Lead is found native in small masses. It is a dull, whitish metal with a tint of blue, and is not given in its native state, medicinally, but in the form of salts.
The special property of the lead salts is astringency, and they are, in consequence, sedative, anti-phlogistic, and haemostatic.
Used in dilute solutions externally as applications to ulcers, mucous surfaces, etc., they precipitate the albuminous fluids which cover the surface, contract the small blood-vessels, and harden the tissues of the young growing cells. Applied in concentrated solutions, they are irritant, causing inflammation, or increasing it. Taken internally, their action is first evident as a peculiar astringent taste, with a dry feeling of the throat. In the stomach and intestines the same action is shown. Lead dries the secretions, contracts the vessels, and checks peristaltic action, thus causing constipation.
It is changed by the intestinal juices into an albuminate, and so enters the blood. It is rapidly deposited in the tissues, especially in the central nervous system, the kidneys, liver, and bones. It is excreted, but slowly, in the bile, the urine, and perspiration; also by the mammary glands. It diminishes the excretion of uric acid by the kidneys.
Acute lead poisoning is rare, and will be spoken of in connection with the acetate. Chronic poisoning is quite common, the poison being introduced into the system in one or more of the following ways: By absorption through the unbroken skin, as in the case of painters, glaziers, etc. - the fine particles of metal which are rubbed off and adhere to the skin being changed by its secretions into soluble salts which are readily absorbed; by absorption through ulcers, wounds, etc., from the excessive application of ointments; by the use of food put up in cans soldered with lead, cooking utensils made of painted wood or imperfectly burnt pottery, and by eating buns, cake, etc., colored with chromate of lead; by the habit of biting silk thread adulterated with lead; by sleeping or working in newly painted rooms, and by the poisoning of a water supply from lead pipes. This does not occur with "hard" water - viz., that containing salts of lime, as an insoluble coating is then deposited on the lining of the pipes; but with pure, or "soft" water, the lead is slowly dissolved in the form of a carbonate. The first symptoms of poisoning are: A feeling of pain, with a sense of sinking in the region of the navel; loss of appetite, thirst, and dryness of the mouth and throat, with a metallic astringent taste; pale face and skin generally; fetor of the breath; constipation; emaciation and wasting of the muscles, especially those of the arms; swelling of the joints, and rheumatic pains. Colic is a very pronounced symptom, sometimes coming on very suddenly, sometimes after several days' illness. The pain is intense and varies in character, sometimes being sharp, sometimes dull, or, again, "twisting," and seems to centre about the umbilicus. This fact of its being localized differentiates it from hepatic colic, which goes through to the back, and from renal colic, which radiates along the line of the ureters. The abdominal walls are violently retracted and rigid, and neuralgic pains seize the abdominal muscles and shoot along those of the thorax and extremities, especially the flexors. The skin and conjunctivae sometimes become jaundiced, and the urine tinged with bile.
A very striking feature of lead poisoning, occurring both in acute and chronic cases, is the dark slate-coi^red line on the gums along the margin of the incisor teeth. It is said to be more marked in those cases where the tooth-brush is not used.
The chronic nervous symptoms of lead poisoning may be developed after the first attack of colic, or they may come on without marked abdominal disturbance. The most common and noticeable one is the paralysis of the extensor muscles of the forearms, causing what is termed "wrist-drop." With this there is sometimes either partial or complete anaesthesia of the affected members.
Paralysis of the laryngeal muscles sometimes occurs, resulting in aphonia. The pulse is incompressible and tense, full, and infrequent. There may be anaesthesia of the optic nerve as a result of the direct action of lead, or dimness of sight may result from the albuminuria which is often present; and, finally, there may be a condition of cerebral disturbance known as "encephalopathia saturnina," or lead encephalopathy, beginning with headache, and characterized by delirium, stupor, epileptiform convulsions, and coma. Death may follow, although severe cases have been known to recover. Death may also result from the gradual failure of nutrition, or from an extension of paralysis to the muscles of respiration.
In treating chronic lead poisoning, large doses of purgatives are given. Potassium iodide aids in elimination of the poison, and baths of potassium sulphide are also used for this purpose. Workers in lead may guard against poisoning by personal cleanliness, which is of great importance, by the use of sulphuric-acid lemonade, and milk, as a food, in large quantities.