42 



IRRITABILITY. 



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 observe augmented, in the latter 

 diminished irritability of the muscular fibre. 



I may now resume the points of this article, 

 and observe, 



1st. 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 connexion 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, compared 

 with that of the muscles of the healthy limbs, 

 will afford us a source of diagnosis between 

 cerebral and spinal paralysis, and especially 

 between 



1. Hemiplegia of the face, and 



2. Paralysis of the facial nerve; 



3. Hemiplegia of the arm or leg, and 



4. Disease of the nerves of these limbs ; * 



5. 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, &c. 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 



* In disease of the cervical vertebrae 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 

 Mcdico-chirurgical Transactions, vol. xx. p. 130 j 

 the galvanic trough would determine the question. 



Fourth Report of the British Association for 

 the Advancement of Science, p. 671. It is as 

 follows : 



" Although physiologists are still divided in 

 opinion as to the question whether nerves fur- 

 nish a condition necessary to the irritation of 

 muscles, (i. e. whether every stimulus which 

 excites a muscle to contraction acts on it 

 through the intervention of nervous filaments,) 

 they have now very generally abandoned the 

 once prevalent theory, that the irritability of 

 muscles is derived from the brain or spinal 

 cord, i. e. that muscles are continually re- 

 ceiving, through their nerves, from those 

 larger masses of the nervous system, supplies 

 of a certain influence or energy, which enables 

 them to contract; and that some of the state- 

 ments of Dr. Wilson Philip, in particular, are 

 generally regarded as decisive against this 

 theory. 



" Dr. Wilson Philip found by experiment, 

 that the irritability of a muscle of which the 

 nerves were entire, was exhausted by applying 

 a stimulus directly to the muscular fibres 

 (sprinkling salt on them) even more quickly 

 than that of a muscle of which the nerves had 

 been cut, and where all communication with 

 the supposed source of nervous influence or 

 energy had been cut off; and he states gene- 

 rally that a muscle of voluntary motion, if ex- 

 hausted by stimulation, will recover its irritabi- 

 lity by rest, although all its nerves have been 

 divided. 



" But in opposition to this statement, and 

 in support of the old theory of nervous influ- 

 ence continually flowing through certain of the 

 nerves into the muscles, it has lately been stated 

 by Mr. J. W. Earle, that when the nerves of 

 the limb of a frog were cut, the skin stripped 

 off, and the muscles irritated by sprinkling salt 

 on their fibres, until they had lost their power 

 of contraction, although they did not lose their 

 power much more quickly than when the nerves 

 were entire, yet they did not regain their power, 

 although left undisturbed for five weeks; while 

 the muscles of the limbs of another frog, simi- 

 larly treated, but of which the nerves were left 

 entire, completely recovered their irritability. 



" It occurred as a fundamental objection to 

 the experiment of Mr. Earle, that in the case 

 where the nerves had been divided, the mus- 

 cles had become inflamed ; being found at the 

 end of the five weeks ' softer in their texture 

 than natural, a good deal injected with blood, 

 and with some interstitial deposition of fluid in 

 them ;' while in the limb to which the salt had 

 been applied, but of which the nerves were left 

 entire, and where the irritability was recovered, 

 ' although the colour of the muscles was rather 

 darker than natural, their texture remained un- 

 changed, and there was no interstitial deposi- 

 tion of fluid in them.' 



" In these circumstances it might evidently 

 be supposed that it was the inflammation and 

 disorganization of the muscles, not the section 

 of the nerves, which prevented the recovery of 

 the irritability in the case where the nerves had 

 been cut; and it became important to have the 

 experiment repeated, with care to avoid such 



