PHYSIOLOGY OF THE NERVOUS SYSTEM. 



7 22 A 



tlie crura cerebri. (Its extent, indeed, is much 

 the same as that which lias been assigned by 



motor power and action. I say it is probable this 

 i< the case." And in 151 he says, " It has al- 

 ways appeared to me that, observing the difference 

 between the cerebrum and the spinal marrow, the 

 olfactory and the tvifacial nerves, in regard to the 

 ps\chical and the excito- motor properties, it is very 

 improbable that in any part of the nervous system 

 the two functions should co-exist in any one indivi- 

 dual fibre." 1 am, therefore, not premature in 

 refusing to accept as a discovery that which Dr. 

 Hall himself regards only as probable and not 

 proved. Lastly, at 370, he quotes an experiment 

 by Van Been and Stilling, in which one-half of the 

 spinal marrow is divided above the origin of the bra- 

 chial nerves, and the other half below the same point, 

 with the effect of leaving sensation and voluntary 

 motion undestroyed. On this he remarks, "There 

 is, therefore, no continuous rectilinear course of 

 nervous fibre from the brain to the extremities."! ! 



I shall here contrast the points made out by 

 Procha.ska with the statement of Dr Hall's " real 

 objects" as quoted a few paragraphs back. 



1. Prochaska forms a large estimate of the im- 

 portance of the vis nervosa ; he attributes to it a 

 high place among the forces which concur in the 

 production of vital phenomena not limiting the 

 term, as Haller did, to the force by which nerves 

 excite muscles to contract, but viewing it as THE 

 agent in the production of all the phenomena of 

 the nervous system. 



2. He investigates the laivs of this force as it is 

 developed in the pulp of the nerves, leaving the 

 enquiry into iis nature to those who are engaged 

 with physical experiments. 



3. He shows that this nervous force, although 

 in truth an innate property of the medullary pulp, 

 nevertheless needs a stimulus for its developement. 



4. This stimulus, he further shows, may be either 

 physical or mental. 



5. He investigates the causes and effects of the 

 increase and of the diminution of the vis nervosa, 

 and how it is influenced by age, sex, and tem- 

 perament. 



6. He shows that the nervous force remains in 

 nerves separated from the centres (within certain 

 limits) even in " singulis dissectorum nervorum 

 friutis." 



7. Prochaska lays down that nerves act in pro- 

 ducing motion and sensation in virtue of their 

 power of propagating impressions made on them, 

 whether at their origin or at their periphery. 



8. He shows that external impressions made 

 upon sensitive nerves are quickly propagated to 

 their origin and there are reflected, according to a 

 certain law, into corresponding motor nerves, 

 whereby certain definite motions are effected. 



9. This takes place whenever motor and sensitive 

 nerves are implanted in the neighbourhood of each 

 other, and all that part of the cerebro-spinal axis in 

 which nerves are so implanted is called by Prochaska 

 sensoriiiin commune. 



10. This reflexion of sensitive impressions into 

 motor ones is a physical phenomenon, independent of 

 the mind. 



11. The mind, however, may or may not be con- 

 scious of its occurrence. 



12. Examples of reflex acts of this kind are found 

 in sneezing, in the winking of the eye when the 

 finger is suddenly directed close to it, in the violent 

 cough produced by a particle of food or a drop of 

 water passing into the trachea. In all these in- 

 stances the effects of the stimulus applied to the 

 sentient nerves of the part irritated are propagated 

 to the centre, and there reflected into the nerves of 

 those muscles by which the respective movements 

 are produced. 



13. The motions which may be produced in de- 

 capitated animals by excitation of the surface are 

 of this kind, the reflexion taking place in the rcsi- 



Prochaska to his sensorium c<>/i/u/itnc.') These 

 fibres are quite independent of those of sensa- 

 tion and volition and of the sensorium com- 

 mune, using that term as indicating the centre 

 of intellectual actions. Although bound up 

 with sensitive and motor fibres, they are not 

 affected by them, and they maintain their sepa- 

 rate course in the nerves, as well as in the 

 centres.* 



dual portion of the sensorium commune, which is in 

 the spinal marrow ; and those produced in patients 

 labouring under apoplexy are of the same kind. 



14. A similar reflexion takes place in ganglia to 

 that which occurs in the sensorium commune. 



15. Prochaska has, therefore, shown that the 

 nervous centres may affect nerves implanted in them 

 in three ways : 1, through mental change, as in vo- 

 luntary actions ; 2, through a physical change ori- 

 ginating in the centres themselves ; 3, through the 

 reflexion oi the change wrought in a sensitive nerve 

 by peripheral stimulation, into a motor nerve : and 

 that nerves may affect centres, 1, so as to excite a 

 feeling in the mind (sensation) ; and, 2, so as to 

 cause the reflexion of a peripheral change in the 

 afferent sensitive nerve into an adjacent motor 

 nerve, independently of the mind. 



16. Prochaska concludes his observations by 

 drawing a careful distinction between those motions 

 which are animal, being directed by the mind, and 

 those which are mechanical or automatic ( pit y steal ), 

 of which the mind may or may not take cognizance, 

 but in the production of which it takes no part. In 

 these latter are included the reflex actions. 



Such are the conclusions to which Prochaska's 

 observations lead him respecting the nervous system, 

 and in them I confess there appears to me to be a 

 large and an exact view of the phenomena of the 

 nervous system, more comprehensive than the 

 views of Dr. M. Hall respecting an excito-motor 

 power and a special system of excito-motor nerves, 

 and their centre, the true spinal nerves. 



In his latest publication, a volume of essays, 

 (1845) Dr. Hall asserts his conviction of the truth 

 of his views, and re-affirms his claims to discovery. 

 I feel that I owe the reader some apology for this 

 long note. The views of Dr. Hall have been so 

 zealously pressed upon the attention of physiologists 

 and of medical men, that it seemed to me that a 

 work like this ought to contain as full a statement 

 of them as its limits would permit, more especially 

 as I have felt it my duty to express my dissent from 

 them to a very great extent, and to criticize them 

 with much freedom. 



Throughout all my remarks it has been my an- 

 xious wish to express my opinions regarding Dr. 

 Hall's views as of a pure question of science, omit- 

 ting all personal considerations. It would have 

 been infinitely more grateful to my feelings to have 

 been able to express my concurrence in these doc- 

 trines, (as, indeed, I was at one time much dis- 

 posed to do,) than to have found myself compelled 

 by regard to truth to refuse assent to his claims to 

 original discovery as well as to his hypothesis, and 

 even to the accuracy of some of his experiments. 

 The cause of science demands that views which are 

 essentially unsound, but which from the urgency 

 with which they continue to be put forward on va- 

 rious occasions and in various shapes, are in danger 

 of being adopted by those who have no time nor 

 opportunity to investigate them closely, should be 

 exhibited in their real shape and purport by means 

 of a careful and searching analysis. Having 

 weighed them in this balance, I must confess that 

 they have been found wanting. 



* It would be unjust to a most able physiologist 

 and pleasing writer, ?Tr. Grainger, not to state that 

 he has contributed much to the distinct enunciation 

 and apt illustration of this hypothesis. See his 

 excellent work on the Spinal Cord. Lond. 1837. 



