LEAD, MEDICAL PROPERTIES OF. In a purely metallic state, lead produces no action on the human system, except such as arises from its mechanical properties ; but as soon as it has become oxidised, it can combine with the contents of the stomach, and produce different effects, according to the nature of the substances it meets with, hence even a leaden bullet, swallowed, has given rise to the symptoms charac teristic of the presence of lead. " In whatever form lead is habitually applied to the body, it is apt to bring on the train of peculiar sym ptoms : the inhalation of its fumes, the habitual contact of any of its compounds with the skin, the prolonged use of them internally as medicines, or externally as ointments and lotions, and the accidental introduction of them for a length of time, with the food, may, sooner or later, equally induce colica pictonum, or painters' colic. Of all expo sures none is more rapid or certain than breathing the vapours or dust of the preparations of lead." (Christison.) Thus the workmen at Lead Hills in Lanarkshire are stated never to have the lead-colic until they work at the smelting furnaces. The action of lead on the human frame differs greatly according to the kind of preparation of lead, the quantity employed, the length of time or frequency of exposure to it, and the channel of its introduction into the body, and idiosyncrasy of the individual. If injected into a vein, acetate of lead, even in small dose, will produce almost immediate effects; while if taken into the stomach it is much slower, and a considerable quantity is requisite to produce serious consequences. In the latter instance the effects are both local and remote : " One class of symptoms indicates inflammation of the alimentary canal; another, spasm of its muscles ; and a third, injury of the nervous system, sometimes apoplexy; more commonly palsy, and that almost always partial and incomplete. Each of these classes of symptoms may exist independently of the other two ; but the last two are more commonly combined." (Christison On Poisons, p. 511.) The rapidity of action is also determined by the solubility of the preparation or salt of lead ; while the degree of effect is also closely connected with the solubility, the more insoluble salts being nearly powerless—a circumstance which supplies a convenient mode of dis arming the others of their virulence by converting them from soluble to insoluble salts. Fatal cases from poisoning by large quantities of the salts of lead are not numerous, as there is in general time to administer antidotes ; but desth from the slow and insidious introduc tido of lead Into the system Is of frequent occurrence. The
principal source of these is the use of water or other fluids con taining lead in solution, the Intermixture of lead, as rubalterationa or accidentally, with articles of food, or handling preparations of lead in the daily holiness of artisans, such as painters, plumbers, fie.
The danger of tieing water from leaden pipes or cisterns was known swim to the Romans, "among whom, however, the reservoirs were either of marble or cement, or of copper lined with tin, or of other metals more precious" (Alderson); nevertheless, pipes and cisterns of lead are still extensively used. and the rarity of any fatal results shows that the risk has been overrated. This is sufficiently explained by the protecting power of the Insoluble salts of lead, formed by the action of the ingredients of the water on the lead, which binders the subsequent surplice of water from coming in contact with the metal. [Leen, C.ol. l44.) No water should ever be drunk or employed for culinary pur pose:a out of sew cisterns ; but water should be allowed to stand in them for some time without being renewed, for only after a crust has been formed does the water become safe; or to expedite this, a little phos phate of rode or Iodide of potassium may be added, or a few drops of sulphuric acid may be used. The expedient of Mr. Chatterton of ap inside lining of gutta pereha to pipes or cisterns removes all danger. The lid or cover of cisterns should never be made of lead, as the vapour which condenses on it pomessee all the solvent power of dis tilled water. It is also unsafe to use water which has flowed over leaden roofs, more particularly in towns, as the surface of the lead is almost invariably coated with some soluble salt ; this Dr. Medlock attributes to nitrous acid being present in the atmosphere of towns. It is, however, an error to attribute all the changes which lead used for roofs or cisterns undergoes solely to the corrosive power of water. (See case by Dr. Wall, quoted in Christison, p. 488, edition 1836.) The holes with which the lead is often riddled are caused by the larva of an insect, the Callidium halftime, in the stomach of which lead is utter' found. ( Kirby and Spence 's Entomolov, p. 235.) The t'rocerna jureneur, Linn. and Anobiunt striatum, likewise perforate lead.