The history divides cases of hemiplegia very naturally into those ushered in by a "fit," and those in which there has been no loss of consciousness. In the former class there is no doubt what ever about the character of the paralysis : its cause is manifestly central ; and so far as observations have hitherto gone, its extent throws no light whatever on the particular portion of the brain involved. Sometimes the progress of the case and the duration of the paralysis are of some assistance in determining the nature of the changes which in the first instance caused the fit.
In the latter class the symptoms may have come on gradually or suddenly ; depending, in the one case, on disorganization of the brain, softening, or abscess ; in the other, on extravasation of blood. I am not aware that, in any case, serous effusion has pro duced paralysis without preceding evidence of inflammation, or the occurrence of a fit either distinctly convulsive in character, or more nearly resembling apoplexy. When slowly developed, we seek for evidence of previous disease of the brain in headache, earache, dimness of sight in one eye, double vision, ptosis, deaf ness, or impairment of intellectual power, loss of memory, &c. Occasionally, while such circumstances point to some form of chronic disease of the brain, the paralysis itself comes on rapidly ; in other instances this is the only symptom ; it begins with par tial failure of the power of volition over certain muscles, and gradually increases both in extent and intensity. When depend ent on extravasation of blood, the patient has probably been in his usual state of health up to the period of seizure ; suddenly he becomes conscious of numbness, or loss of power in one of his limbs, and the paralysis soon involves the greater part of that side of the body. Occasionally the occurrence of headache leads to a strong presumption in favor of extravasation ; but this is not the rule in such cases.
The diagnosis between hemiplegia and local paralysis—between loss of power depending on changes occurring within the cranium, and those affecting the nerve or the muscle—in all cases in which the history fails to point out symptoms directly connected with the encephalon, must rest entirely upon the distribution of the affection in its relation to the anatomy of the nervous system. If we find that the palsy includes muscles supplied by nerves which have different origins, and have no direct communication with each other at their exit, we may be certain that the disorder is central.
Hemiplegia is very rarely indeed associated with disease of the spinal cord : the space in the canal is so limited, that pressure on one-half is sure to affect the other, although, perhaps, in slighter degree ; and the two halves are so intimately united,.that inflammation of the one never fails also to attack the other : paralysis of one side of the body is therefore always found with a minor degree of the same affection on the other. when the disease is situated in the cord, and the ease must be considered as one of paraplegia.
In sows cases, hemiplegia may be traced ip a tumor within the cranium.: its presence may be first shown by the occurrence of local paralysis of one of the cranial nerves, produced simply by pressure on its tract ; hence it was said that the cause of local paralysis had no necessary connection with the nerve centres. In such a case the effect of the tumor within the cranium is just the same as it would have been had it pressed on the nerve after it bad emerged from the skull. When it has attained some size, it may destroy a portion of the brain in which several nerves take their origin, causing paralysis of each, and then we have a case of partial hemiplegia—no longer one of local paraly sis : or it may paralyze several nerves by mere pressure, and though in that case it would in reality be an instance of compound local paralysis, yet we should not be wrong in assigning to it an intra-cranial cause, which is all that diagnosis can assert with any degree of confidence. It does not appear that such tumors can by their mere size produce more general hemiplegia : when this occurs, it almost certainly depends on the coincidence of inflammation, which has led to softening of the brain or effusion of serum. The only posit ble exception is when the pressure is exerted on a portion of the medulla ob longata, and then paraplegia is the usual if not the invariable result.
By far the most common cause of hemiplegia is extravasation of blood in the hemisphere of the brain opposite to the side of the body affected ; but why this event causes in one case both apoplexy and paralysis, in another apoplexy alone, and in a third only hemiplegia, we are not always able to determine. It is to be rememberel that while, on the hand, hemiplegia does not necessarily follow on apoplexy, so, on the other, its continuance after consciousness is restored must not be taken as proving that the fit has been of the nature of sanguineous apoplexy ; because it is sometimes dependent on effusion of serum, when one lateral ventricle is more distended than the other. Extravasation of blood in the brain is so often found associated with disease of the heart and arteries, that apart from any consideration of caus ality, the discovery of valvular lesion, or hypertrophy, affords strong presump tive evidence, in cases of hemiplegia, that they belong to this class rather than to serous effusion or chronic disease. In connection with this subject we must again refer to the plugging up of an artery by a mass of fibrin de tached from a diseased valve. In -most cases the paralysis is produced by disorganization of brain resulting from imperfect nutrition ; but it also ap pears to be sometimes the immediate effect of the stoppage of the supply of blood, when the symptoms are necessarily more quickly developed than in the other instance; but neither present the character of rapidity belonging to ex travasation. and in neither is there anything like an apoplectic attack.