Biographies de neurologues
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mise à jour du
9 janvier 2006
pages 153-155
John Augustus Unzer
Erste Gründe einer Physiologie der eigentlichen thierischen Natur thierischer Körper
Leipzig, Weidmanns Erben und Reich 1771
The principles of physiology
by John Augustus Unzer
and a dissertation on the
Functions of the nervous system
by George Prochaska (1749-1820)
translated et edited by
Thomas Laycock (Göttingen)
The Syndenham Society, London 1851


The Instinct for Repose and Exhilaration. pages 153-155
The animal-sentient forces are exhausted by long activity, and the destruction of the animal would result therefrom if nature had not previously provided against this cause of exhaustion. When the animal-sentient forces (that is to say, the forces of the material ideas, as they may be now considered, in so far as they cause conceptions or sentient actions,) have been uninterruptedly used by the animal for so long a time that any further effort would be injurious, it feels during thought or during the performance of the sentient actions in the body an unpleasant difficulty, which has been termed lassitude, weariness, or fatigue. This unpleasant sensation is the natural stimulus of the instinct for repose or sleep, which instinct consists in an effort to develop the contrary to this unpleasant sensation, that is, the withdrawal of the mind from the wearying thoughts, and letting the animal-sentient forces be inactive, so as to experience the sweetness of repose, and thereby collect new forces, as is the design of the Creator in the instinct and its object with the animal, although the latter knows nothing of the actual intent, namely, the renewal of the strength. Everything which causes the unpleasant sensation of lassitude develops the sensational stimulus for repose, and the instinct itself, the longing for repose. Causes of this kind are hardships, every long-continued movement, meditation, and all longcontinued thought, attention, reflection, and abstraction; also articles of food, or medicines, which interrupt the animal-sentient forces, as wine, opium, heavy meals, pressure in or upon the brain, the plethoric state, various poisons, and numerous others.
The sensational stimulus, namely, the disagreeable external sensation of weariness, manifests its sentient action in the cardiac and respiratory movements, which are at first languid almost to faintness; but in a higher degree the stimulus becomes feverish, and these actions become contra-natural (See also Haller 'Physiology,' ). In so far as the sensational stimulus is a foreseeing of the future sweet repose (the contrary to the disagreeable feeling of lassitude), it manifests its sentient actions in the parts appropriated to the animal-sentient forces, so that it develops imperfectly the future state of repose; and in fact, in the straining of the animal-sentient forces and the effort of the mind to withdraw as much as possible from all external sensations, and spontaneous conceptions, and thereby to interrupt all their sentient actions in the body, consists the sentient actions of the instinct to repose itself, so that the organs which cooperate in the act of thinking, and which produce sentient actions, are compelled involuntarily, by the soul and by a purely corporeal process, to cease their function. Consequently, during the instinct to repose and sleep, the external sensations derived from external impressions, and from the spontaneous conceptions are gradually lost, in consequence of the enfeebling of their material ideas in the brain; the muscles, in so far as they perform sentient actions, move heavily, and let the limbs sink; the eyelids shut, and the whole body totters. In short, the instinct induces imperfectly that condition which comes on when the instinct is satisfied by rest or sleep, and there results from the connection between the physical, mechanical, and animal forces, the repose and renewal of the forces appropriate to sentient actions, in accordance with the object of nature in establishing the instinct (vide Haller's 'Physiology').
Yawning and stretching are rather sentient actions of the instinct for exhilaration, than for rest. For when we feel the unpleasant condition of languor and weariness, we can attain its opposite by new efforts of the animal-sentient forces, as well as by their periodical relaxation during sleep. If, therefore, the obscure stimulus leads us to the former, we then express the anticipated condition of renewed activity of the animal-sentient forces, by imperfect efforts, to which the agreeable obscure foreseeing of the condition of activity excites us. Consequently, although these movements are doubtless signs of weariness, and of the need for sleep, yet they are not sentient actions of the instinct for sleep, but of the instinct for activity, or the waking state. All circumstances that excite the obscure foreseeing of pleasing exhilaration, and, consequently, the above-mentioned causes of weariness render the instinct active, if we desire the antagonistic condition, namely exhilarated activity. Now, as the sight of another person who yawns or stretches himself, reminds us of this condition antagonistic to disagreeable weariness, it leads us to the instinct for exhilaration, and we stretch and yawn with the person.
It still remains to state specially, with reference to the instinct for repose, that the physical and mechanical forces of the machines of animal bodies, as also the vis nervosa on which nerve-actions are dependent, in so far as they are not also at the same time sentient actions, are not subject to this law of nature, namely, that their uninterrupted activity shall cause unpleasant external sensations, and, consequently, induce the stimuli of the instinct for repose and sleep. The formation of the blood, and its continuous internal movement, together with its circulation; the working of the elasticity and other purely physical and mechanical forces of the machines; nay, all those processes of the mechanical machines which during the waking state are sentient actions, but at the same time may be and commonly are, even during the waking state, purely nerveactions, as, for example, the movements of the heart, stomach, intestines, and various muscles, particularly the muscles of respiration, all these, as such, are never accompanied by a sensation of fatigue, never excite the instinct for repose, never stand in need of repose, are never changed by this instinct, nor directly by its satisfaction during the deepest sleep, but go on continuously, and take no further part in it unless they are at the same time sentient actions, or indirectly influenced through the general connection of all the forces of the animal (Haller's 'Physiology'). On these principles, all the phenomena of the animal economy, which depend upon the sensational stimulus to sleep, on the instinct itself, and on the satisfaction of the instinct, or the act of sleeping, may be very readily explained.
A short history of neurology, the bristish contribution.
F. Clifford Rose
Butterworth Heinman Ed, Oxford1999.
Thomas Laycock (1812-1876 and the 'Reflexe cerebral action' p146-147
Thomas Laycock (1812-1876) a physician from York, was 'the first to formulate' reflex action of the brain, in 1844, according to the Dictionary of National Biography . However, in 1851 he translated J.A. Unzer's Principles of Physiology from the German, together with G. Prochaska's Dissertation on the Functions of the Nervous System from the original Latin (Laycock, 1851).
In 1771, Johann August Unzer, 1727-1799, wrote his Erste Gründe einer Physiologie der eigentlichen thierischen Natur thierischer Korper - Principles of a Physiology of the Proper Animal Nature of Animal Bodies. He held that reflex action, as described by Willis, was the functional principle of the nervous system, and that many separate pathways could be followed by careful preparation of brains, something exotic for the sceptic Albrecht von Haller who thought that Unzer was indulging in fantastic dreams. Unzer, in Halle, adhered to the Animist school of Stahl and Juncker which, contrary to the Leibnizian views of Boerhaave and Haller, believed in direct causal interaction of body and soul.
The other one of Laycock's authors, George Prochaska, 1749-1820, was a Vitalist with similar convictions, who also felt a need to account for the many unconscious functions of the brain. This Viennese professor of anatomy and ophthalmology wrote De Usu et Functione Systematis Nervorum (Prochaska, 1800). He concluded that the sensorium commune (the spinal cord, the medulla oblongata and the basal ganglia) reflects the sensorial impressions into motor by definite laws peculiar to itself, and independently of consciousness.
Thus Unzer's and Prochaska's work which Laycock probably knew from the time of his German studies, and of which he knew every single word from his own translation (Laycock, 1851), contained much earlier 'formulations' of reflex action of the brain than Laycock's own work. The reflex theories of both authors can be traced back to Thomas Willis (1621-1675) whose work had been rather neglected in eighteenth century Britain because it was so much more complicated than the simplifications of his contemporary, Sydenham. Laycock's renewal of Unzer's and Prochaska's reflex theories meant that Willis's disparaged ideas returned to Britain after a detour through German lands.
George Prochaska, 1749-1820
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