One of the chief objections to this view, apart from the experimental evidence, is that in those trades where metallic lead is handled, particularly lead rolling, very few hygienic precautions have ever been taken in regard to washing before meals, smoking, etc. Although in these trades the hands become coated with a lead compound (oleate), and the workers frequently eat their food with unwashed hands, thus affording every opportunity for the ingestion of lead, the incidence of poisoning is by no means as high or so pronounced in these occupations as in those giving rise to lead dust, such as the white lead industry, where special precautions are taken, and where the incidence of poisoning is always related to the dust breathed. =Respiratory Tract.=--In a report on the incidence of lead poisoning in the manufacture of paints and colours, one of us [T. M. L.[2]] in 1902 laid stress on the marked incidence of poisoning in the specially dusty lead processes. Following on that report special attention was given to the removal of dust by means of exhaust ventilation. With the introduction of precautionary measures, the incidence of poisoning underwent a marked decrease, this decrease being most definite in those industries where efficient exhaust ventilation could be maintained (see p. 47). Experience shows that cases of poisoning in any given trade or manufacturing process are always referable to the operations which cause the greatest amount of dust, and where, therefore, the opportunity of inhaling lead dust is greatest. The investigations of Duckering[3], referred to on p. 203, show the amount of dust present in the air in certain dangerous processes. His results clinch the deductions made from general observation, that dusty processes are those especially related to incidence of industrial poisoning. Ætiologically, therefore, the relationship of dust-contaminated air and poisoning is undeniable, and in not a few instances on record persons residing at a distance from a lead factory have developed poisoning, although not employed in any occupation involving contact with lead, aerial infection through dust remaining the only explanation. The actual channel through which the lead dust suspended in the air gains entrance to the body is, therefore, of especial importance; one of two channels is open--gastro-intestinal and respiratory.