In all the conditions just referred to we are very much at a loss in attempting to explain the relation of the phenomena to change of structure in the nerv ous system. This difficulty is much increased by the fact that, whatever be the form of lesion, and however local and limited in its nature, we have the same general result of paralysis affecting both sides of the body idikP: and therefore, practically, the important considerations in paraplegia are limited to the recognition of acute and chronic disease, and caries or injury of hone. When any doubt is entertained with regard to the reality of partial paraplegia, it may he always solved by observing with due care the mode in which the feet are set down in attempting to walk ; there is an indescribable uncertainty about the gait of a paraplegic which imposture can never successfully imitate.
§ 3. Local Paralysis.—It has been already explained, in speak ing of hemiplegia, that this appellation is, in strictness, confined to cases of paralysis not having a central origin. When its cause is nervous, the affection of the nerve is located somewhere after it has emerged from the cerebrospinal axis. Due regard to the extent and special distribution of the affection, and knowledge of the anatomy of the nervous system, form the groundwork for the diagnosis of local paralysis; it is limited to the organ which some particular nerve supplies. The cranial nerves, issuing singly from the brain, afford the most frequent examples; thus we have amaurosis, ptosis of one eyelid, anaesthesia, or palsy of one side of the face, &c. In all such cases we have to assure ourselves well that no other cranial nerve is similarly affected, because, when more than one is implicated, there is good ground for believing not only that the lesion is within the cranium, but that it probably also involves the brain itself. In the case of the fifth and seventh pairs, where contiguity or admixture of fibres of different kinds exists, the relations of paralysis of sensation and motion are some times such, that we can define the exact portion of the nerve in which the disease is seated. Ambiguity is, to a certain extent, in many instances unavoidable ; because while some very slight dis ease within the cranium may produce local paralysis and nothing more, it is yet equally true that this form of palsy may be the first manifestation of serious disorganization.
Pressure of a tumor on the brachial plexus, or upon the crural nerve, may give rise to symptoms of palsy and anaesthesia more or less complete in the limbs to which they are distributed : a not unfrequent instance of this condition is the numbness of the legs during pregnancy.
Some forms of local paralysis are more directly connected with the muscular structure than with the nerve by which it is supplied. This condition is met with—especially affecting the extensors of the forearm—in lead palsy, but also involving to a less degree the flexors. The colic which usually precedes the affection of the forearm, is probably caused by corresponding paralysis of the muscular coat of the intestines.
Drop-wrist is also occasionally met with in over-worked, half starved tailors and needlewomen, without colic, without blue-line, or any evidence of lead poison, and would seem to be produced by the forced and long-continued action of ill-nourished muscles.
Similarly, an over-strain of muscle, on perhaps only one occasion, • is sometimes followed by loss of power. Paralysis of the bladder from distension affords a ready example.
Another cause of local paralysis, which, in the end, becomes general, should be mentioned—viz., fatty degeneration. Its pa thological relations are not understood ; but weakness and wasting of one muscle after another, proceeding in a direction which does not necessarily follow the anatomical relations of the nervous system, may be suspected to be due to this change ; it is not possible to givp any definite rule for its diagnosis.
The history of the case, as has been already remarked, serves to exclude instances in which local paralysis is the la.st remnant of a more general affection, or the only effect of an apoplectic attack; these evidently belong to hemiplegia. In other cases it points out, when the disease has come on suddenly, what has been the exciting cause ; or it indicates, by the slow supervention of the affection, that it is due to some condition of long standing. Such, for example, is the history of colic.
Local paralysis is not generally a disease of grave import: it is much more so when the cranial nerves are the seat of the affection ihan when spinal nerves only are implicated ; and among these considerable differences exist. Facial paralysis, coming on after exposure to cold, is one of the least important. Amaurosis is a very distressing disease to the patient ; but ptosis is a symptom of much more serious consequence in the mind of the physician. Strabismus in childhood, after eclampsia, is common, and not of much consequence; while in the adult its presence is of evil augury, when of recent occurrence. But, as before remarked, the coexistence of affection of two distinct nerves (e. g., facial palsy with strabismus) gives most cause for serious apprehension; or the concurrence of any of them singly with symptoms, however obscure, which can be traced in any way to disease of the brain.
Loss of power is more definite in its indications than loss of sensation, inasmuch as the one is an objective, the other a subjec tive phenomenon ; but yet even loss of power may, to a certain extent, be exaggerated, if not wholly simulated, in incomplete paralysis, by the imaginings of the patient ; and such cases are always more difficult of diagnosis than when the power of motion is entirely lost. Patients often speak of numbness when they do not mean ana3sthesia at all ; there is no loss of feelin 0., but perhaps a sensation of tingling, or formication, to which the name is ap plied. Such cases are rather to be regarded as an indistinct form of neuralgia, than as local paralysis.
The bearing of diagnosis on treatment in all cases of local para lysis, may be summed np in the discovery of its cause, whether that be revealed by the history of the case, or can be gathered from a knowledge of the portion of the nerve which is the seat of lesion, and a consideration of the structures immediately surround ing it, in so far as they may interfere with the transmission of volition and sensation through the nerve fibre.