The investigations of one of us (K. W. G.) on the experimental production of lead poisoning in animals has shown conclusively that the dust inhaled was far more dangerous, and produced symptoms far earlier than did the direct ingestion of a very much larger quantity of the same compound by way of the mouth and gastro-intestinal canal. There is no doubt whatever that the chief agent in causing lead poisoning is dust or fume suspended in the air. That a certain amount finds its way into the stomach direct is not denied, but from experimental evidence we consider the lung rather than the stomach to be the chief channel through which absorption takes place (see p. 81). The following table gives a specific instance of the incidence of lead poisoning in a white lead factory, and demonstrates clearly the ætiological importance of dust. The increase in reported cases, as well as in symptoms of lead absorption not sufficiently severe to prevent the individual from following his usual occupation, was associated with the rebuilding of a portion of the factory in which the packing of dry white lead had been carried on for a large number of years. The alterations necessitated the removal of several floors, all of which were thoroughly impregnated with lead dust. Before the alterations were undertaken it was recognized that considerable danger would arise; stringent precautions were therefore taken, and the hands engaged in the alterations kept under special observation. Notwithstanding this there was an increase in the number of reported cases, which were all mild cases of colic; all recovered, and were able to return to their work in a short time. TABLE I.--LEAD POISONING IN A WHITE LEAD FACTORY. The figures refer to the weekly examination of the whole of the men. For example, if a man was returned as suffering from anæmia on three occasions, he appears as three cases in Column 7. +-------+-------+-------+------+------+-------+------+------+------+ | | Total | Total | Cases| Cases| | | | | | | Number| Cases | in | in | | | | | | | of | of | Dusty| Other| Cases | Cases| Cases| | | | Exami-|Poison-| Pro- | Pro- |of Sus-| of | of | Blue | | Year |nations| ing |cesses|cesses|pension|Anæmia|Tremor| Line | +-------+-------+-------+------+------+-------+------+------+------+ | (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | |1905 | 5,464 | 9 | 8 | 1 | 20 | 78[B]|249[B]|311[B]| |1906[A]| 5,096 | 18 | 16 | 2 | 9 |256 |215 |532 | |1907 | 4,303 | 4 | 3 | 1 | 6 | 62 | 81 | 38 | |1908 | 3,965 | 4 | 3 | 1 | 5 | 40 | 25 | 11 | +-------+-------+-------+------+------+-------+------+------+------+ [A] Structural alterations in progress, including cutting up “lead floor,” saturated with white lead dust.