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 (see ). The course of the disease is long, and an attempt should be made to eliminate the lead from the system by purgatives and the administration of potassium iodide.

The diabetic neuritis paraesthesia is slight, and the legs are chiefly affected; weakness and ataxia may be present. Trophic sores on the feet are of frequent occurrence in this variety. The treatment is that of the disease.

Post-diphtheritic neuritis occurs in about 10% of all cases of diphtheria. In this form paralysis of the soft palate is the earliest symptom, and this may be the only one, or the pharynx may be affected. The limbs are affected much later, usually about the 5th or 6th week. Atrophy of the muscles is frequently rapid. If the respiratory muscles are unaffected the prognosis is good, but the paralysis of the limbs may last for several months. The treatment is complete rest, good food and the administration of strychnine.

Acute polyneuritis with numbness and motor weakness has been noted after influenza, together with slight muscular wasting and electrical degeneration. Later, loss of sensation in the peripheral portion of the limbs is complained of, and the motor weakness may affect the muscles of the trunk and face. Such cases tend towards complete recovery.

 NEUROPATHOLOGY, the general name for the science concerned with diseases of the nervous system. As regards the anatomy and physiology, see the articles, , ,, and. The morbid processes affecting the nervous system are numerous and varied, but usually they are clinically divided into two great groups of (1) organic disease, (2) functional disturbance. Such a classification depends upon whether or not symptoms observed during life can be associated with recognizable changes of the nervous system, gross or microscopical, after death. Sometimes this is the morbid process itself, sometimes only the ultimate result of the process. It must be remarked, however, that many diseases which we now look upon as functional may be found due to recognizable changes when suitable methods of investigation shall have been discovered. The paroxysmal neuroses and psychoses may be considered a priori to be due to temporary morbid functional conditions. Our knowledge of the first group is naturally much more advanced than of the latter, for, given certain symptoms during life, we are able, as a rule, to predict not only the nature of the morbid process, but its particular locality.

The histological elements which make up the nervous system may also be divided into two groups: (1) the nervous units or neurones, (2) the supporting, protecting and nutrient tissues. Organic diseases may start primarily in the nervous units or neurones and cause their degeneration; such are true diseases of the nervous system. But the nervous units may be affected secondarily by diseases starting in the supporting, protecting and nutrient tissues of the nervous system; such are essentially diseases within the nervous system, and include diseases of the blood-vessels, lymphatics, membranes and the special nervous connective tissue, neuroglia (a residue of the embryonal structure from which the nervous system was developed). Tumours and new growths must also be included.

The modern conception of the “neurone” as an independent complex cell with branching processes, in physiological rather than anatomical association with other neurones, has modified our ideas of the morbid processes affecting the nervous system, especially as regards degenerations of systems, communities or collections of neurones subserving special functions. It was formerly believed, and generally taught, that the primary systemic degenerations were due to a sclerosis; thus locomotor ataxy was believed to be caused by an overgrowth of the supporting glia tissue of the posterior columns of the spinal cord, which caused a secondary atrophy of the nervous tissue. We now know that this overgrowth of glia tissue is secondary to the atrophy of the nervous elements, and the only true primary overgrowth of glia tissue is really of the nature of the new growth (gliosis). But even in this case it is doubtful if the mere proliferation of the glia tissue elements could destroy the nervous elements, if it were not for the fact that it leads to changes in the vessel walls and to haemorrhages.

The symptoms manifested during life depend upon the nature of the morbid process and the portion of the nervous system affected. A correct understanding of neuropathology involves

the study of (1) the causes which give rise to morbid conditions, which are often complex and due to various combinations of factors arising from without and within the body, and (2) the changes in the structure and functions of the nervous system brought about by intrinsic and extrinsic causes.

The causes of pathological processes occurring in the nervous units (neurones) may be divided into internal and external, and it may be remarked that in all cases except direct injury the two groups are generally more or less combined.

A. Internal Causes.—Of all the causes of nervous disease hereditary predisposition stands pre-eminently first; it may be convergent, paternal, maternal; from grandparents or even more remote ancestors. Moreover, no study of heredity is complete that does not take into consideration collaterals. Especially does this statement apply to functional neuroses, e.g. epilepsy, migraine, hysteria and neurasthenia; and to psychoses, e.g. delusional insanity, mania and melancholia, manic-depressive, recurrent or periodic insanity and dementia-praecox or adolescent insanity.

