-law, Theodor Bischoff, although he continued to carry out his own research. In 1836 he published, in English, what may be considered one of the earliest basic works of physical anthropology, On the Brain of the Negro Compared With That of the European and the Orang-Outang. In this surprisingly modern study, Tiedemann showed that, in contrast to the large difference between the forebrains of apes and men, no substantial differences could be found between the brains of the races of men; although the majority of Negro skulls and cranial cavities that he studied were smaller than those of European specimens, they had, by his measurement, contained brains as large and as heavy. He further stated his finding that there was no area of intellectual actvity in which Negroes could not perform as well as European whites, and concluded that there was no natural formation or disposition of the brain in Negroes that would substantiate the notion of their predestined subservient state.
In 1844 Tiedemann took up the task of designing a new anatomical theater. His life was disrupted by the revolution of 1848-1849; not only was he opposed to popular uprisings, for political and philosophical reasons, but also three of his sons were army officers. The eldest, Gustav Nicolaus Tiedemann, was executed under martial law, and the two others had to flee into exile. In 1849 Tiedemann retired from the University of Heidelberg and settled first in Frankfurt am Main, and then, in 1856, in Munich. The fiftieth anniversary of his doctorate was celebrated by his friends and former students in 1854, and a medal was struck for the occasion. In the same year Tiedemann published his last book, a history of tobacco and its use.
1. Original Works. A bibliography of Tiedemann’s works is found in Theodor Bischoff (see below). Works include Zoologie, 3 vols. (Landshut, 1808, 1810, 1814); Anatomie des Fischherzens (Landshut, 1809); Anatomie und Naturgeschichte des Drachen (Nuremberg, 1811); Anatomie der kopflosen Missgeburten (Landshut, 1813); Anatomie und Bildungsgeschichte des Gehirns im Fötus der Menschen, nebst einer vergleichenden Darstellung des Hirnbaues in den Thieren (Nuremberg, 1816). French ed. (Paris, 1823), English ed. (Edinburgh, 1826); Anatomie der Röhrenholothurie, des pomeranzen-farbenen Seesterns und Seeigels (Landshut, 1816); Anatomie und Naturgeschichte des Krokodils (Heidelberg, 1817), with M. Oppel and J. Liboschitz. Other works include Abhandlung über das vermeintliche bärenartige Faulthier (Heidelberg, 1820); Versuche über die Wege auf welchen die Substanzen aus dem Magen und Darm ins Blut gelangen, über die Verrichtung der Milz und über die geheimen Harnwege (Heidelberg, 1820), French ed. (Paris, 1821), with Gmelin; Icones cerebri simiarum et quorundam mammalium variorum (Heidelberg, 1821); Tabulae arteriarum corporis humani (Karlsruhe, 1822); Tabulae nervorum uteri (Heidelberg, 1823); Die Verdauung nach Versuchen (Heidelberg, 1826, 1827), with Gmelin; Physiologie des Menschen: I, Allgemeine Betrachtungen der organischen Körper (Darmstadt, 1830); II, not published; III. Untersuchungen über das Nahrungsbedürfniss, der Nahrungstrieb und die Nahrungsmittel der Menschen (Darmstadt, 1836); On the Brain of the Negro Compared With That of the European and the Orang-Outang (London, 1836), German ed. (Heidelberg, 1837); Von den Duverneyschen, Bartolinschen oder Cowperschen Drüsen des Weibes und der schiefen Gestaltung und Lage der Gebärmutter (Heidelberg, 1840); Von der Verengerung und Verschliessung der Pulsadern in Krankheiten (Heidelberg, 1843); Von lebenden Würmern und Insekten in den Geruchs-Organen des Menschen, den Zufällen, welche sie verursachen und den Mitteln sie auszutreiben (Mannheim, 1844); Zeitschrift für Physiologie, ed. with G. R. and L. Ch. Treviranus; and Geschichte des Tabaks und anderer ähnlichen Genussmittel (Frankfurt am Main, 1854).
II. Secondary Literature. An important study of Tiedemann’s life and works is Theodor Bischoff, Gedächtnissrede auf Friedrich Tiedemann (Munich, 1861), with bibliography, pp. 36–39. Other biographical studies are P. Flourens, “Tiedemann, Friedrich,” in Biographie universelle ancienne et moderne, XLI,526–529, and in Gazette médicale de Paris, 29 , no. 52 (1861); J. Pagel, in Allegemeine Deutsche Biographie, XXXVIII (1894), 577–578; F. Seitz, in Biographisches Lexikon hervorragender Aerzte aller Zeiten und Völker, V (1934), 586–587; E. Stübler, in Geschichte der Medizinischen Fakultät der Universität Heidelberg, 1386–1925 (Heidelberg, 1926), 248–253.
Discussions of Tiedemann’s work include (in chronological order) N. Mani, “Das Werk von Friedrich Tiedemann und Leopold Gmelin: ’Die Verdauung nach Versuchen; und seine Bedeutung für die Entwicklund der Ernährungslehre in der ersten Hälfte des 19. Jahrhunderts, “in Gesnerus, 13 (1956), 190–214; and H. Hoepke, “Der Streit der Professoren Tiedemann und Henle umden Neubau des Anatomischen Institutes in Heidelberg (1844–1849),” in Heidelberg Jahrbuch 1961.