in such a way that the air from the first bottle must pass the whole of the water seals in each subsequent bottle. In the last bottle is dilute nitric acid saturated with sulphuretted hydrogen. If the series is now attached to an aspirating jar, and air drawn slowly over at the rate of ordinary respiration, the white lead powder in the first bottle being at the same time shaken so that the air is fully charged with finely powdered dust, lead is quickly detected in the air passing through the last bottle of the series, by the darkening of the solution. In this way the presence of lead dust has been demonstrated after passing through four 2-inch water seals and 8 feet of ¹⁄₄-inch wet rubber tubing. Such an experiment negatives the theory that all, or even a large quantity, of a finely divided powder becomes deposited on the upper portion of the respiratory tract. Particles of lead present in the air in industrial processes are exceedingly minute, and even in ground white lead the average size of the particle is under 1 μ. Finally, Tanquerel[6] and Stanski[7] succeeded in producing lead poisoning experimentally by blowing lead dust through a tube inserted in a tracheotomy opening. There remains, therefore, no room for doubt that the lung is the pre-eminent portal for lead absorption, particularly in industrial processes; from which it follows, as has been extensively shown in actual practice, that the diminution of dust in workshops and factories by means of exhaust ventilation is invariably followed by a diminution in the number of cases of plumbism. =Gastro-Intestinal.=--We have dealt with absorption by way of the lung, and have insisted that such inhalation of dust is of greater importance in giving rise to industrial lead poisoning than gastro-intestinal absorption. Gastro-intestinal absorption can take place, and is by no means negligible, in ordinary industrial conditions. One of the most interesting and important confirmatory evidences of the absorption of lead by the gastro-intestinal canal is to be found in the large outbreaks of poisoning in which water-supplies have been contaminated, either at their source or locally. We have already seen that electrolysis may play an important part in the solution of lead in water, and also learnt from Gautier[8] that the carbon dioxide content of water is not necessarily the sole predisposing element in the solution of lead. In this connection an important case is described by Thresh[9], where water by no means soft, but holding some 30 degrees of hardness, produced lead poisoning in an isolated family. The water in question was distinctly acid to litmus-paper, and contained a very high percentage of nitrates; the compound or salt of lead present was therefore one easily absorbed from the alimentary canal (see p. 86).