PARALLELOPIPED 



PARALYSIS 



753 



Parallclopi'ped (Gr. parallelepipedon), a 

 solid figure having six faces, the faces being in- 

 variably parallelograms, and any two opposite 

 faces equal, similar, and parallel. If the faces are 

 all squares, and consequently equal, the parallel- 

 epiped becomes a cube. 



Parallels, in military language, are trenches 

 cut in the ground before a fortress, roughly 

 parallel to its defences, for the purpose of giving 

 cover to the besiegers from the guns of the place. 

 See SIEGE. 



Paralysis. The term paralysis, while ordi- 

 narily used to express loss of power of movement, is 

 used medically in the wider sense of loss of func- 

 tion, so that there may be paralysis of motion, of 

 sensation, of secretion, &c. The term Paresis is 

 used to indicate a diminished activity of function. 

 Thus, paresis of a limb means diminished power of 

 moving the limb. 



From what is said under the articles BRAIN, 

 NERVOUS SYSTEM, and SPINAL CORD it will be 

 seen that paralysis may arise ( 1 ) from destruc- 

 tion of the nerve-cells in the motor area of the 

 surface of the brain; (2) from interruption of 

 the nerve-fibres in their path through the brain 

 to the spinal cord; (3) from interruption of the 

 nerve-fibres in their path through the spinal cord ; 

 (4) from disease of the nerve-cells in the spinal 

 cord; (5) from disease or injury to the nerves 

 passing from the spinal cord to the muscles ; or 

 (6) from affections of the muscles themselves. 

 Thus, we speak of Cerebral, Spinal, and Peripheral 

 Paralyses. 



Cerebral Paralysis. The most common causes 

 of paralysis from brain disease are the rupture 

 of blood-vessels (see APOPLEXY), or the blocking 

 up of the blood-vessels which pass to the surface 

 o{ the brain by clota or other solid particles carried 

 from the heart or larger arteries ( embolism ). Other 

 less frequent causes are tumours, aljscesses, &c. 

 The most usual form of paralysis is that termed 

 Hemiplegia, in which there is paralysis of the 

 leg, arm, and muscles of the mouth and tongue 

 on one side of the Inxly, often accompanied, if the 

 dif;iM> is on the rijjht side, by the condition called 

 Aphasia (q.v.). If the original condition has been 

 such as merely to produce pressure upon the nerves 

 without their actual destruction, it may be com- 

 pletely recovered from. But this is obviously not 

 very frequent. Hemiplegia may be entirely un- 

 accompanied by any paralysis of sensation, but if 

 the fibres which carry sensory impulses to the sur- 

 face of the brain be also destroyed there will be a 

 concomitant loss of sensation on the same side as 

 the loss of motion (hemianajsthesia). In certain 

 case*, when the disease of the brain is in the pons 

 Varolii, the mouth may be paralysed on the oppo- 

 site side from the paralysed limbs. (This depends 

 on anatomical considerations.) Destruction by 

 disease of individual ' motor areas ' will obviously 

 lead to paralysis of the corresponding movements. 



S/i/nril Paralysis is usually the result either ( 1 ) 

 of pressure upon the spinal cord from the results 

 of curvature or injury of the spine, or of growths 

 such as tumours or accesses ; (2) of disease of the 

 spinal cord itself, especially from tumours or acute 

 or chronic inflammations, which may lead to inter- 

 ruption of the nerve-fibres which pass downwards 

 from the brain to the nerve-cells in the gray matter 

 of the spinal cord ; or (3) of direct injury to the 

 spinal cord. If the conducting paths from and to 

 the brain are interrupted in any way, there is com- 

 plete paralysis of voluntary motion and of sensation 

 below the level of the affected part of the spinal 

 cord, l>ecause the motor impulses cannot pass down 

 nor the sensory impulses upwards. At the same 

 time, below the injury reflex movements may be 

 360 



preserved and certain forms even increased. Such 

 spinal paralysis is termed Paraplegia. If the 

 injury to the spinal cord is localised to one side 

 there will be paralysis of the muscles on the same 

 side, supplied by the nerves arising from the cord 

 below the injury, and of sensibility of the opposite 

 side of the boay below the injury (see SPINAL CORD). 



In certain cases the nerve-cells in the anterior 

 horns of the gray matter of the cord (and the 

 same may be said of the corresponding cells of origin 

 of the motor nerves of the brain ) may be diseased 

 without implication of any other part of the spinal 

 cord. The result of this is paralysis of the muscles 

 supplied by those nerve-cells, and consequent gradual 

 wasting of the muscles. Under this head come those 

 frequent localised paralyses in the lower limbs of 

 children (the so-called 'essential paralyses' of 

 children) which affect certain groups of muscles, 

 and lead to such deformities as club-foot and 

 impaired growth of the limbs. A similar disease 

 is sometimes observed in adults (progressive mus- 

 cular atrophy), which runs a very chronic course 

 and leads to a gradual wasting of muscles, the 

 direct result of a corresponding gradual wasting 

 of the nerve-cells in the gray matter of the cord. 

 The disease called 'bulbar paralysis,' in which 

 there is a slow affection of the muscles of the 

 tongue, of the side of the mouth, and of the larynx, 

 is of this nature, its more rapidly fatal termination 

 being due to the implication of structures so neces- 

 sary for organic life. 



Peripheral Paralyses. (a] From Affections of 

 Nerves. These are of extremely frequent occur- 

 rence, and may be due to pressure upon, injury to, 

 or disease of the nerves. The most common of 

 these diseases are the inflammations arising from 

 cold, from the excessive use of alcohol, or from 

 exposure to the poison of lead. If the nerve 

 aSected be a purely motor nerve the resulting 



most commonly either from exposure to draught 

 or from disease of the ear, in the neighbourhood 

 of which the nerve passes through the bones of 

 the skull (see EAR). There results a complete 

 paralysis of the muscles of expression on the cor- 

 responding side of the face ; tlie mouth is twisted 

 to the opposite side, the lips cannot be pursed 

 or retracted, the eye cannot be shut, and the fore- 

 head can be neither raised nor depressed, while 

 the usual furrows on the forehead and cheek 

 are either obliterated or diminished. The disease 

 is in manv cases amenable to treatment, but when 

 associated with disease of the ear it should always 

 be regarded as of grave import. If proper treat- 

 ment be neglected, the paralysed muscles may 

 waste, and recovery become impossible. ' Lead 

 palsy ' is usually indicated by a loss of the power 

 of extending the wrists (wrist-drop) without im- 

 pairment of sensation (see LEAD-POISONING). An 

 example of paralysis resulting from pressure on a 

 nerve is seen in the not uncommon result of sleep- 

 ing with the arms over the bcick of a chair (sleep- 

 ing or crutch palsy ). As the musculo-spinal nerve 

 is compressed, and the muscles which it supplies 

 namely, those which extend the wrist and fingers, 

 and which turn the forearm outwards (supination)-^ 

 are paralysed, there is a wrist-drop like that of lead 

 palsy, but in addition there is loss of sensibility 

 ( anaesthesia ) on the skin of the back of the thumb 

 and first two fingers. 



( b ) From Disease of Muscles. A very remarkable 

 form of paralysis affecting mostly the young is 

 that termed ' psendo-hypertrophic paralysis,' in 

 which the onset of the paralysis, which is 'very 

 gradual, is accompanied by a remarkable apparent 

 overgrowth of the muscles, more especially in the 



