Lead is one of the most powerful and useful of metallic drugs.

1. Plumbi Oxidum

Plumbi Oxidum. Oxide of Lead. Litharge. PbO.

Characters. - Heavy scales of a pale brick-red colour. Soluble in diluted nitric and acetic acids.

Impurities. - Copper, iron, and carbonates; detected by ordinary tests.

Preparations.

Emplastrum Plumbi. - Lead Plaster. 1 in 2 1/2 of Olive Oil and 1 of Water.

Plumbi Oxidum or its Emplastrum is also contained in Emplastra Ferri, Galbani, Hydrargyri, Resime, Cerati Saponis, and Saponis.

From Plumbi Oxidum is made:

Plumbi Acetas. - Acetate of Lead. "Sugar of Lead." Pb(C2H3O2)2.3H1O.

Source. - Made by dissolving Oxide of Lead in Acetic Acid and Water, and crystallising. PbO + 2C2H4O2 = Pb(C2H3O2)2 + H10.

Characters. - White spongy-looking masses of interlaced acicular, crystals, slightly efflorescent, having an acetous odour and a sweet astringent taste. Solubility, 10 in 25 of water.

Incompatibles. - Hard water, mineral acids and salts, vegetable acids, alkalies, lime-water, iodide of potassium, all vegetable astringents, preparations of opium, albuminous liquids.

Impurity. - Carbonate; detected by turbidity of aqueous solution.

Dose. - 1 to 4 gr.

Preparations.

a. Pilula Plumbi cum Opio. - Acetate of Lead, 6; Opium, 1; Confection of Roses, 1. A 4-gr. pill contains 3 gr. of plumbi acetas, and 1/2 gr. of opium.

Dose. - 3 to 5 gr.

b. Suppositoria Plumbi Composita. - Each 15-gr. suppository contains 3 gr. of acetate of lead, and 1 gr. of opium.

c. Unguentum Plumbi Acetatis. - 12 gr. to 1 oz. benzoated lard.

d. Liquor Plumbi Subacetatis. - "Goulard extract." Pb2C4H6O5, dissolved in water.

Source. - Made by boiling acetate of lead and oxide of lead in water.

Characters. - A dense, clear, colourless liquid, with a sweet astringent and alkaline ion.

From Liquor Plumbi Subacetatis arc prepared:

α. Liquor Plumbi Subacetatis Dilutus. - "Goulard Water." Solution of Subacetate of lead, 1; Rectified spirit, 1; Water, 78.

. Unguentum Plumbi Subacetatis Com-positum.-1 in 5 3/4.

2. Plumbi Carbonas

Plumbi Carbonas. Carbonate of Lead. "White Lead." PbCO3.

Characters. - A heavy white powder. Insoluble in water. Impurities. - Lime; sulphate of lead.

Preparation. Unguentum Plumbi Carbonatis. - 1 in 8.

3. Plumbi Nitras

Plumbi Nitras. Nitrate of Lead. Pb(NO3)2. Source. - Made by dissolving lead in boiling nitric acid slightly diluted, and crystallising out.

Characters. - Colourless octahedral nearly opaque crystals.

From Plumbi Nitras is made:

Plumbi Iodidum. - Iodide of Lead. PbI2.

Source. - Made by mixing solutions of Nitrate of Lead and Iodide of Potassium. Pb2(NO3) + 2KI = PbI2 + 2KNO3.

Characters. - A bright yellow powder or crystalline scales.

Preparations.

a. Emplastrum Plumbi Iodidi. - 1 in 9.

b. Unguentum Plumbi Iodidi. - 1 in 8.

Action And Uses. 1. Immediate Local Action And Uses

Externally. - Lead is said not to be absorbed by the unbroken skin; yet the dilute solution of the subacetate (Goulard water) is of unquestionable value in the treatment of contusions and superficial inflammations, such as erysipelas, and is extensively used in these conditions. In the same form, or as the ointment of the subacetate, it relieves itching; a symptom, the cause and pathological nature of which are still obscure. Lead may be absorbed when applied in the form of ointment, probably by decomposition; and the specific effects to be presently described may arise in this way. Lead salts act readily upon wounds, ulcers, and exposed mucous membranes: (1) precipitating the albuminous fluids which cover their surface, or are flowing from them as a discharge; (2) coagulating the protoplasm of the young cells of the superficial layers; and (3) contracting the small arteries and veins of the part, thus diminishing or even arresting the circulation within them, and preventing the escape of the plasma and blood-cells through their walls; whilst (4) the nerves are probably also depressed. These effects are called, as a whole, astringent, antiphlogistic, and sedative. The solutions of the subacetate are much employed as applications to ulcers, as injections for chronic inflammatory discharges from the vagina, urethra, ulcers, ear, etc., and as a collyrium for the conjunctiva; or the carbonate may be dusted upon ulcers, or used as ointment. The strong solution of the subacetate is a powerful irritant, causing pain and reaction, and is rarely used undiluted. The nitrate is stimulant or even caustic, and is applied to syphilitic onychia and chapped nipples. The iodide, in the form of the unguentum, may be rubbed into enlarged joints, glandular Bwellinga and nodes, its absorptive effect being chiefly referable to the iodine.

Internally. - The local action of lead is first appreciated in the mouth as a peculiar "astringent taste," with a sharp sweetness in the case of the acetate. On the mucous membrane of the throat it acts as already described, coagulating the mucus, producing an astringent effect on the cells and vessels of the part, and causing a sensation of dryness. If inflammation be present it is rapidly controlled; and the subacetate, either painted on in the form of the strong solution, or as a gargle formed of the weak solution, is an efficacious remedy for tonsillitis.

The local action of lead on the stomach and intestine corresponds with what has been described: it diminishes the secretions, contracts the vessels, and arrests or retards the peristaltic movements; whilst it is itself converted into an albuminate by the fluids which it encounters. The acetate is accordingly given with or without opium to arrest haematemosis; and it is one of the most certain drugs in the treatment of obstinate diarrhoea, especially if ulceration be present, and haemorrhage threatening, as in typhoid fever (where it may be advantageously combined with opium), and in tuberculosis of the bowels.

2. Action In The Blood

Lead enters the blood as albuminate, but passes very rapidly through it, and cannot be found in it even after large doses. If lead be given for some time, the blood becomes more watery, and the red corpuscles fewer in number.

3. Specific Action

All the tissues take up lead freely from the blood, and retain it obstinately as albuminate, the central nervous system being the important seat of its deposit, whilst it is even more abundant in the kidneys and liver as the channels of its escape, and in the bones from the sluggishness of their metabolism. Thus combined with the active cells of the body, lead after a time sets up a series of phenomena known as "plumbism." These are pathological, not physiological, effects, and may be briefly said to take the form of dyspepsia, constipation, and colic; a full, tense, and infrequent pulse, with increased cardiac action; disturbances of the urinary flow; neuralgic pains; tremors, followed by paralysis of the muscles, chiefly affecting the extensors of the wrist; anaemia and emaciation.

These symptoms and the results obtained by experiments on animals have been variously interpreted. Some authorities refer them to an irritant action of lead on the involuntary muscular fibres of the stomach, bowels, blood-vessels, similar to its astringent local effects, whence muscular contractions, painful spasms, narrowing of the vessels, and finally paralysis, and other phenomena from exhaustion. Other pharmacologists contend that lead acts primarily on the central nervous system and nerves, and secondarily only on the muscles, vessels, etc. Its remarkable effect in raising the blood pressure has been referred to irritation of the splanchnics, and consequent narrowing of the abdominal vessels; that is, to increased peripheral resistance. The increased blood pressure is the cause of the infrequent powerful cardiac action, and to some extent of the urinary disturbances.

4. Specific Uses

The specific action of lead is turned to many important uses. As a powerful haemostatic it is used in bleeding from the stomach and bowel, as we have said, and also from the lungs, opium being advantageously combined with it to ensure mental and bodily rest (Pilula Plumbi cum Opio, or acetate of lead and acetate of morphia with acetic acid). Its use in diarrhoea is also partly referable to its specific action.

5. Remote Local Action And Uses

Load is slowly excreted in the bile, urine, skin, and milk. In the bowel, the portion that has been excreted by the liver is reabsorbed, is again excreted, and finally escapes in the faeces as the black sulphide. In passing through the kidneys, lead diminishes the excretion of uric acid. It is used as a haamo-slatic in renal haemorrhage, in bronchorrhoea, and in profuse sweating.

6. Action' And Uses Of The Different Salts Of Lead

The special action and uses of the different preparations of lead are as follows: The Acetate is the only salt given internally. The solutions of the Subacetate are the only liquid preparations of the metal, and are used externally as lotions, injections, collyria, etc., as well as in the form of the ointment. The Oxide is made into Emplastrum plumbi, the basis of almost all plasters. The Nitrate is used as a local stimulant or eschar-otic, as described; and pharmaceutically to obtain the Iodide. The latter possesses, as already described, absorptive powers by virtue of the iodine, an effect which the lead probably promotes, Plumbi Carbonas is applied, either as the powder or as an ointment, for astringent purposes, to ulcers and inflamed surfaces.