IRRITABILITY. 



irritability is diminished, and at length becomes 

 extinct, from its source being cut off. 



We may further deduce, from the facts which 

 have been detailed, that the spinal marrow and 

 not the cerebrum is the special source of the 

 power in the nerves of exciting muscular con- 

 traction, and of the irritability of the muscular 

 fibre ; that the cerebrum is, on the contrary, 

 the exhauster, through its acts of volition, of 

 the muscular irritability. 



As a further deduction from the same facts, 

 we may infer the diagnosis between cerebral 

 and spinal paralysis : mere cerebral paralysis is 

 attended by augmented irritability, whereas 

 spinal paralysis is that which is attended by 

 diminished irritability. This fact will prove 

 useful in many obscure cases. 



Having thus cleared up the physiological 

 question, I proceed to the application of the 

 principle to pathology ; and I may here observe 

 that there is a whole series of phenomena which 

 admit of explanation by its aid. 



And, first, the exception to the rule of aug- 

 mented muscular irritability in paralytic limbs, is 

 obviously dependent upon its existing in the 

 cases of paralysis from the severed influence of 

 the spinal marrow, as distinguished from those 

 arising from the severed influence of the cere- 

 brum merely. 



Secondly, we understand at once why the 

 influence of strychnine is first and most seen in 

 cerebral paralysis in the paralytic limbs. 



But there are still some other points which I 

 must bring before the notice of the reader. 



The first of these is the influence of emotion 

 in paralytic limbs. 



The second is the similar influence of certain 

 acts of respiration; as yawning, sneezing, 

 coughing, &c. 



The third, the similar influence of the tonic 

 power. 



It must have occurred to us all to observe 

 the influence of surprise or agitation on the arm 

 and hand, and perhaps on the leg, of a patient 

 long affected by hemiplegia, whilst the limbs 

 of the healthy side remained unaffected. In 

 this case the influence of the emotion is, like 

 that of strychnine in the case formerly discussed, 

 exerted equally upon the limbs of both sides; 

 but it is the muscles of the paralytic limbs 

 which are most irritable, most susceptible of 

 the stimulus ; it is, therefore, these limbs which 

 are most convulsively affected. 



The same phenomenon is not observed in 

 paraplegia, because the influence of the emotion 

 is cut off from the affected limbs. 



Case 1. I was called to a patient a short 

 time ago, affected at that moment with bron- 

 chitis. He was forty-three years of age, and at 

 the age of twenty-four had been seized with 

 hemiplegia. Recovering from the immediate 

 danger of the attack, he remained hemiplegic, 

 scarcely regaining the use of the hand and arm 

 at all, and only partially that of the leg. 



Whenever this patient is excited by meeting 

 an acquaintance, or in any similar way, he has 

 a little strabismus, and the hand and arm are 

 contracted and convulsed in the most extraor- 

 dinary manner : whenever he coughs, the leg 



is thrown involuntarily upwards. The arm is 

 severed, as it were, from volition, but affected 

 by emotion. 



Similar facts have been observed in regard 

 to the influence of certain respiratory acts, but 

 especially those of yawning, sneezing, &c. 



Dr. Abercrombie details the following inte- 

 resting case in a note to the late Mr. Shaw. 



" I think the following case will be interest- 

 ing to you and Mr. Bell. I had some time 

 ago under my care, a man affected with hemi- 

 plegia of the left side ; the palsy complete, with- 

 out the least attempt at motion, except under 

 the following circumstances : he was very much 

 affected with yawning, and every time he 

 yawned the paralytic arm was raised up, with a 

 firm steady motion, until it was at right angles 

 with his body (as he lay in bed on his back), 

 the fore-arm a little bent inwards, so that his 

 hand was above his forehead at its greatest 

 elevation. The arm was raised steadily during 

 the inspiration, and when the expiration began 

 seemed to drop down by its own weight, with 

 considerable force. He continued liable to the 

 affection for a considerable time, and it ceased 

 gradually as he began to recover the natural 

 motion of the limb." That is, as I conclude, 

 as the state of augmented irritability was re- 

 moved by the returning acts of volition. 



Not less interesting are the effects of the 

 tonic power. In cases of hemiplegia of long 

 duration, the paralytic limbs, but especially the 

 arms and hands, are drawn into a state of 

 chronic, rigid, contraction. This phenomenon 

 is owing to the principle of tone constantly 

 acting upon muscles now possessing augmented 

 irritability, whilst they are never, or rarely, 

 relaxed by acts of volition. 



A similar effect is seen in idiots born with 

 atrophied cerebrum : the influence of volition 

 is wanting ; that of the spinal marrow, the 

 source, at once, of the tone and of the irrita- 

 bility of the muscular system, is in constant 

 action, and induces chronic contraction, an 

 effect which must, however, be distinguished 

 from that of spasm, which is excited imme- 

 diately by some disease of the spinal marrow 

 itself. 



I may now resume the subject of the action 

 of strychnine on paralytic limbs. It is obvious 

 that the generalization of M. Fouquier, M. Se- 

 galas, and others, that the strychnine attacks 

 the paralytic rather than the healthy limbs, was 

 too hasty. This is only true in those cases of 

 paralysis in which the muscles still remain in 

 nervous connexion with the spinal marrow ; the 

 opposite result is observed in those other cases 

 in which such connection between the muscles 

 and the spinal marrow is intercepted. 



I would here make another observation. The 

 arms and hands, generally speaking, are more 

 under the influence of the cerebrum than the 

 lower extremities; and these, on the other 

 hand, are more under the influence of the 

 spinal marrow than the arms and hands. The 

 superior extremities are more and more fre- 

 quently affected by hemiplegia than the inferior; 

 these are more influenced by tetanus, by 

 strychnine, &c. than the former, a fact which 



