e) Neuritis resulting, from action of poisons introduced from without, such as alcohol, lead, arsenic, mercurials, opium, etc.
(f) The endemic or epidemic form of neuritis, seen in tropical islands and sea coast countries, the well-known 'beri beri" (see BERIBERI, volume i).
(g) The neuritis accompanying cer tain skin eruptions or other trophic changes (HEREEs ZOSTER, see volume iii).
-Whatever the pathological nature or etiological origin of neuritis, if a single nerve or small group of adjacent nerve trunks be affected it is called a "simple neuritis." If a number of nerves in dif ferent portions of the body be simul taneously invaded we have a "multiple neuritis." The neuritis from mechan ical injury, exposure to cold, and other local causes is usually "simple"; the general infections, drug poisonings, and other toxfemias give rise most often to "multiple" neuritis. Of course, there are exceptions to these rules, since a general toxamia may produce only local ized effects—a simple neuritis—and a mechanical injury may involve a large nerve-trunk or several large nerves and give the symptoms of a multiple neu ritis, as has been seen in cases of press ure upon lumbar and sacral nerves of a large aneurism. A simple neuritis is usually "interstitial"; a multiple neu ritis is apt to be chiefly "parenchyma tous." Simple Neuritis.—A simple or local ized neuritis arises from exposure to cold, involving in such cases nerve trunks which lie near the surface of the body the most frequently observed clin ical form being "Bell's paralysis," or "facial paralysis"; from traumatism,— blows or wounds; pressure, as from mor bid growths; aneurisms, sleeping upon arms, crutches used long or injudiciously ("crutch paralysis"); and from lar or other disease which involves the nerves by extension from adjacent af.
fected parts.
In study of neuritis from bicycle riding it was found that if the handle be so constructed as to be grasped at a right angle with the full hand, no injury can result; but if the handle must be grasped at an acute angle, pressure is exerted near the wrist, where the nerves are comparatively superficial, and con siderable damage may be done. Destot (Prov. M6d., June 20, '96).
Neuritis caused by surgical operations is usually due to long-continued pressure (luring ancesthesia, either through force for maintaining the patient in position, by the dragging of the limbs of the table, or by the continued elevation of the arm over the head. To prevent this,
the patient's arms should not be allowed to hang down, and care should be taken that during operation the weight of the body is as evenly distributed as possible. Keeping the body in any constrained position should be avoided when not ab solutely necessary, and the use of any mechanical contrivance for maintaining a desired position should be with due care to prevent nerves from being stretched or pressed upon. H. T. Pershing (Med. New s, Sept. 11, '97).
Number of curious cases of localized neuritis noted following slight injuries, such as too vigorous squeezing of the hands, injury by blow or pressure on the fingers, burning the skin with nitric acid, ete. Occasionally these cases are obstinate, and result in more or less per manent disability. Webber (Boston Med. and Surg. Jour., Nov. 5, '92).
Symptoms.—The symptoms of simple neuritis vary with the cause, nature, and location of the disease, but the true neural symptoms are essentially the same in all, consisting in perversion, ex altation, or, it may be, entire abolition of function of the nerves involved. There is usually pain, of a stabbing, darting character, felt in the parts to which the nerve is distributed, with some pain and tenderness along the course of the nerve. This pain is partly due to pressure or irritation of the nervi nervorum, and may be very intense and distressing or may, as is often the case in mild forms of neuritis, cause little or no inconvenience. There is occasionally cedematous swell ing and redness of the skin over the point of greatest inflammatory activity, and trophic cutaneous affections, sweat ing, and swelling of, and effusions into, joints sometimes appear. Tactile sensa tion is impaired in the affected area, and numbness and formication are frequent. Weakness in the muscles supplied by the affected nerves is the rule, reaching in the severer cases a complete paralysis. Muscular twitchings and spasmodic con tractions are sometimes noted. In the severe and long-continued cases there is apt to be great atrophy of the atTected muscles, which may be followed by con tractures of fingers or toes or other parts involved. The nutrition of the hair and nails is often defective, leading to falling out or grayness of hair, deformities or dropping away of nails, etc.