(b. Ghent, Belgium, 24 August 1851; d. Liège, Belgium, 2 September 1935)
After his secondary studies in Ghent, Fredericq entered the University of Ghent in October 1868. His vocation was clearly defined: he intended to study natural sciences. After obtaining his doctor’s degree in 1871 he became Préparateur for the physiology course at the Faculty of Medicine and at the same time followed the medical curriculum. After receiving his M.D. in 1875, Fredericq went to Paris, where he attended the lectures of Ranvier and G. Pouchet, and to Strasbourg, where he attended the lectures of Waldeyer, E. Tiegel, A. Kundt, and especially Hoppe-Seyler, professor of biochemistry, who allowed him to spend the afternoons in his laboratory to learn biochemical techniques. In the summer of 1876 he went to the marine biological laboratory at Roscoff, where, under Lacaze-Duthiers, he studied the nervous physiology of sea urchins.
Back in Ghent in October 1876, Fredericq began his classic work on blood coagulation. In December he moved to the laboratory of Paul Bert in Paris, where he learned the techniques of blood-gas analysis. There he completed his first classic experiments comparing the distribution of carbon dioxide between blood cells and blood plasma. These experiments were continued in Ghent, to which he returned in March 1877. During the summer of the same year he went again to Hoppe-Seyler’s laboratory in Strasbourg and began a study of digestion in invertebrates, which he continued in Ghent during that autumn and winter. In April 1878, in order to obtain the degree of docteur spécial in physiology, he presented an important paper on his work on blood coagulation and on blood gases. In this paper Fredericq defined the coagulable protein of the plasma, fibrinogen, after its isolation by heat coagulation at 56°C. In horse plasma he distinguished three protein entities: fibrinogen, paralbumin (now called serum globulin), and serum albumin. He showed that in the lungs, the exchanges of oxygen and carbon dioxide are controlled by simple diffusion. Regarding the transport of carbon dioxide from the tissues to the lungs, Fredericq compared the distribution of the gas between plasma and cells at different partial pressures of carbon dioxide, thus beginning the series of investigations leading to our present knowledge of the transport of carbon dioxide.
During the summer of 1878 Fredericq was again in Roscoff and within a short period completed a masterly study of the physiology of the octopus, in which he described and named the copper-containing oxygen carrier hemocyanin. In December 1878 he worked in Marcy’s laboratory in Paris on respiratory innervation. He subsequently returned to Ghent, where he and G. Vandevelde began a study on the speed of nerve impulse in lobster nerves which was completed at Roscoff during the summer of 1879.
In October 1879 Fredericq was appointed professor of physiology at the University of Liège, succeeding Theodor Schwann, originator of the cell theory. In order to prepare plans for a new physiological institute, Fredericq visited Emil du Bois-Reymond in Berlin, where he came under the lasting influence of the great physiologist. In the first days of 1880 Fredericq settled in Liège; there, in September 1881, he married Bertha Spring, a sister of the chemist Walthère Spring.
In 1882, while at the North Sea, Fredericq tasted the blood of a lobster and of other marine invertebrates and found it as salty as seawater. He then tasted the blood of a number of saltwater fishes but found them not as salty as seawater, or about as salty as the blood of freshwater fishes, which are in turn more salty than fresh water itself. Moreover, while cutting the legs off crabs in order to obtain the blood, Fredericq discovered the phenomenon he called autotomy, the reflex casting off of a part of the body when an animal is attacked, the mechanism of which he explained later. In his blood-tasting experiments, Fredericq discovered the equal salinity of the internal and external media of marine invertebrates, while the blood salinity of bony fishes was found to be independent of their external medium.
During the following years Fredericq continued experiments on osmoregulation and in 1901, at the marine station in Naples, he used cryoscopy to determine the lowering of the freezing point of the bloods and of the juices extracted from the tissues of several animals. He also determined the amount of ash in the two series of samples and accounted for the difference in molecular concentration resulting from the cryoscopy experiments and the weighing of the ash by postulating the existence of important amounts of small organic molecules in the tissues of marine invertebrates and in the blood and tissues of Elasmobranchs. Urea was identified later by E. Rodier (1900) in elasmobranchs, but the intracellular organic components of the marine invertebrates, which compensate for the lack of a high concentration of inorganic constituents in their blood, despite the fact that they must maintain osmotic equilibrium with seawater, were identified only recently as amino acids (M. C. Camien, H. Sarlet, G. Duchâteau, and M. Florkin, 1951).
In March 1882, Fredericq began a series of experiments on the regulation of temperature in mammals. For these studies, he devised a respiratory apparatus which allowed the estimation of the oxygen used by a simple volume determination, without a gas analysis. This apparatus was the ancestor of all devices used for the indirect measurement of metabolism in man. With the help of this apparatus Fredericq showed, among other things, that the curves of heat production and of oxygen consumption both show a minimum, the point of thermic neutrality. He also showed that homoiotherms resist an increase or a decrease in temperature by different mechanisms. The memorable experiments of Legallois, carried out in 1812, had led to the conclusion that the respiratory center must be located in the medulla oblongata. Several physiologists had been reluctant to accept this conclusion. By progressive cooling, Fredericq recorded a number of facts which strengthened the notion that the respiratory center is located in the medulla. This localization was also supported by his cross-circulation experiments, carried out from 1887, in which the blood from the carotid artery of one dog, A, goes to the head of another dog, B, and the head of the latter receives blood only from the first dog. If dog A inspires air poor in oxygen, it is dog B who shows the symptoms of dyspnea. The method of cross circulation has since been used in a great deal of important experimental research.
Research pursued in Pflüger’s laboratory had been interpreted as showing that oxygen and carbon dioxide move from a higher-pressure region to a lowerpressure one, in accordance with the laws of diffusion. On the other hand, in 1888 and 1891, Christian Bohr had published a series of results which tended to show that the lung plays a secretory role in the absorption of oxygen and the elimination of carbon dioxide, both moving in a direction contrary to that which would agree with the laws of diffusion. Fredericq built an aerotonometer more exact than those of his predecessors and, in 1895, showed clearly that gas exchanges obey the laws of diffusion in the gills of aquatic animals as well as in the lungs of air-breathing animals.
The first topic studied by Fredericq in the field of circulation physiology concerned the oscillations of blood pressure. He defined three categories of these oscillations: small, numerous ones corresponding to cardiac beats; less frequent oscillations related to the respiratory movement (Traube–Hering curves); and vasomotor oscillations (Sigmund Mayer’s curves.)
Fredericq is one of the physiologists who has made the greatest contributions to the interpretation of the mechanisms of heart contraction. He recognized that a pulsation starts in the right auricle and spreads rapidly to both auricles, then travels slowly to the bundle of His to radiate through the muscle of both ventricles (1906). Fredericq also studied the phenomenon of fibrillation, described by Ludwig and M. Hoffa in 1850. He demonstrated that ventricular fibrillation has no effect on the auricles and does not cross the bundle of His, while auricular fibrillation, through irregular stimulations through the bundle of His, is the cause of ventricular arrhythmia.
Fredericq’s work remains typical of the classical period of physiology. Centered on such topics as heat regulation, respiration, the heart, and circulation, it has played an important role in laying the bases of experimental medicine.
Fredericq was a man of many talents. An excellent draftsman and watercolorist, a great traveler, a botanist, and an entomologist, he devoted a large part of his activities after retirement to an extensive study of the subalpine region of the Hautes Fagnes in the Ardennes. There he established a scientific station, and a museum of the fauna, flora, and geology of the region bears his name.
Albert I, king of the Belgians, recognized Fredericq’s outstanding merits by making him a baron in 1931.
A complete list of Fredericq’s publications is in his biography by Marcel Florkin, cited below (1943).
On Fredericq and his work, see M. Florkin, Léon Fredericq et les débuts de la physiologie en Belgique (Brussels, 1943); “Emil du Bois-Reymond et Léon Fredericq,” in Chronique de l’Université de Liége (Liège, 1967), pp. 181–198; and “Léon Fredericq, 1851–1935,” in Florilège des sciences en Belgique (Brussels, 1967), pp. 1015–1034; M. Florkin and Z. M. Bacq, Un pionnier de la physiologie. Léon Fredericq (Liège, 1953), a collection of extracts from Fredericq’s works; and P. Nolf, “Léon Fredericq,” in Annuaire de l’Académie royale de Belgique (1937), pp. 47–100.