Climate.—In the absence of definite statistics upon the subject, it appears probable that the dangers of chronic lead-poisoning would be greater in warm than in cold climates. The clinical features of the affection are alike in all parts of the globe.
Age.—The majority of individuals attacked are adults. Nevertheless, children employed in occupations involving exposure to lead are attacked with great frequency—so much so that it may be concluded that their liability is in fact greater than that of adults.
Sex exerts a decided influence, women being, under nearly similar circumstances, less frequently attacked than the men employed in the same factories—a fact to be explained only by their greater willingness to exercise the recognized precautions.
Diet does not constitute a predisposing influence. It is nevertheless probable that a deficient diet favors the development of the affection. Excesses in food, and especially excesses in drink, predispose to lead colic.
The mode of life is important. Those who lead sober, regular, and, above all, cleanly lives are less liable to the affection than the intemperate, irregular, and careless. Particularly are the dangers in factories increased by neglect of ventilation. Persons suffering from affections of the digestive tract are not, among lead-workers, more prone to lead colic than their comrades who are free from such diseases.
B. The Exciting Cause.—Metallic lead is probably inert, but, owing to the ease and rapidity with which it oxidizes and forms salts, lead in any form, if introduced into the body continuously for a length of time, produces characteristic toxic effects. The oxides, acetates, and carbonate of lead, being soluble in the gastric juice, act more surely.3 But the sulphate, the least soluble of the lead compounds, may also have this effect (Gasserow).
3 Naunyn, Ziemssen's Encyclopædia, vol. xvii.
The channels by which lead is introduced into the body are the alimentary canal, the respiratory tract, and the cutaneous surface. Hence the modes of introduction are of almost endless variety. The conveyance of lead into the stomach constitutes the most common as well as the most important means of access to the organism. This may be in the form of medicine, as the acetate, the unduly prolonged use of which, even in moderate doses, sometimes produces chronic poisoning. Articles of diet are not infrequently contaminated by lead derived from different sources, of which the most common is the lead glaze of earthenware vessels, which is soluble in acid fluids. According to Naunyn, beer drawn through lead pipes may cause chronic lead-poisoning, which has also been frequently ascribed to the use of shot in cleaning bottles used for wine and malt liquors. Drinking-water is occasionally contaminated with lead derived from pipes made of this metal and cisterns painted with lead colors. Pure water, freed from gases, does not act upon lead when the air is excluded. In the presence of air, however, an oxide of lead is formed which is partially soluble in water. If nitrates, nitrites, and chlorides, such as constitute ingredients of sewage, are also present, they form soluble compounds with lead and increase the proportion of lead salts soluble in the water. For this reason water contaminated by sewage is rendered decidedly more dangerous if carried in leaden pipes. On the other hand, the purer the water the greater the danger. Hence rain-water and pure spring-water cannot safely be stored in cisterns painted with lead colors nor conveyed in leaden pipes, nor can lead covers be used for cisterns, because of the condensation of the vapor of water, which drops back, holding lead salts in solution. The sulphates, phosphates, and carbonates usually found in river-waters form insoluble lead compounds, which, being deposited upon the interior of the pipes, act as protectives and prevent further chemical changes.
Still more common is the accidental conveyance of lead dust and lead compounds to the mouth in consequence of their adhering to the hands or settling from the atmosphere upon articles of food and drink, in the case of workmen engaged in the various arts in which lead is freely used. As a rule, to which the exceptions are rare, the more severe cases of chronic lead-poisoning occur only among workers in lead, as miners, those employed in white-lead factories, painters, typesetters, plumbers, and lapidaries.