The various substances of this group differ markedly in their action. Under this heading come principally chronic metal poisonings, characterised by a general, often very intense, disturbance of nutrition, which justifies their delineation as ‘metabolic poisons’; among these poisons also are included certain others which produce chronic poisoning accompanied by severe disturbance of the peripheral and central nervous system. The corrosive action common to the metal oxides (when acting in a concentrated condition), attributable to the formation of insoluble albuminates, need not, in industrial poisoning, be taken so much into account. The corrosive effect is characteristic only of the compounds, especially of the acid salts of chromium, which, as an acid-forming element, may be classed in the preceding group. Disturbance of health in workmen handling nickel compounds are also ascribed to the corrosive action of these substances. LEAD, LEAD COMPOUNDS Lead poisoning is the most frequent and important chronic industrial poisoning; the symptoms are very varied and associated with the most different groups of organs. We shall describe the typical course of a case of industrial lead poisoning, laying stress, however, on the fact that numerous cases follow an irregular course, in that special symptoms or complications of symptoms are in some especially accentuated, while in others they become less marked or are absent altogether. A premonitory indication of chronic lead poisoning is a blue line on the gum, indicated by a slate gray or bluish black edging to the teeth, the appearance of which is usually accompanied by an unpleasant sweetish taste in the mouth. The cause of this blue line was for some time disputed. It is obviously due to the formation and deposit of sulphide of lead through the action of sulphuretted hydrogen arising from decomposition in the mouth cavity. At the same time a general feeling of malaise and weakness often comes on, occasionally accompanied by tremor of the muscles and disinclination for food, at which stage the sufferer consults the doctor. Frequently he complains also of pains in the stomach, not difficult to distinguish from the lead colic to be described later. Usually the patient already exhibits at this stage general emaciation and marked pallor.