By means of these experiments and observa tions we are enabled, I believe, to explain all the apparent discrepancies between the state ments of former authors, and between each of them and my own.
The observations of Nysten and others deter mined that the irritability of the muscular fibre still existed in ordinary hemiplegia ; but they did not extend far enough to determine the comparative degree of irritability of the para lytic and of the healthy limbs, or the question whether, in the former, the irritability was dimi nished—the event probably expected—or aug mented, a result, I believe, never anticipated.
Prochaska and Nysten and Legallois failed in their experiments, too, by not allowing time for the change in the condition of the irritability of the muscular fibre to take place.
Professor Miller and Dr. Sticker, on the other hand, did not distinguish between para lysis arising from separation from the cerebrum merely, and paralysis arising from separation from the spinal marrow, a distinction of the utmost importance in every point of view, and that which explains the phenomenon under discussion. The term paralysis has been used by all the authors whom I have quoted in too general a sense. This is so true that I may affirm that in one kind of paralysis, that which removes the influence of the cerebrum, and which is therefore paralysis of spontaneous or voluntary motion, there is augmented irrita bility; whereas in the other, that which severs the influence of the spinal marrow, the irrita bility is diminished or even annihilated.
We may conclude that in cerebral paralysis the irritability of the muscular fibre becomes augmented from want of the application of the stimulus of volition ; in paralysis arising from disease of the spinal marrow and its nerves this 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.