Industrial poisoning from zinc is unknown. The chronic zinc poisoning among spelter workers described by Schlockow with nervous symptoms is undoubtedly to be attributed to lead. COPPER: BRASS _Occurrence of brass-founder’s ague._—Opinion is divided as to whether pure copper is poisonous or not. Lehmann has at any rate shown experimentally that as an industrial poison it is without importance. Occurrence, however, of brass-founder’s ague is undoubtedly frequent. Although neither pure zinc nor pure copper give rise to poisoning, yet the pouring of brass (an alloy of zinc and copper) sets up a peculiar train of symptoms. As the symptoms are transient, and medical attendance is only very rarely sought after, knowledge of its frequency is difficult to obtain. Sigel,[1] who has experimented on himself, believes that the symptoms result from inhalation of superheated zinc fumes. In large well-appointed brass casting shops (as in those of Zeiss in Jena) incidence is rare. Lehmann[2] very recently has expressed his decided opinion that brass-founder’s ague is a zinc poisoning due to inhalation of zinc oxide and not zinc fumes. This conclusion he came to as the result of experiments on a workman predisposed to attacks of brass-founder’s ague. Lehmann’s surmise is that the symptoms are due to an auto-intoxication from absorption of dead epithelial cells lining the respiratory tract, the cells having been destroyed by inhalation of the zinc oxide. He found that he could produce typical symptoms in a worker by inhalation of the fumes given off in burning pure zinc. _Metal pickling._—The object of metal dipping is to give metal objects, especially of brass (buckles, lamps, electric fittings, candlesticks, &c.), a clean or mat surface and is effected by dipping in baths of nitric, hydrochloric, or sulphuric acid. Generally after dipping in the dilute bath the articles go for one or two minutes into strong acid, from which injurious fumes, especially nitrous fumes, develop with occasionally fatal effect (see the chapter on Nitric Acid). Unfortunately, there are no references in the literature of the subject as to the frequency of such attacks. Recovery of gold and silver has been already referred to in the chapters on Mercury, Lead, and Cyanogen. Mention must be made of _argyria_. This is not poisoning in the proper sense of the word, as injury to health is hardly caused. Argyria results from absorption of small doses of silver salts which, excreted in the form of reduced metallic silver, give the skin a shiny black colour. Cases are most frequently seen in silverers of glass pearls who do the work by suction. Local argyria has been described by Lewin in silvering of mirrors and in photographers. III. OCCURRENCE OF INDUSTRIAL POISONING IN VARIOUS INDUSTRIES