Purkyně (Purkinje), Jan Evangelista
PURKYNě (PURKINJE), JAN EVANGELISTA
(b. Libochovice, Bohemia [now Czechoslovakia], 17 December 1787; d. Prague, Bohemia, 28 July 1869)
physiology, histology, embryology, education.
Purkyně’s name (usually spelled Purkinjie, a form he adopted so as to have pronounced correctly by German speakers) is known today in the eponyms Purkyně cells (in the cerebellum), Purkyně fibers (of the heart), Purkyně (or Purkyně-Sanson) images, Purkyn’s phenomenon (shift in the relative apparent brightness of red and blue in dim light), and Purkyně’s tree (the shadows of the retinal vessels). He was a versatile scholar with wide-ranging interests and an exceptional ability and minute morphological structures. After 1850 Purkyně was concerned mainly with the role that knowledge and science should play in the life of his nation.
Purkyně’s father was manager of an estate of Prince Dietrichustein in northern Bohemia. He stimulated interest in and knowledge of nature in his eldest son, although he died when Jan was only six. The local schoolteacher and parson helped the talented boy, who at the age of ten was admitted as a choirboy to a Piarist monastery on another of the Dietrichstein estates, at Mikulov (Nikolsburg) in southern Moravia, near the Austrian border. Initially handicapped because he knew only Czech, Purkyně soon learned both languages of instruction, German and Latin, and became one of the best students.
When he had completed his secondary education, Purkyně took orders and, after a year of novitiaite, began teaching in a Piarist school at Strážnice, Morevia. In 1806 he was sent to Litomysl in eastern Bohemia to to continue his education at the Piarist Philosophical Institute, the obligatory preparation for “higher” university studies (theology, law, medicine).The writing f contemporary philosophers, however, mainly Fichte’s Über die Bestimmung des Gelerten, led him to abandon an ecclesiastical career (1807) aqnd earn a meager living by tutoring while he completed his philosophical studies in Praque. At that time he attemoted his first research, in physics; an analysis of “acoustic waves,”ingeniously fxed on small vibrating glass plates. Lack of guidance, however; Prevented him from achieving any significant resulted; but he did gain a good grounding in physics that was very valuable for his later work in biology. His most influential teacher was the philosopher and mathematician Bernard Bolzan.
After three years at the estate of Blatná (south of Prague) as tutor to the son of the owner, Baron Hildprandt, Purkyně began to study medicine at Prague, planning a career in science rather than in the practice of medicine. Before completing these studies, Purkyně, inspired by the pedagogical work and ideas of J. H. Pestalozzi and P. E. von Fellenberg, as well as by Novalis’ Lehrlinge zu sais, entertained the idea of founding an institution for education of future scientists.
Purkyně’s main interest, however, was physiology; and a physiological topic—the subjective visual phenomena—was the subject of his inaugural dissertation (1818). He began his academic career as prosector and assistant in anatomy at prague;but his libral, nonconformist thinking and affiliation doomed to failure his attemptsto obtain a permentent appointment. With the help of the Prussian surgrous general, J. N. Rust, and on the recommendation of the influential Berlin professor K. A. Rudolphi, who recognized his ablities, in 1823 he was appointed professor of physiology at Breslau, against the will of the Faculty of medicine. He soon overcame the initial hostility, won the respect and friendship of his colloagues, and became one of the best know teachers at the university. In 1827 he married Rudolphi’s daughter Julia whose death in 1835 left him with two young sons. He did not remarry. In 1850 he returned to Prague, where he remained as professor of pysilogy until his death.
Purkyně’s research—which inculded experimental pharmacology, experimental psycholgy, phonetics, histology, and physical, phonetics, histology, embrology and physical anthropology—falls between the Romanic period, which in central Europe was largly ifluenced by Schelling, and the period of empirical physiology. He considered physiology to be a science based on observation and experiment.
Between 1818 and 1825 Purkyně concentrated on the subjective sensory phenomena, studying them by observation and by experiments on himself because he lacked facilities for other experimental work. He began self-observation of unusual visual sensations as an amusement in his early years but later realized that these phenomena—errors in perception sensations with no adequate external cause, discrepancies between physical cause and evoked sensation—are not change but have a relationship to features in the structure or function of the eye and its nerve connections with with the brain, or to brain, or to some abnormal influence of certain simulations.
Purkyně observed and student the puzzling visual sensations produced by strong intermittent illumination (the “light-shadow figure”) by pressure on the eyeball, or by galvanic stimulation. He also showed the possibility of seeing the shadows fall on the neighboring sensitive elements (for instance, when light is concentrated on a spot of the sclera). In 1855 Heinrich Müller confirmed, through the geometrical relation of the movement of these shadows to that of the light source, that the light-sensitive layer of the retina was not on the inner surface of the eyeball but deeper, at the level of the apexes of the rods and cones.
Much attention has been paid to the “Purkyně phenomennon” or “Purkyně shift” (1825), a change in the apparent relative luminosity of colors in a dimlight (scotopic vision) compared with that in full daylight(photopic vision) that is due—as become known later—to different visual sensory mechanisms (the rods and the cones, respectively). He also discovered the physiological inability of peripheral parts of the retain to distinguish colors, overlooked by all previous specialists. Owing to his exceptional ability to observe himself and to concentrate on the details of sensations, he detected many phenomena that other observers went to great paints to confirm.
In contrast to his contemporaries (mainly Goethe) who made similar observations, Purkyně was aware that the subjective sensory pheenomena were neither exception to the otherwise clear laws of nature nor a matter of change, but that they had a physiological basis, their determinism: “The sensory organs are the finest indicators and analyzers for exploring he pertinent qualities and materials relations making world.” He postulated that to each subjective phenomena, such as the visual errors or illusions the objective truth—that is, the physiological processes in the eye and its connections with the brain. Purkyně could not explain most of these observations, but his description drew attention to them and stimulated further study. Some of them are not yet understood. He also followed these ideas in his studies of other subjective phenomena, mainly the effects of drugs and the phenomena of vertigo.
During the same period Purkyně investigated the possibilities of determining the physical properties of the sensory organs. This was very original, and some of the sensory organs. This was very original, and some of the methods he recommended in 1823—determination of the limits of the visual field (perimetry), examination of the anterior segment of the eye in oblique illumination at the focus of a converging lens and with a microscope (developed later by Gullstrand), the usage of the reflected images, and illumination of the fund us of the eye—were developed later and are used still in routine clinical examinations.
The reflex image arising from the outer surface of the cornea had long been know; but the other three images described by Purkyně are extremely faint and thus not easy to detect, so that their discovery was a brilliant achievement. Images due to reflection from the anterior and posterior surfaces of the crystalline lens were independently rediscovered by Louis Sanson fourteen years later, but that of the posterior surface of the cornea was not confirmed until fifty years later—and then only by use of a special device. Purkyně also realized the importance of these reflex images in ophthalmology, for appraising the transparency of the optic media of eye and for determining the curvature of each reflecting (and refracting) surface. He recommended measuring the sizes of the images by use of a microscope fifted with a micrometer and comparing them with similar images of glass balls of different sizes. Later Helmholtz and others deneloped special instruments for this purpose. The change in the size of the second image, meanured by Langenbeck in 1849, elucidated the nature of the change in the accommodation.
Most important, but overlooked and unrecognized in its time, was Purkyně’s recommendation that the interior of the eye be examined in light reflected into it by a concave lens, a principle later used by Helmholtz in his ophthalmoscope (1851).
His 1823 Breaslau dissertation also contained his renowned classification of the fingerprints.
From 1820 to 1827 Purkyně studied vertigo and the physiological phenomena of the maintenance of posture and equilibrium. He was attracted by the observation of Erasmus Darwin that when one stops, after rotating for a period round the body axis, the apparent motion of the surroundings changes from horizontal to vertical when the head is inclined. He investigated this observation systematically and found that three is also an exact determinism in these subjective motion is determined by the position of the head during the rotation Purkyně’s law of vertigo). The involuntary muscular reactions of the limbs and of the eyes (nystagmus) also depend on the position of the during head the primary rotation. He pointed out that these reaction have a compaensatory charactre, that their purpose is to oppose the apparent motion, and that they follow the law of vertigo. Purkyně also studied “galvanic vertigo,” the sensation of an apparent movement toward the anode that is compensated for by a real deviation in the opposite direction. His experiments on animals, made with his pupil C.H.W Krauss, showed the importance of the cerebellum in these reactions. Purkyně´s observations and experiment complemented those of Flourens; but neither man fully grasped the implications of the other’s result and he phenomena they described remained puzzling for the next fifty years. In 1873–1874 Breuer, Mach and Crun Brown reported almost simultaneously on the role of the vestibular receptors in the maintenance of equilibrium and orientation. In the 1820’s, however, the idea that the inner ear is the organ of hearing was so firmly fixed that no one could conceive that it is also the seat of spcial organs for sensing and transmitting to the brain the position and movements of the head.
In 1825–1832 Purkyně studied the early development of the avian egg in the body of the female. His discovery and isolation of a minute structure, the germinal vesicle (“Purkyně’s vesicle”), on the spot of the yolk where the embryo develops—later identified with the cell nucleus—formed a bridge between the large avian egg and the small ova of other animals. It also stimulated the work of K.E von Baer that led in 1827 to the discovery of the ovum in mammals and man. Purkyeneě’s pupil A. Bernhardt contributed to the final elucidation of Baer’s interpretation in 1835.
In this period Purkyně concluded his studies of vertigo (1827) and of the effects of drug (1829). Noteworthy are his description of visual sensation produced by toxic does of digitails and belladona, and his conception of physiological pharmacology. He then began research on what he called the physiology of the human language (phonetics), again mainly by observations on himself. His work greatly influenced the further studies of J. N. Czermak and E. W. Brücke. His main report, howver, was lost at the Berlin Academy of Sciences and was not published until the 1970’s.
Stimulated by his colleague A. W. Henschel, Purkyně studied plant studientplant structures, mainly the elastic fibrous cells of the anthers and the form of the pollen and spores in relation to the mechanism of their dispersion. In his extensive comparative study, combining anatomy with physiology, he distinguished structural types, and drew attention to mechanical factors and the role of cells in the differentiation of plant tissues. His dynamic concept was recognized mainly by French botanists.
During his first years of teaching, Purkyně thought often of physiology, both as a science and as a medical discipline. He was opposed to the speculative treatment of physiology that prevailed in central Europe at that time. He repeatedly stated that physiology is a science based on observation and experiment and, like physics and chemistry, is experimental science. This conviction entailed practical instruction, which he began in 1824. But as his practical course and his experimental research met with difficulties and obstacles, Purkyně realized the need for an independent department of physiology; and from 1831 he fought for its establishment against indifference, lack of understanding, and hostile egotism.
In 1832 Purkyně acquired a “great, modern” achromatic microscope made by S. Plössl, one of the best instruments at that time. This was the beginning of a new period in his research (1832–1845), a patient and systematic investigation of structure as the material basis of life phenomena. He wrote to Rudolph Wagner in 1841: “With boundless eagerness I investigated within the shortest time all areas of plant and animal histology, and concluded that this new field was inexhaustible. Nearly every day brought new discoveries, and soon I felt the necessity to make others share my enhanced vision, and to take pleasure in their discoveries.”
Purkyně saw in the microscope many structures that had escaped the attention of other observers; but, once described, they seemed so obvious that younger specialists could hardly believe they had remained unnoticed for so long. He also paid great attention to the preparation of tissues for examination under the microscope—fixing, sectioning, staining, and other means of making visible structures that are not seen in fresh, untreated specimens (acetic acid, for instance, makes the cell nuclei visible). Purkyně constructed a compressorium for a finely graded squeezing of tissue specimens. Later, his assistant A. Oschatz constructed the first plate microtome for cutting thin sections. For the study of bone and teeth Purkyně developed a technique of decalcification prior to sectioning, and one of grinding to thin, transparent layers. He also used amber, copal varnishes, and Canada balsam for embedding.
Purkyně’s systematic and detailed studies, in which his students participated, contributed to the knowledge of the microscopic structure of the skin and its glands (sweat glands and their spiral ducts, the “granular” structure of the basal layer of the epidermis), bone (bone cells, canaliculi with concentric lamellar structure of the matrix), teeth (structure of dentin) and their development (an investigation soon pursued by several other biologists), cartilage (cells, “ground substance”) and arteries and veins. His discovery of the gastric glands (described independently by Sprott Boyd)and of the cellular structure of all other glands led Purkyně to study the digestive action of extracts of gastric and intestinal mucosae and of the pancreas, and to discover several new factors in the digestive process.
The eponym “Purkyně cells” for the large, pearshaped bodies in the cerebellum commemorates Purkyně’s investigation of the structure of the nervous system. He was the first to describe cells as ubiquitous formations in the central nervous system of vertebrates and in their ganglia—as structures that play an important role in nervous activity, “… elementary centres of collection, production and distribution of the force within the nervous system.” He showed that nerve fibers are not hollow tubes; the sheath envelops an axis cylinder formed of an aluminous matter. With his pupil D. Rosenthal, Purkyně examined the number of nerve fibers and their distribution according to their diameters in various roots of spinal nerves and in the cerebral nerves of several animal species, in the belief that both the total number and the relative proportion of thin and thick fibers have a functional significance. This was one of the earliest endeavors in quantitative neurobiology, inspired by the idea that “nature acts according to an eternal law even in the sphere of its most delicate microscopic structures.”
Histology was then regarded as a branch of physiology rather than of morphology; and Purkyně hoped that the microscope would aid in the understanding of life phenomena, a hope that began to materialize more than a century later with electron microscopes of much greater resolving power. Investigating living objects, Purkyně and Gabriel Valentine discovered the ciliary motion in higher animals and thoroughly studied its physiology and pharmacology. Purkyně was also interested in the functional structure of such muscular organs as the heart and the uterus (both gravid and non gravid). In the heart he described a special type of fibers (Purkyně fibers, 1839), flat gray threads with transverse markings (and therefore musular) under the lining of the cavity. In sheep they can be seen with the naked eye; some continue into the muscle columns and others form bridges between them. These fibers forming “Purkyně’s network,” were later shown to have the important specific function of conducting the contraction to all parts of the heart.
The chief advance in Purkyně’s time was Schwann’s formulation of the cell theory. Purkyně was Schwann’s immediate and most important predecessor. His finding of nucleated “granules” (cells) in many animal tissues made the analogy between the basic structural elements of plants and animals more evident, and thus speculations of earlier investigators became a well-founded and sound scientific theory that had a great impact on biological work and thought.
In 1839 Purkyně opened a modest independent physiological institute in Breslau, the first of its kind. The legal act of establishing such an institute with statutes and an appropriation was a break-through highly appreciated by such younger contemporaries as Rudolph Wagner, Rudolf Heidenhain, and Email du Bois-Reymond. Purkyně’s perseverance in pursuing his goal and restating his arguments led to his success and drew greater attention to the essential condition for the steady advancement of life sciences. Physiological institutes were very rare until the middle of the nineteenth century, but after that their number grew until they became a regular part of medical schools.
After 1850, as professor at Prague, Purkyně devoted his energy mainly to organizing and expanding science, especially to promoting education among his Czech countrymen. The return to the vernacular in the eighteenth century led to the adoption of German at the central European universities; thus for many nationalities, including the Czechs, knowledge was the privilege of the few who learned German or another more widely spoken language. Purkyně had had to learn German and Latin in secondary school, but he believed that each nation must have easier access to knowledge. In 1853, therefore, he began publishing a Czech scientific review, ̌iva, and sought to secure the conditions for encouraging science and learning in the Czech language. Purkyně struggled with his adamant German colleagues for the acceptance of Czech as a teaching language at the University of: not found Prague and worked out a detailed plan for a national academy. He was interested in facilitating communication, exchange of knowledge and ideas, and freedom of the press; he also recommended unification of writing in the Slav languages by the general acceptance of the Roman alphabet. Purkyně repeatedly stressed the importance of science and knowledge in practical life. His work in the last period of his was of great importance in the Czech national revival and exerted a lasting effect on the subsequent development of science in his country.
I. Original Works. Purkyně’s writings have been collected in Opera omnia, 12 vols. (Prague, 1919–1973); a thirteenth and last vol., containing his autobiographical works, is in preparation. His Opera selecta (Prague, 1848) contains several important works.
The most complete bibliography, which includes translations and multiple editions, is that by V. Kruta, J. E. Purkyně (1787–1869) Physiologist. A Short Account of His Contributions to the Progress of Physiology With a Bibliography of His Works (Prague, 1969). Some of his correspondence has been collected in J. Jedlicka, ed., Jana Ev. Purkyně Korespondence, 2 vols. (Prague, 1920–1925); and in V. Kruta, Beginnings of the Scientific Career of J. E. Purkyně. Letters With His Friends From the Prague Years 1815–1823 (Brno, 1964). Some separate publications are his correspondence with A. Retzius, in Lychnos (1956 and 1959); with K.E. von Baer, ibid. (1971–1972); with Johannes Müller, in Nova acta Leopoldina, 22 (1961), 213–228; and, in connection with the Berlin meeting of German scientists held in 1828, in Sudhoffs Archiv für Geschlichte der Medizin und der Naturwissenschaften, 57 (1973), 152–170.
II. Secondary Literature. The first biography of Purkyně was published during his lifetime: F.J. Nowakowski žicie; i prace naukowa Jana Purkiniego (Warsaw, 1862). An authoritative short biography is by Heidenhain, in Allgemeine deutsche Biographie (1888). More recent are the biography by V. Kruta and M.Teich,Jan Evangelista Purkyně (Prague, 1962), in Czech with English, French, German, Russian, and Spanish trans.; and the enthusiastic account by H.J. John, “Jan Evangelista Purkyně, Czech Scientist and Patriot, 1787–1869,” in Memoirs of the American Philosophical Society, 49 (1949), which should not be considered altogether reliable. See also the biographical and bibliographical work by V. Kruta, listed, above.
Two valuable collections of essays were published to commemorate the 50th anniversary of Purkyně’s birth: Jan Ev. Purkyně 1787–1937. Sbornik stati (Prague, 1937) and In memoriam Joh. E. Prukyne (Prague, 1937). Other symposia are V.Kruta, ed., Jan Evangelista Prukyne 1787–1869 Centenary Symposium (Brno, 1971); Bohumil Nemec and Otakar Matousek, ed., Jan Ev. Purkyně, Badatel narodni buditel (Purkyně Symposium der deutschen Akademie der Naturforscher Leopoldina in Gemeinschaft mit der tschechoslovakischen Akademie,24 no. 151 (1961). See also E. Lesky, Purkyněs Weg. Wissenschaft, Building und Nation (Vienna-Cologne-Graz, 1970).