When the paralysis is at first extensive, there appears to be no definite rule as to the parts which are afterwards to recover their power. If an arm and a leg are both affected, the one limb does not necessarily recover sooner or more completely than the other. The only indication is the persistence of contractility in the palsied muscles. Each muscle should be carefully tested by the faradic current, and in those whose contractility is not destroyed we may hope for eventual recovery. Cases have been re corded—notably by Dr. Kennedy—in which the limbs recovered early and completely without the disease leaving any trace of its passage ; but it has been doubted if in such instances the lesion is the same as in those where recovery is slow and more or less imperfect.
In course of time changes take place in the muscles which remain per manently paralysed after the general restoration of power. This stage of the disease is called the period of atrophy ; for the affected muscles waste, and at the same time the slackening of growth in the bone becomes a notice able feature in the case. This arrest of development in the affected limb has been already referred to. It is a variable phenomenon and is not al ways present. When it occurs, it does not appear to be proportioned to the severity of the disease as to muscular wasting and paralysis ; but may be present in a mild case, and absent, or nearly so, in a severe one. Ac cording to Volkmann, it has been seen in cases of the most transient infan tile paralysis where the muscles quickly recovered their power, and atrophy of special muscles was not noticed. As the growth and development of the unaffected limbs proceed in the normal manner, the difference between the two sides is often very evident.
The wasting of the muscles permanently paralysed sometimes begins early, and, according to Duchenne, may be evident at the end of a month. As a rule the permanent paralysis is not widely diffused. It is not com mon to find a whole limb shrunken and useless, although even this mis fortune may occur. Usually it is a group of muscles, or even a single one, which is thus disabled ; and in practice certain parts more than others are found to undergo the atrophic change. In the leg the common exten sor of the toes, the peronei longus and brevis, the tibialis anticus, and sometimes the gastrocnemius may become atrophied ; in the thigh, parts of the triceps extensor ; of the muscles attached to the upper extremity, the deltoid, the serrates magnus, and some of the muscles of the forearm.
One of the most important and characteristic results of the disease con sists in the paralytic contractions which almost invariably occur when mus cles are permanently disabled, and constitute various kinds of deformity. They are especially common in the feet, and are the principal cause of the different forms of clubfoot which develope in the child after birth. The contractions occur not in the paralysed muscles, as a rule, but in those which still retain their contractile power. They begin early, and tend to increase as time goes on. This contraction of unaffected muscles, or of muscles only partially affected, was attributed formerly to the influence of the so-called " muscular tonus." It was supposed that a constant stimulus proceeded from the spinal cord, and kept all healthy muscles in a state of persistent slight contraction. In the normal condition, it was said, oppo
site muscles neutralise each other ; but if the muscles become paralysed on one side, so that the contracting power on that side is abolished, the limb is drawn to the affected side by the action of the " tonus" in the unaffected muscles. This theory was combated by Werner, who maintained that the contraction could be explained without recourse to the imaginary forms. He asserted that when one set of muscles is paralysed, there is no deform ity until the opposite set of muscles is put into action. The limb is then drawn to that side and cannot be replaced by the paralysed antagonistic muscles. It therefore remains in its new position until replaced, or- until it falls back again by its own weight. Consequently, it must happen that the limb is often and long in one position, for the muscles once contracted remain so because the antagonistic muscles can no longer act. Alter a time they lose the power to relax, and a permanent contraction becomes gradually established.
But even this theory does not account for the whole of the facts, for, as was pointed out by C. Hitter, it is not always the muscles anatomically opposed to the paralysed groups which undergo contraction ; and indeed the deviation sometimes occurs in the direction of the paralysed side. The real cause of the deformities of the foot appears from the researches of Hater, Volkmann, and others, to be only partially the unopposed action of healthy muscles and inability to antagonise their contractions. Far more important agents are the weight of the affected part itself and the greater pressure thrown upon it when in use. For instance, the common est deformity of the foot is the talipes equino-varus ; but this is exactly the position in which the foot will fall when the ankle-joint is not acted upon by its muscles. If a child be made to sit upon the edge of a table, with his legs hanging down, the foot instantly falls into the equino-varus position. In paralysis of the limb, if the child has not walked, this is the form the deformity invariably takes. The foot assumes this position, and the shortened muscles in time become permanently contracted. The ar rest of growth in the bone, which is generally present, promotes the for mation of this deformity, for the affected leg being shorter than the other, the child has to point the toes in order to reach the floor. If the paralysis occur in a child who has already learned to walk, the flat foot (talipes val gus) is the usual form of distortion, and is, according to Volkmann, irre spective of the actual muscles paralysed. When the patient brings his weight to bear through the leg upon the sole placed flat on the ground, the foot, being no longer braced up by the paralysed muscles, curves out wards until checked by the ligaments. By repetition of this action the ligaments stretch, and the bones on the compressed side are interfered with in their growth. The talipes valgus thus formed is less perfect than the same deformity produced by over-exercise and fatigue in a child with unparalysed muscles, for during rest the foot is brought again by gravita tion into the equino-varus position. The shortened muscles are therefore again drawn out, and their contraction is less complete, so that the joint is comparatively loose.