PHYSIOLOGY OF THE NERVOUS SYSTEM. 
the crura cerebri. (Its extent, indeed, is much 
the same as that which has been assigned by 
motor power and action. I say it is probable this 
is 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 trifacial nerves, in regard to the 
psychical 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.” I 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 Deen and Stilling, in which one-half of the 
aie! 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.”! ! 
{ shall here contrast the points made out by 
Prochaska with the statement of Dr. Hall’s “ real 
objects” as quoted a few paragraphs back. 
1. Prochaska forms a large estimate of the im- 
— of the vis nervosa; he attributes to it a 
igh 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 laws of this force as it is 
developed in the pulp of the nerves, Jeaving the 
enquiry into its 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. 
- 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 
frustis.”” 
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 
heryes 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 
sensorium commune. 
10. This reflexion of sensitive impressions into 
motor ones is a physical ph independent of 
the mind. 
ll. The mind, however, may or may not be con- 
scious of its occurrence. 
_ 12. Examples of refiex acts of this kind are found 
in sneezing, in the winking of the eye when the 
finger is suddenly directed A 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 ipretaces 
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 resi- 
T22a 
Prochaska to his sensorium commune.) 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 of 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 (physical ), 
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 fee] 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 thata 
work like this onght 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, Mr. 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, 
