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Originally appearing in Volume V20, Page 765 of the 1911 Encyclopedia Britannica.
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PARALLEL MOTION, a form of link-work invented by James Watt, and used in steam-engines (see STEAM-ENGINE, § 88), to connect the head of the piston rod, moving up and down in a vertical path, with the end of the beam, moving in the arc of a circle. An ordinary form is shown diagrammatically in figure. MN is the path in F•=- iG l0 Watt's Parallel Motion. or disease of nervous and muscular structures, and is then termed organic paralysis; or (2) from purely dynamic disturbances in the nervous structures of the brain which preside over voluntary movement. The latter is functional motor paralysis, a symptom common in certain neuroses, especially hysteria. For general paralysis of the insane, see INSANITY. Whether the loss of motor power be functional or organic in origin, it may be generalized in all the muscles of the body, or localized to one or many. The different forms of paralysis of the voluntary muscles which may arise from organic disease can be understood by a consideration of the motor path of voluntary impulses from brain to muscle. There are two neural segments in this path, an upper cerebral and a lower spinal; the former has its departure platform in the brain and its terminus in the whole of the anterior grey matter of the spinal cord, whence issues the lower spinal segment of the motor path to the muscles. The nerve fibres of the upper cerebral segment are prolongations of the large psycho-motor cells; the nerve fibres of the lower segment are prolongations by the anterior roots and motor nerves of the large cells in the grey matter of the cord. Disease or destruction of any part of the upper cerebral segment will give rise to loss of voluntary power, for the influence of the mind on the muscles is removed in proportion to the destruction of this efferent path (see diagram in NEUROPATHOLOGY). Disease or destruction of the lower spinal segment causes not only loss of voluntary power but an atrophy of the muscles themselves. Paralysis may therefore be divided into three great groups: (I) loss of voluntary power without muscular wasting except from disuse, and without electrical changes in the muscles due to injury or disease of the upper cerebral segment of the motor path of volition; (2) loss of muscular power with wasting and electrical changes in the muscles due to disease or injury of the lower spinal segment formed by the cells of the grey matter of the spinal cord, the anterior roots and the peripheral motor nerves; (3) primary wasting of the muscles. The more common forms of paralysis will now be described. r. Hemiplegia, or paralysis affecting one side of the body, is a frequent result of apoplexy (q.v.); there is loss of motion of the tongue, face, trunk and extremities on the side of the body opposite the lesion in the brain. In a case of severe complete hemiplegia both arm and leg are powerless; the face is paralysed chiefly in the lower part, while the upper part moves almost as well as on the unparalysed side, and the eye can be shut at will, unlike peripheral facial paralysis (Bell's palsy). The tongue when protruded deviates towards the paralysed side, and the muscles of mastication contract equally in ordinary action, although difficulty arises in eating, from food accumulating between the cheek and gums on the paralysed side. Speech is thick and indistinct, and when there is right-sided hemiplegia in a right-handed person, there may be associated various forms of aphasia (q.v.), because the speech centres are in the left hemisphere of the brain. Some muscles are completely paralysed, others are merely weakened, while others, e.g. the trunk muscles, are apparently unaffected. In many cases of even complete hemiplegia, improvement, especially in children, takes place after a few weeks or months, and is generally first indicated by return of movement in the muscles which are habitually associated in their action with those of the opposite unparalysed side; thus, movement of the leg returns first at the hip and knee joints, and of the arm at the shoulder and elbow, although the hand may remain motionless. The recovery however in the majority of cases is only partial, and the sufferer of hemiplegia is left with a permanent weakness of one side of the body, often associated with contracture and rigidity, giving rise to a characteristic gait and attitude. The patient in walking leans to the sound side and swings round the affected leg from the hip, the inner side of the toe of the boot scraping the ground as it is raised and advanced. The arm is adducted at the shoulder, flexed at the elbow, wrist and fingers, and resists all attempts at extension. According to the part of the brain damaged variations of paralytic symptoms may arise; thus occasionallythe paralysis may be limited more or less to the face, the arm or the leg. In such case it is termed a monoplegia, a condition sometimes arising from cerebral tumour. Occasionally the face is paralysed on one side and the arm and leg on the other side ; this condition is termed alternate hemiplegia, which is due to the fact that the disease has damaged the motor path from the brain to the leg and arm before it has crossed over to the opposite side, whereas the path to the face muscles is damaged after it has crossed. In rare cases both leg, arm and face on one side may be paralysed—triplegia; or all four limbs—bilateral hemiplegia. Infantile spastic paralysis, infantile diplegia, or as it is sometimes called Little's disease, is a birth palsy caused by injury from protracted labour, the use of forceps or other causes. The symptoms are generally not observed until long after birth. Convulsions are common, and the child is unable to sit up or walk long after the age at which it should do so. Paraplegia is a term applied to paralysis of the lower extremities; there are many causes, but in the great majority of instances it arises from a local or general disease or injury of the spinal cord. A localized transverse myelitis will interrupt the motor and sensory paths which connect the brain with the spinal grey matter below the lesion, and when the destruction is complete, motor and sensory paralysis in all the structures below the injury results; thus fracture, dislocation and disease of the spinal column (e.g. tubercular caries, syphilitic disease of the membranes, localized tumours and haemorrhages) may cause compression and inflammatory softening, and the result is paralysis of the voluntary muscles, loss of sensation, loss of control over the bowel and bladder, and a great tendency to the development cf bed-sores. The muscles do not waste except from disuse, nor undergo electrical changes unless the disease affects extensively the spinal grey matter or roots as well as the cerebral path. When it does so, as in the case of acute spreading myelitis, the symptoms are usually more severe and the outlook is more grave. In cases of focal myelitis from injury or disease, recovery may take place and the return of power and sensation may occur to such an extent that the patient is able to walk long distances; this happy termination in cases of localized disease or injury of the spinal cord often takes place by keeping the patient on his back in bed, daily practising massage and passive movements, and so managing the case as to avoid bedsores and septic inflammation of the bladder—the two dangerous complications which are liable to arise. 2. Paralysis may result from acute inflammatory affections of the spinal cord involving the grey and white matter—myelitis (see NEUROPATHOLOGY). Infantile or Essential Paralysis.—This is a form of spinal paralysis occurring with frequency in young children; in Scandinavian countries the disease is prevalent and sometimes assumes an epidemic form, whereby one is led to believe that it is due to an infective organism. The names infantile and essential paralysis were given before the true nature of the disease in the spinal cord was known; precisely the same affection may occasionally occur, however, in adults, and then it is termed adult spinal paralysis. The medical name for this disease is acute anterior poliomyelitis (Gr. 7ro) uos, grey, and weXbs, marrow), because the anterior grey matter of the spinal cord is the seat of acute inflammation, and destruction of the spinal motor nerve path to the muscles. The extent of the spinal grey matter affected and the degree of destruction of the motor nerve elements which ensues determine the extent and permanency of the paralysis. The term atrophic spinal paralysis is some-times employed as indicating the permanent wasting of muscles that results. Infantile paralysis often commences suddenly, and the paralysis may not be observed until a few days have elapsed ; the earliest symptoms noticeable are fever, convulsions and sometimes vomiting; and, if the child is old enough, it may complain of pains or numbness or tingling in the limb or limbs which are subsequently found to be paralysed. It is characteristic, however, of the disease that there is no loss of sensation 764 in the paralysed limb. The whole of the limb is not necessarily paralysed, often it is only a group of muscles, and even if the paralysis affects both legs or the arm and leg on one side, it generally fails in the uniform distribution of the previously described paraplegia or hemiplegia. The affected muscles rapidly waste and become flaccid, the electrical reactions change, and finally the muscles may cease to respond to electrical stimulation whether of the continuous or interrupted current. In the less severe cases (and they are the most common) only a group of muscles undergo complete paralysis and atrophy, and there is always hope of some return of power in a paralysed limb. Associated with the withered condition of the limb due to the muscular atrophy is an enfeebled circulation, rendering the limb cold, blue and livid; the nutrition of the bones and other parts is involved, so that a limb paralysed in early infancy does not grow and is shorter than its fellow. Deformities arise, some the result of simply failing muscular support; others due to permanent changes in the position of the limbs, for example clubfoot. There is absence of bladder and bowel troubles, and bedsores do not occur; the disease itself is rarely, if ever, fatal. About a month after the onset of the disease local treatment of the atrophied muscles should be commenced, and every effort should be made by massage, by suitable positions and passive movements to promote the circulation and prevent deformities in the affected limbs. Should these measures fail, surgical aid should be sought. Sub-acute and chronic forms of atrophic and spinal paralysis have been described, but some of them were undoubtedly cases of peripheral neuritis. Wasting Palsy. Progressive Muscular Atrophy.—This is a chronic disease characterized by slow and insidious weakness and wasting of groups of muscles due to disease of the anterior spinal grey matter. It begins mostly in adult life between 25 and 45 years of age, and affects males more than females. In the majority of cases it commences in the upper extremities, and the small muscles of the hand are especially liable to be affected. The palmar eminences of the thumb and little finger, owing to the wasting of the muscles, gradually disappear, and a flat ape-like hand is the result; in extreme cases all the small muscles of the hand are atrophied, and a claw-like hand is the result. The muscles which are next most liable to atrophy are those of the shoulder and upper arm, and the atrophy may thence spread to the muscles of the neck and trunk, and the intercostals and even the diaphragm may be affected, causing serious difficulties of respiration. The lower extremities are less often and later affected by wasting. This disease generally runs a slow and progressive course; it may however be years before it spreads from the hand to the arm, and a period of arrest may occur before other muscles become involved. A characteristic feature of the disease is fibrillary twitching of the wasting muscles. The electrical excitability of the muscles is diminished rather than changed, except where the wasting is very extreme, when a partial reaction of degeneration may be obtained. Sensation is unaffected, as the disease is limited to the motor cells of the anterior grey matter (see NEUROPATHOLOGY). There is no affection of the bowel or bladder. Death usually occurs from intercurrent diseases, e.g. bronchitis, pneumonia, or broncho-pneumonia. Some patients die owing to failure of the respiratory muscles; others from the disease spreading to the medulla oblongata (the bulb of the brain) and causing bulbar paralysis. The chronic morbid process leading to decay and destruction of the spinal motor cells which is the essential pathological feature of this disease is generally accompanied, and sometimes preceded, by degeneration of the path of voluntary impulses from the brain. It is then called amyotrophic 'lateral sclerosis, a rapid form of progressive muscular atrophy. Bulbar Paralysis.—A number of different morbid conditions may give rise to a group of symptoms, the principal features of which are paralysis of the muscles concerned in speech, swallowing, phonation and mastication. These symptoms may arise suddenly from vascular lesions or inflammatory processes, which involve the nuclei of origin of the cranial nerves supplyingthe muscles of the tongue, lips, pharynx and larynx.. But there is also a slow degenerative insidious progressive bulbar paralysis affecting both sexes pretty equally; it came on between 40 to 6o years of age, and the cause is unknown. Slight indistinctness of speech, especially in the utterance of consonants requiring the elevation of the tip of the tongue to the dental arch and palate, is usually the first symptom. Later the explosive lip sounds are indistinctly uttered; simultaneously, owing to paralysis of the soft palate, the speech becomes nasal in character and sooner or later, associated with this difficulty of speech, there is a difficulty of swallowing, partly because the tongue is unable to convey the food to the back of the mouth, and it accumulates between the cheeks and gums. Moreover the pharyngeal muscles are unable to seize the food and start the process of swallowing on account of the paralysis of the soft palate; liquids are apt to regurgitate through the nostrils, the patient must therefore be nourished with soft semi-solid food. As the disease proceeds, the difficulty of speech and swallowing is increased by the affection of the laryngeal muscles; the pitch of the voice is lowered and the glottis is imperfectly closed during deglutition; there is consequently a tendency for liquids and food to pass into the larynx and set up fits of coughing, which, however, are ineffectual. Later the muscles of mastication are affected and the disease may extend to the respiratory centre, giving rise to attacks of dyspnoea. The intellectual faculties are as a rule unimpaired, although the facial expression and the curious emotional mobility of the countenance, with a tendency of the patient to burst into tears or laughter, would suggest weak-mindedness. Whilst the lower half of the face is strikingly affected, the upper half retains its normal expression and power of movement. This disease is usually rapidly fatal, since it affects the vital centres, and liability to bronchopneumonia excited by the entrance of food into the air passages is also a constant danger in the later stages. Bulbar Paralysis without Anatomical Change.—This condition is also termed " myasthenia gravis "; it differs from acute and chronic bulbar disease by the absence of muscular atrophy, by normal electrical excitability of the muscles, by a marked development of the paralysis by fatigue, and by considerable remissions of the symptoms. The bulbar symptoms are the most prominent, but all voluntary muscles are more or less affected, especially the eye-muscles. It is a rare disease affecting both sexes equally at almost any age, the causes and pathology of which are unknown. 3. Paralysis resulting from disease or injury of the motor path to the muscles in the peripheral nervous system. Neuritis.—Paralysis may arise in a muscle, a group of muscles, a whole limb, the lower extremities, or there may be a generalized paralysis of voluntary muscles as a result of neuritis. A typical example of neuritis giving rise to paralysis owing to inflammatory swelling and compression is afforded by the facial nerve; this purely motor nerve as it passes out of the skull through a narrow bony passage is easily compressed and its function interfered with, causing a paralysis of the whole of one side of the face and Bell's Palsy. Exposure to a cold draught in a person with rheumatic diathesis is a frequent cause. As an example of simple mechanical compression producing paralysis, crutch Palsy may be cited; it is the result of continuous compression of the musculo-spiral nerve as it winds round the bone of the upper arm. Lead poisoning may give rise to a localized neuritis affecting the posterior inter-osseous nerve, especially in painters and in those whose occupations necessitate excessive use of the extensors of the forearm; the result is wrist drop or lead palsy. Sciatica is a painful inflammatory condition of the sciatic nerve, in which there may be weakness of the muscles; but inability to move the limb is more on account of the pain it causes than on account of paralysis of the muscles. Exposure to cold and wet, e.g. sitting on a damp seat, may lead to sciatica in a gouty or rheumatic person. Multiple neuritis is a painful generalized inflammation of the peripheral nervous system and arises in many toxic conditions of the blood; among the most important are lead, arsenic and chronic alcohol poisoning. It also occurs in diabetes, diphtheria, beri-beri and other conditions (see NEUROPATHOLOGY). A short description of the commonest form will be given. It occurs in chronic alcoholism and especially in women, and is most frequently due to a combination of a septic absorption from some internal disease and the abuse of alcohol. In a marked case the patient may suffer from paraplegia, but it is distinguished from the paraplegia of spinal disease by the fact that there is loss of control of the sphincters only when there is associated dementia, and that instead of the limbs being insensible they are extremely painful on deep pressure. There is wasting of the muscles, and electrical changes in them; frequently there is anaesthesia and analgesia of the skin, which takes a stocking-like distribution. In severe cases the upper limbs may be affected, and all the muscles of the body are more or less liable to be paralysed—even the heart may suffer. The mental condition in such a severe case is usually quite characteristic; there is delirium, the patient is the subject of hallucinations and delusions; there is loss of knowledge of time and place, and illusions of personal identity. A constant symptom is the loss of memory of recent events, while those of early life are easily recollected. Paralyses—termed medically muscular dystrophies—may arise from a primary atrophy of muscle apparently independent of any discoverable change in the nervous system, but due to a congenital developmental defect of the muscles. Heredity plays an important part in the incidence of these diseases, members of the same family being affected with the same type of disease, and at the same period of life. There may be a tendency in a family to the affection of one sex and not the other; on the other hand, children of both sexes may suffer in the same family. It is curious that the majority of cases are males, and that it is transmitted by women who are not themselves its subjects. Many different clinical types have been described based upon the age of onset, the groups of muscles first affected, and the presence or absence of apparent hypertrophy; they are however all varieties of one affection, and in a case where there is an apparent enlargement of muscles there is really atrophy of the contractile muscle fibres and overgrowth of fat and interstitial fibrous tissue; consequently this form of the disease is called pseudo-hyperirophic paralysis. The muscular dystrophies may be divided into two groups according to the period of life in which the malady manifests itself: (r) Those occurring in childhood; (2) those occurring in youth or adult life. In the first group the muscles may be atrophied or apparently hypertrophied. A progressive atrophy of muscles associated with progressive weakness and various disabilities of movement is soon recognized in the relation of cause and effect; but the parents whose first child looks like an infant Hercules, with abnormally large calves and buttocks, cannot for some time appreciate any connexion of this condition with a muscular weakness which is manifested in various ways. The child stands with its feet widely separated; it waddles along rather than walks; it falls easily and rises with difficulty, having to use the hands to push against the floor; it then rests one hand on the knee, and then the other hand on the other knee, and climbs, as it were, up its own thighs in order to assume the erect posture. In this pseudo-hypertrophic form of paralysis the outlook is very grave, and there is little hope of the patient reaching adult life. Paralysis agitans, Shaking Palsy or Parkinson's Disease is a chronic progressive disease of the nervous system occurring late in life, and characterized by weakness,. tremors and stiffness of the muscles associated with a peculiar attitude and gait. The first sign of the disease is weakness followed by tremor of one hand; this consists of continuous movements of the thumb and forefinger as in rolling a pill, or of movements of the hand like beating a tom-tom; then the other hand is affected, and later there is tremor at the ankle. In some cases there is a continual nodding movement of the head. These tremors are at the rate of five per second and cease during sleep. The attitude and gait are very characteristic; the head is bent forward, and the patient in beginning to walk takes slow steps, which soon become short and quick as if he were running after his centre of gravity. The intellect is clear and in marked contrast to the mask-like expression. This disease lasts for years, and but little can be done ih the way of treatment, except passive movements of the limb to prevent contracture. Treatment.—T here are certain general principles in the treatment of all forms of paralysis which may be summarized as follows. 1. Rest in bed and attention to the vital functions of the body, the heart's action, the respiratory functions, nutrition and excretion. The pulse is the best guide to the administration of drugs and stimulants. As regards the respiratory function, one of the dangers of paralysis is an intercurrent pneumonia—sometimes unavoidable, often due, however, to attempts to give nourishment to a patient in an insensible state, with the result that some of the fluid enters the bronchial tubes, when either the reflex protective coughing is not excited or is ineffectual. Attention to the bowels and bladder is most important. A purge at the onset of paralysis is indicated when the pulse is full and of high tension, and the regular action of the bowels is necessary in all conditions. Retention of urine should be carefully avoided, if necessary by the passing of a catheter, but too much emphasis cannot be laid upon the importance of adopting aseptic precautions to avoid infection of the bladder. Daily inspection of the back should be made of all paralysed patients, and precautions taken to keep the skin of all parts exposed to pressure clean; the back should be laved with eau-de-Cologne or spirit to harden the skin. Any sign of a red spot on the back or buttock of the paralysed side should be a warning note of the possibility of a bedsore; zinc powder or ointment should be applied and the effect of pressure on the part be removed if possible by change of posture and by the use of a water-bed. It is important to cover all warm bottles with flannel, for owing to insensibility large blisters, which heal with difficulty, may result. In cases of paraplegia the legs should be covered with warm woollen hand-knitted stockings, and a cradle employed to protect the feet from the continuous weight of the bed-clothes, a fruitful source of foot drop. 2. As soon as the acute symptoms have passed off passive movement and massage may be employed with advantage; in some cases electrical treatment is indicated; but as a rule, especially in children, electrical treatment offers the disadvantage of being painful and not accomplishing more than can be effected by massage and passive movements. When the passive movements are being made the patient should be instructed by the operator to will the movement which he is performing, and thus try to re-establish the connexion of the brain with the muscles through the point of interruption or by a new path if that is not possible. (F. W. Mo.)
PARALLAX (Gr. aapa?X6, alternately)

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