Further, selection of workers should be made under medical supervision. Workers who suffer from specific disease which, if associated with lead poisoning, may prove dangerous, should be excluded from all contact with lead. Among such illnesses must be reckoned tuberculosis in all its forms, alcoholism, epilepsy, tendency to mental disease (nervous disposition, hysteria, neurasthenia, &c.), rheumatism, and disease of the kidneys. Overtime work undoubtedly increases risk; therefore working hours should be shortened as much as possible, and handwork replaced by machine work where possible. Young persons and women especially should be excluded from work in lead. Alternation of employment also is beneficial and essential in very dangerous lead work, because the poison accumulates in the body and only during intervals wherein absolutely no poison can be absorbed has it time to be eliminated. Periodical medical examination by a surgeon is of great value with systematic entry of the results of examination in a health register. As bearing on this, early diagnosis is of the greatest importance, so that workers in whom the first signs of lead poisoning appear may at once be suspended or transferred to other work. Lead workers should take suitable nourishing food and avoid particularly alcoholic excess. When the danger is due to fumes or dust in the air the measures prescribed on pages 242-55 apply, particularly those which aim at keeping the workrooms and the air in the factories free of them by locally applied exhaust ventilation. In order to replace or reduce the use of lead we strongly advocate the use of non-poisonous, or at any rate less poisonous, substances, where this can be done without technical difficulties, as, for instance, carborundum discs instead of lead in polishing of precious stones, leadless glaze in pottery for lead glaze (so far as this is possible, as to which see page 319), beds free of lead (in different industries) for lead beds. In a number of cases, however, such substitution is impracticable on technical grounds or can only partially be carried out, as, for example, in letterpress printing and in the paint and colour industry, in which the prohibition of lead has often been repeatedly urged. So far, unfortunately, it must be admitted that repeated attempts to find a non-poisonous substitute for lead colours, especially for white lead, of equal value technically, have not succeeded. Endeavours have been made to substitute for lead, zinc preparations (zinc white, lithopone, &c.), but hitherto (in regard to durability, opacity, &c.) with incomplete success.