General Source of Lead Salts. - Lead is obtained entirely from the native sulphide called galena, by roasting.

General Reactions. - The chief reactions of lead salts are shown in the following table :-

1 T. P. White, Archivf. exp. Path. U. Pharm. 1880, viii. p. 33.

General Impurities. - Alkaline earths, zinc or copper.

General Tests. - As alkaline earths and zinc are not precipitated by sulphuretted hydrogen, they can be detected by passing this gas through the solution of a lead salt until all the lead has been precipitated as sulphide. On removing the sulphide by filitration, and evaporating the filtrate to dryness, no residue should remain if the lead be pure, U.S.P.

Copper may be detected by precipitating the lead from a solution by sulphuric acid, filtering, and super-saturating with ammonia. If copper be present, the solution will exhibit a blue colour, U.S.P. Insoluble salts, as the oxide, may be dissolved in dilute nitric acid super-saturated with ammonia. The filtrate should show no blue colour.

Action. - Soluble lead-salts unite with albumen, and form albuminate of lead. They have little or no irritating action when applied directly to the denuded skin or to a mucous membrane. In the mouth they have an astringent action, but a sweet instead of a corrosive taste. In large doses in the stomach they may excite vomiting, and may produce symptoms of irritant poisoning. In the intestine they act as powerful astringents. After absorption into the blood lead is carried by the blood to all parts of the body, and there becomes deposited. It appears to be eliminated very slowly, so that when even very minute quantities are taken continuously chronic lead-poisoning may be produced.

One of the most important sources of lead-poisoning of this sort is drinking water. Soft water attacks the leaden pipes in which it may be conveyed, or the cisterns in which it may be stored, and dissolves enough lead to cause lead-poisoning, the small quantity of one grain per gallon appearing to be sufficient.

Hard waters are not injurious, as they cause a coating of phosphate or sulphate of lead to form on the surface of the pipe or cistern, and thus protect it from further attacks. Other sources of lead-poisoning are beer or cider which has stood in the pipes leading to the tap, and snuff, from the decomposition of the lead-foil which surrounds it. There are certain trades the workers in which are very liable to lead-poisoning, such as colour-grinding, painting, plumbing, type-founding and printing (compositors), or persons making stereotype plates. The chief source of poisoning in these trades is the lead which adheres to the hands and is swallowed along with the food, and the precautions to be adopted are cleanliness, washing the hands carefully before taking meals, taking the food in a different room from that in which the work is carried on, changing the clothes when the work is over, and, if necessary, drinking water acidulated with sulphuric acid.

Treatment of chronic lead-poisoning consists in eliminating the poison, first from the tissues and then from the body. Various means have been employed, such as sulphur baths, the internal administration of sulphur, frequent doses of castor oil. As the lead is eliminated by the skin and mucous membrane, sulphur, applied either to the skin or taken internally, will convert it into an insoluble sulphide and prevent its re-absorption. Castor oil will remove from the intestinal canal the lead excreted into it. But the treatment which I employ, and which I find very satisfactory, is to combine the use of iodide of potassium with that of sulphate of magnesium, giving from five to ten grains of the iodide three times a day, and a drachm of the sulphate also three times a day, with an interval of about two hours between the medicines. The object of this treatment is (1) to dissolve the lead deposited in the tissues by means of the iodide (p. 561), and to cause its elimination by the mucus of the alimentary canal, and (2) to render the lead insoluble after it has passed into the intestine by means of the sulphate, and to remove it thence as quickly as possible.

The symptoms of chronic lead-poisoning are a blue line on the gums, lead colic, lead cramps, and lead paralysis. The blue line on the gums may appear when neither the colic, cramps, nor paralysis are present. It appears to be produced by sulphuretted hydrogen in the mouth precipitating the lead as black sulphide in the gums just at the margin of the teeth, and this, shining through the tissue above it, appears of a bluish colour. It is absent when the teeth have been lost, and slight if they are kept clean.

The lead colic may either be preceded by symptoms of digestive derangement, such as loss of appetite, or may appear at once. It is characterised by a tearing pain referred chiefly to the region of the umbilicus, and generally accompanied by obstinate constipation. It is usually, though not always, relieved by pressure, but may sometimes be somewhat increased by it.

Lead cramps are almost entirely confined to the flexor surfaces, specially marked in the calves of the legs, and are usually worse at a change of weather. They may either accompany or succeed the colic.

Lead paralyses are usually confined to the extensor surfaces, and more particularly affect the extensors of the wrist, so that this form of paralysis is sometimes known as wrist-drop. The affected muscles become atrophied, and, as the extensor tendons also act as ligaments of the wrist, the bones of the carpus may become displaced. The paralysis probably depends on an affection of the spinal cord rather than of the muscles themselves; for degeneration of the muscles does not occur until after the paralysis has set in for some time, and the muscles are affected in physiological groups which act together, although supplied by different nerves. Thus the supinator longus, which is rather a flexor than a supinator, escapes in lead-poisoning, while the supinator brevis and extensor muscles in the forearm are paralysed. In peripheral paralysis of the musculo-spinal nerve from cold or pressure the supinator longus is paralysed as well as the others.1

Cerebral symptoms, consisting of headache, delirium, epileptiform convulsions, or stupor and coma, have been described as occurring in lead poisoning, and have been termed encephalo-pathia saturnina. These have been ascribed to cerebritis caused by the action of lead upon the brain, but it seems not impossible that they are really due to uraemia. If this be so they may be regarded as the direct consequences of the action of lead which, by causing the degeneration of the kidneys to be presently described, leads to imperfect elimination of tissue-waste.

Affections of the eye are sometimes associated with the cerebral symptoms just mentioned, and are noticed in cases where there is no kidney disease. Sudden onset of amblyopia without organic changes may occur, but is then usually transient. The amblyopia consists in a general dimness of vision, or in a diminution of the field of vision of one or both eyes. Optic neuritis (papillitis) also occurs in some cases, and may proceed to atrophy.

Chronic lead-poisoning has a tendency to induce cirrhotic changes in the kidneys with albuminuria, the tubules becoming blocked by plugs of lead-carbonate and atrophy ensuing.

Lead appears to cause contraction of the muscular walls of the arteries, and to raise the arterial tension and to slow the heart. This action has been supposed to depend on a local astringent effect upon muscular fibre itself, but as in cases of chronic poisoning the proportion of. lead in the nervous system is much greater than in muscular fibre, it is more probable that these effects are of nervous origin. The contraction of the intestine which gives rise to the colic is probably due rather to the action of the lead upon the nerves of the intestine than upon its muscular coats.

Lead is eliminated, to a slight extent, in the urine, and probably largely by the mucus of the intestinal canal. It appears to check the elimination of uric acid, and, in London, gout occurs very frequently among patients who work in lead.

Lead-salts may be administered in medicinal doses for a considerable time without bringing on any sign of lead-poisoning; but Garrod has observed, and I can confirm the statement, that the administration of medicinal doses of lead-salts will bring on a fit of gout in persons predisposed to it. Lead-poisoning appears to occur readily in gouty subjects.

Uses. - Lead lotions are sometimes applied externally to sprains and bruises. They are useful in relieving the itching and the discomfort of pruritus, and in lessening the discharge of eczema. As injections they may be applied in otorrhoea, vulvitis in children, gonorrhoea, and leucorrhoea. They are not used in ulceration of the cornea, lest lead should be deposited in the ulcer and leave a permanent opacity (p. 216). Internally, lead is used for its local action on the stomach in pyrosis, and on the intestine in diarrhoea and dysentery, and for its astringent action on the vessels in haematemesis, haemoptysis, and bleeding from the kidneys and uterus. It has also been employed in palpitation from hypertrophied heart, and in aortic aneurism.

1 Duchenne's Works, selected by Poore, New Syd. Soc.