The principles of physiology by John Augustus Unzer; and A dissertation on the functions of the nervous system, by George Prochaska.

Johann August Unzer

Date:: 1851

Credit: The principles of physiology by John Augustus Unzer; and A dissertation on the functions of the nervous system, by George Prochaska. Source: Wellcome Collection.

Provider: This material has been provided by the Gerstein Science Information Centre at the University of Toronto, through the Medical Heritage Library. The original may be consulted at the Gerstein Science Information Centre, University of Toronto.

66/504 (page 32)

$stimulate a nerve to the performance of its function, although in reality they, act strongly physically; as, for example, a sound which shakes every bone in the head, excites no animal actions in the optic nerves. There is also the mode in which a nerve receives an external impression j for the working of an animal force in the medulla of the nerve is one thing, the propagation to the brain of the impression received by the nerve, another. Then there is nothing in the medulla whereby this transmission can be explained according to mechanical or physical laws. The medulla is neither hard nor elastic, but a soft body, which according to the laws of physics must prevent or arrest the communication of motion. Besides, this transmission takes place so rapidly, and so soon after the external impression is received, that the mind can perceive no space of time to occur between the stimulation of the nerve, and the animal action excited in a part of the body far distant from the point where the impression was made. Nor can this transmission be effected like a motion in fluids, for the medulla is not fluid matter, nor so filled with fluid as to have the mobility of fluids, but is a soft material which retards motion. Lastly, the properties of ethereal fluids are not observable in the medulla, nor even in the vital spirits, as, for example, such as ether, the electric fluid, &c., which transmit motion in an unknown physical way. (Haller^s ' Physiology,' § 379.) Since both the external impression and its transmission along the nerves are operations of the vis nervosa (6), and the aggregate of the animal forces in animal bodies is termed their Senselikeness \_Sinnlichkeit], it follows that the mode in which the medulla of the nerve receives impressions generally, and external impressions particularly (31), as well as the mode in which it transmits them, together indeed with the impression itself, (it being an animal force,) belong to the Sense- likeness [Sinnlichkeit] of animal bodies, and cannot be deduced from or explained by the mechanical and physical laws of motion. 33. There is no difference between the nerves of motion and sensation in respect to the method of receiving and trans- mitting external impressions (14, 31).—See Haller's 'Physiol./ § 384. But as in the present section we have to consider the animal forces abstractedly, and without reference to their motive force on the mechanical machines (16), that which has been stated must be understood to apply to the motor nerves only,$