PROCHáSKA, GEORGIUS (JIří)

(b. Blížkovice, Moravia, 10 April 1749; d. Vienna, Austria, 17 July 1820)

anatomy, physiology, embryology, ophthalmology.

Procháska was the son of a smith and smallholder. Two of his older brothers also became smiths, but Procháska, being thought too weak physically to work at the forge, was sent to the Jesuit Gymnasium at Znojmo. When Procháska’s father died in 1763, the family was left with little money to support his further education, but a nearly fatal accident (in which he was poisoned by fumes from a leaking stove in his room) brought Procháska to the attention of the wealthy parents of his schoolmates. He was thereby offered the opportunity to become a private, paid tutor, which enabled him to remain at the Gymnasium. Procháska studied philosophy at Olomouc from 1765 until 1767, then went to Vienna, where he studied medicine from 1770 to 1776. In Vienna he won the patronage of Anton de Haen, to whose clinic he had been taken, critically ill and unable to pay for treatment; de Haen recognized his skill in anatomical drawing, and engaged him as an assistant in his department of clinical teaching.

De Haen died before Procháska had finished his studies, but Procháska found another supporter in Joseph Barth, the cultivated but eccentric professor of anatomy, who gave him an assistantship and taught him his methods of blood-vessel injection and his operation for cataract. In 1778 Procháska was appointed professor of anatomy and ophthalmology at the University of Prague, where from 1786 he also taught “higher anatomy,” physiology, and ophthalmology. In 1791 he returned to Vienna as Barth’s successor as professor of anatomy and ophthalmology. He remained in that post until his retirement in 1819.

Procháska began his own anatomical and physiological research while he was still a student. In 1778 he published his first treatise, on certain questions concerning the strength of the heart and the movement of blood through the blood vessels, entitled Controversae quaestiones …. In this work Procháska demonstrated, through physical models, that the velocity of the blood diminishes as it passes from larger to smaller vessels, in proportion to the increase in the sum of the cross-sectional area of the branches. The treatise provoked a violent reaction from Spallanzani, who was annoyed by the relatively unknown Procháska’s largely justified criticism of his own position. Spallanzans attack on Procháska was published under the pseudonym “A. Castiglioni”; it was shortly answered with a defense signed “Antonius Slawik,” a name that does not appear in any contemporary records or among learned men of the time. Procháska published two other anatomical treatises soon thereafter. These, De carne musculari (1778) and De structura nervorum (1779), were illustrated and contained a number of new observations. In 1780 Procháska’ published a work on the abrasion of human teeth with age, which his pupil J. Pešina later used to work out a system for estimating the age of horses.

Procháska’s 1781 treatise on the generation and origin of monsters set out his views on embryology. He opposed the prevailing notion of preformation, and, based upon his own observations of monsters, argued against the ideas of Bonnet, Haller,Spallanzani, and their supporters. He chose, rather, to champion the view offered by C. F. Wolff, whereby the fetus develops progressively by differentiation from uniform tissues with the emergence of organs and parts that had not existed previously. Procháska went on to point out that such epigenesis offered the best explanation for the development of monsters, an idea that was taken up and elaborated only forty years later.

Procháska’s principal work, Commentatio de functionibus systematis nervosu was published in 1784. In analyzing the function of the nervous system, Procháska was careful to differentiate between facts and theories, endeavoring to explain the workings of the nerves on the basis of observation. He attempted to avoid philosophical considerations and to refute unfounded hypotheses, which he thought to be the main obstacle to a proper understanding of nerve functions. His formulation of reflex action, as an example of nerve activity, is of particular interest. It is based upon the notion of a nerve force (vis nervosa, an analog of Newton’s vis attractiva)and of a sensorium commune, which coordinates all impressions passing to the individual nerve centers. The vis nervosa is divisible and can exist in even severed nerves; a portion of the nervous system can retain its activity although separated from the rest, and it may therefore be seen that the vis nervosa does not proceed from the brain. The neural force is, rather, latent in the nerves, and it remains latent until it is activated by a stimulus. The stimulus may be either internal or external, and the activity of the nerve is dependent upon its intensity. Procháska’s vis nervosa is thus not unlike the modern notion of the nerve impulse.

Procháska postulated the existence of two kinds of nerve fibers. One of these conducts sensory impression from the periphery of the body to the sensorium commune (which extends from the spinal cord through the medulla oblongata and crura cerebri to the thalamus, corresponding approximately to the central gray matter), from which they are reflected as motor impressions. The other conducts “reflected“impulses from the nerve centers to the muscles and other effector organs. Reflection is thus automatic and independent of both the will and the soul; it is not subject to physical laws, and Procháska further rejected any mechanistic explanation. Reflex movements, he believed, could be produced either consciously or unconsciously, without cerebral control, and could even occur in decapitated animals or in anencephalous monsters. He drew a clear distinction between the sensorium commune and the seats of the intellect and the will, and thereby figures in the development of the idea of brain localization. His systematic account and rational synthesis of data were influential on Marshall Hall, F. A. Longet, and Pflüger, among others, largely between 1830 and 1860.

On his return to Vienna, Procháska published several editions of a textbook on physiology as well as some interesting work on the relation of the circulation of the blood to the nutrition of body tissues (such as the growth and simultaneous destruction of bone) and several observations on pathology. From about 1910, he attempted to interpret the phenomena of life according to the romantic tenets of Naturphilosophie.

BIBLIOGRAPHY

I. Original Works. Most of Procháska’s important early works were published or reprinted in two collections: Adnotationum academkaeum, 3 vols. (Prague, 1780–1784); and Operum minonan anatomici, physiologic et pathologici argumenti, 2 vols. (Vienna, 1800). His principal treatise, Commentatio de functionibus systematis nervosi (Prague, 1784), was repr. with a Czech translation, Úvaha o funkcich nervove soustavy (Prague 1954). There is also an English trans, by T. Laycock:A Dissertation on the Functions of the Nervous System (London, 1851). Extracts are in R. J. Herrnstein and E. G. Boring, A Source Book in the History of Psychology (Cambridge, Mass., 1965), 289–299. Later works include Bemerkungen üher den Organismus des menschlichen Körpers und über die denselbenbetreffende arteriösen und venösen Haargefässe nebst den darauf gegründeten Theorie von der Ernährung (Vienna, 1810); and Disquisitio anatomico-physiologica organismi corporis humani eiusque procesus vitalis (Vienna, 1812). His last views are presented in Physiologie oder Lehre über die Natur des Menschen Vienna, 1820).

II. Secondary Literature. A comprehensive biography of Procháska with a bibliography of his writings is V. Kruta, Med. Dr. Jiří Procháska, Zivot, dilo, doba (Prague, 1956). Philosophical aspects of his work were analyzed by J. Ceny; Jiří Procháska a dialektika v némecké přirodni filosofii (Prague, 1960). Short accounts are V. Kruta, “G. Procháska and the Reflex Theory,” in Scripta medica, 34 (1961), 297–314; and Epilepsia, 3 (1962), 446–456; V. Kruta nd Z. Frans, “Un ouvrage de physioligie romantique de G. Procháska,” in Castalia, 22 (1966), 3–12; and M. Neuburger, “Der Physiologe Georg Procháska,” in Wiener medizinische Wochenschrift (1937), 1155–1157. Procháska’s place in the history of neurophysiology is discussed in G. Ganguilhem, la formation du concept de reflexe aux XVII[sup(e)] et XVIII[sup(e)] siècles (Paris, 1955); F.F. Fearing, Reflex Action (Baltimore, 1930); M. Neuburger, Die historische Entwicklung der experimentellen Gehirn-und Rückenmarksphysiologie vor Flourens (Stuttgart, 1897); and J. Soury, Le systeme nerveux central, Structure et fonctions (Paris, 1899).