In 1853 the French government recorded its belief in the harmfulness of copper as a dietary constituent1 by the passage of a law (afterward repealed) prohibiting its addition to canned vegetables. Apparently the copper served for the maintenance of the green color of the vegetables, tho Johnson and Copeland2 suggest that it may have served a double purpose: "Copper sulphate is a powerful germicide. It has for years been added to canned meats and vegetables to prevent fermentation by bacteria and other organisms." For at least the last quarter of the nineteenth century, the belief in the germicidal action of copper was particularly flourishing. The early observations of its effect were made almost simultaneously on algae, fungi, and bacteria. During the years 1880 to 1883 Burq3 reported the results of an investigation, begun 30 years earlier, comprising a mass of data acquired by personal visits to all sorts of establishments engaged in the manufacture of copper and other metals, by extensive communication with the officers of workingmen's unions, working men themselves, proprietors of foundries, physicians, and mayors of towns where metal-working was the principal industry, by correspondence with English, Swedish, and Russian ambassadors, with the directors of Siberian mines, and with all possible individuals engaged in, or connected with, the mining and manufacture of copper?all of which led him to conclude that impregnation of the workmen with copper conferred on them a singular immunity to cholera. He found them equally immune to typhoid infection, and suggested that a similar immunity might exist toward diphtheria and smallpox. (These findings have been largely discredited as a result of more recent investigations.) In 1883 Walker4 published a monograph, written 20 years earlier, in which the verdict runs: "At all events the immunity of this class