42 
brum itself,—disease of the dorsal portion of 
the spinal marrow,—induces cerebral paralysis, 
hemiplegia, or paraplegia ; disease compressing 
or destroying the facial nerve, or the cauda 
equina in the lumbar region, induces both 
cerebral and spinal paralysis. In the former 
case we shall i augmented, in the latter 
diminished irritability of the muscular fibre. 
I may now resume the points of this article, 
and observe, 
ist. That the spinal marrow, exclusive of 
the cerebrum, is the source of the muscular 
irritability : 
2d. That the cerebrum is, in its acts of voli- 
tion, an exhauster of that irritability : 
3d. That in muscles separated from their 
nervous cunnexion with the brain we have 
augmented irritability : 
4th. That in muscles separated from their 
nervous connexion with the spinal marrow we 
have, on the contrary, diminished irritability : 
5th. That the degree of the irritability of the 
muscular fibre of paralytic limbs, com 
with that of the muscles of the healthy limbs, 
will afford us a source of diagnosis between 
cerebral and spinal paralysis, and especially 
between 
- Hemiplegia of the face, and 
. Paralysis of the facial nerve ; 
. Hemiplegia of the arm or leg, and 
. Disease of the nerves of these limbs ; * 
. Disease of the spinal marrow in the 
dorsal region, and 
6. Disease of the cauda equina in the 
lumbar region; &c. 
6th. That the greater influence of emotion, 
of certain respiratory acts, of the principle of 
tone, kc. on the muscles of certain paralytic 
limbs than on those of healthy limbs, depends 
on their augmented irritability : 
7th. That the same principle explains the 
greater susceptibility of the muscles in certain 
cases of paralytic limbs, to the influence of 
strychnine : 
8th. That, in the conclusions of M. Fouquier, 
Professor Miiller, &c., a sufficient distinction 
was not made between the influence of the 
cerebrum and of the spinal marrow, which in 
this, as in so many other respects, have such 
different properties : 
9th. From these and other experiments and 
observations, I conclude, too, that sleep restores 
the irritability of the muscular system, by 
arresting the acts of volition which exhaust or 
diminish it; muscular efforts, on the other 
hand, diminish the irritability and induce 
fatigue. 
Before I conclude, I must beg my reader’s 
attention to some experiments of that able phy- 
siologist, Dr. J. Reid, of Edinburgh, which 
appear, at first sight, to be contradictory to 
those which I have just detailed. 
Dr. J. Reid’s paper is published in the 
Or won 
* In disease of the cervical vertebre the arms 
are sometimes paralyzed without paralysis of the 
legs; this probably arises from compression of the 
brachial plexus. See Sir B. Brodie’s paper in the 
Medico-chirurgical Transactions, vol. xx. p. 130; 
the galvanic trough would determine the question. 
IRRITABILITY. 
of the British Associs ‘ion 
Fourth Report 
the Advancement of Science, p. 671. I 
follows :— ry 
* Although prseloyen are still divided 
opinion as to the question whether nerves f 
nish a condition necessary to the irritation 
muscles, (i.e. whether every stimulus 
excites a muscle to contraction acts 0 
through the intervention of nervous filamen 
they have now very generally abandoned 
once prevalent theory, that the irritability 
muscles is derived from the brain or sp 
cord, i. e. that muscles are continually 
ceiving, through their nerves, from — 
larger masses of the nervous system, supp 
of a certain influence or energy, which e 
them to contract; and that some of the 
ments of Dr. Wilson Philip, in particular, ; 
seuerslly regarded as decisive against | 
eory. 
E Dr. Wilson Philip found by experi 
that the irritability of a muscle of which 
nerves were entire, was exhausted by applyi 
a stimulus directly to the muscular fik 
(sprinkling salt on them) even more quick 
than that of a muscle of which the nerves h 
been cut, and where all communication wi 
the yg source of nervous influence | 
energy had been cut off; and he states gem 
rally that a muscle of voluntary motion, if « 
hausted by stimulation, will recover its irri 
lity by rest, although all its nerves have 
divided. ¥ 
** But in opposition to this statement, at 
in support of the old theory of nervous ii 
ence continually flowing through certain of t 
nerves into the muscles, it has lately been state 
by Mr. J. W. Earle, that when nerves | 
the limb of a frog were cut, the skin strip 
off, and the muscles irritated by sprinkling sé 
on their fibres, until they had lost their pows 
of contraction, although they did not lose th 
power much more quickly than when the nervs 
were entire, yet they did not regain their pow 
although left undisturbed for five weeks; wh 
the muscles of the limbs of another frog, sim 
larly treated, but of which the nerves were le 
entire, completely recovered their irritabilit 
* Tt occurred as a fundamental objection 
the experiment of Mr. Earle, that in the ea: 
where the nerves had been divided, the m 
cles had become inflamed ; being found at # 
end of the five weeks ‘ softer in their 
than natural, a good deal injected with b 
and with some interstitial deposition of fluid 
them ;’ while in the limb to which the salt 
been applied, but of which the nerves 
entire, and where the irritability was recovere 
‘ although the colour.of the muscles was rath 
darker than natural, their texture remained u 
changed, and there was no interstitial depos 
tion of fluid in them.’ cntll 
* In these circumstances it might eviden 
be supposed that it was the inflammation an 
disorganization of the muscles, not the sectior 
of the nerves, which prevented the recovery 
the irritability in the case where the nerves hai 
been cut; and it became important to have th 
experiment repeated, with care to avoid suc 
7 
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