The mode of action of lead is not yet determined. The view of Henle, that lead acts chiefly upon the unstriped muscular fibre, was at one time generally accepted, and served to explain many of the characteristic phenomena of the disease. On the other hand, there is much in the clinical history to support the opinion of Heubel, that its primary action is upon the nervous system. Whether the peripheral degeneration by which the paralysis is to be explained is primary or secondary to central degeneration in the anterior cornua of the gray matter of the spinal cord, is yet in dispute. Some of the forms of encephalopathy are doubtless due to the nephritis which is found in many cases of chronic lead disease, and are, in fact, symptoms of uræmia. In the great majority of the cases this is not the case. The morbid condition must be explained by the direct toxic action of lead upon the central nervous system. No theory adequate to account for all the cerebral manifestations has yet been suggested. Naunyn has pointed out the resemblance between the nervous and psychical derangements in lead encephalopathy and those which characterize chronic alcoholism, and suggests that lead, like alcohol, produces these effects not as a direct poison, but indirectly in consequence of abnormal nutrition of the whole system, brought about by the continued circulation of a foreign poisonous material in the blood.
Chronic Lead-Poisoning in Animals.—Animals exposed to lead under conditions favorable to the development of the lead affections in man suffer in like manner. Instances of this kind are of frequent occurrence in and about large lead-factories. The drinking of water containing lead also gives rise to these affections in animals. Horses, dogs, cats, and fowls have frequently suffered from lead colic. Horses used in lead-factories suffer from a form of laryngeal obstruction due to lead paralysis of the muscles of the larynx. Relief has followed tracheotomy and the introduction of a canula, and removal to an atmosphere free from lead has resulted in recovery. Cats who spend some time in red-lead workshops frequently are paralyzed. Even the rats in lead-factories become paralytic (Tanquerel).
DIAGNOSIS.—The diagnosis of the affections due to chronic lead-poisoning is, as a rule, unattended with difficulty. The malnutrition, anæmia, poor digestion, foul mouth, stubborn constipation, and the gingival line, considered in connection with the history of prolonged or habitual exposure to lead, would warrant the assumption that the relation between this poison and the symptoms is a causal one. When there is added colic, arthropathies, and paralysis, or the cerebral states having the characters above described, the assumption becomes a certainty. The absence of any one of the ordinary phenomena, such as the blue line or constipation, would still leave the clinical picture sufficiently full to justify the diagnosis. The reaction of degeneration, which is usually marked in saturnine wrist-drop, with the escape of the supinators, distinguishes it from pressure paralysis of the musculo-spiral.
TREATMENT.—A. Prophylaxis.—Free ventilation and scrupulous cleanliness constitute, in general terms, the most efficient safeguards for those whose occupations involve prolonged exposure to lead. Workmen employed in lead-factories and those otherwise exposed to lead should be compelled to wash their hands and change their outer clothing before eating; they should also bathe regularly every day on leaving work; under no circumstances should they be suffered to eat or sleep in or near the workshops. As all kinds of work in the manufacturing of lead preparations are not attended with equal risk, the workers should from time to time be transferred from one department to another or from in-door to out-door work. In order to prevent the constant rising of dust, the floors are to be kept constantly sprinkled or covered with moist sawdust. It is unnecessary to go into further details in regard to the hygiene of the subject. It is probable that towels and sponges worn over the mouth, or other forms of respirators, because of the inconvenience which they occasion and the false sense of security which attends their use, are of less value than has been generally supposed.
It appears scarcely needful to here insist upon the avoidance of cosmetics and hair-dyes containing lead, or upon the exercise of reasonable prudence in the matter of the manufacture, sale, and use of articles of food or drink which are liable either by accident or design to become adulterated with lead compounds.
The use of sulphuric-acid lemonade is a measure of prophylaxis of less real value than was at one time supposed, seeing that the sulphate of lead is in itself capable of producing the disease. Occasional doses of magnesia sulphate are of use where a tendency to constipation exists. Workmen who begins to show signs of chronic lead-poisoning should without delay abandon their work and seek some occupation free from its peculiar dangers.
The precautions against the use of water contaminated with lead have been pointed out under the heading Etiology.
B. Curative Treatment.—When the disease shows itself, no matter in what form, the primary indication is the discontinuance of exposure to lead. Chronic cases of malnutrition, constipation, functional nervous disorder, will occasionally be found upon careful search to depend upon long exposure to lead in some unsuspected way. The cause being removed, such cases often promptly recover.
Measures aimed first at the separation of the lead from the tissues, and then at its elimination from the body, constitute a rational treatment. Sulphur baths and the internal administration of sulphur may be employed with a view of converting the lead eliminated by the skin and mucous membranes into an insoluble sulphide, and thus preventing its resorption. Repeated laxative doses of castor oil will remove unabsorbed lead from the intestinal canal. The plan of treatment at present in general favor consists in the combined use of potassium iodide and magnesium sulphate. From five to twenty grains of the iodide are to be given in not less than six or eight fluidounces of water three times daily, the stomach being empty: two hours after each dose one or two drachms of the magnesium sulphate are to be taken; after this dose an ordinary meal.
This treatment is designed to dissolve the lead deposited in the tissues, and cause its elimination by the mucus of the alimentary canal in part, and to a slight extent also by the urine. The magnesium sulphate tends to remove such lead as finds its way into the alimentary canal thence with all possible rapidity. These measures, together with the removal of the patient from further exposure, exert of themselves a favorable influence upon the malnutrition and anæmia. Quinine, strychnine, iron, cod-liver oil may be advantageously administered as the toxic effects of the lead pass away.