In classifying causes of death, the general rule should be to select, from the several diseases mentioned in the certificate, the disease of the longest duration. Exceptions to this rule are that definite diseases ordinarily known as constitutional diseases should have preference over the other diseases mentioned. After thirty-five years of age, certificates of death from lead poisoning are almost always filled in in association with other diseases which are the usual causes which lead to mortality generally. But neither phthisis, nor pneumonia, nor any acute disease of the heart or lungs, nor valvular disease of the heart, nor, indeed, any acute febrile condition, can have direct relation with--_i.e._, be a sequela of--lead poisoning. REFERENCES. [1] Annual Reports of the Chief Inspector of Factories since 1898, especially for 1909, p. 19. [2] Supplement to the Sixty-fifth Annual Report of the Registrar-General on the Mortality in Certain Occupations in the Three Years 1900, 1901, 1902, by Dr. John Tatham, pp. cxix-cxxii, Cd. 2619. CHAPTER V PATHOLOGY The pathology of lead poisoning has formed the subject of scientific inquiry from the time that the association of certain pathological symptoms was definitely correlated with poisoning by means of the metal or its salts. Acute poisoning, due to accidental swallowing of large doses of lead salts or to use of lead salts criminally, generally produces a train of symptoms different from those met with in chronic industrial poisoning. But it is difficult to understand why so many writers upon the subject of lead poisoning should have attempted to draw a hard-and-fast line between the pathological symptoms in acute and chronic poisoning. This is especially the case when the after-history of cases of acute poisoning is traced, for in a large number of instances a case of acute poisoning drifts on into a subacute, and finally a chronic, stage. All the symptoms of paralysis, encephalopathy, and even kidney degeneration, have been described in persons who were first of all the subjects of acute poisoning. The direct effect of a lead salt, such as the acetate, upon the mucous membrane of the stomach, is a caustic one, and the attention of observers seems to have been focussed on what is really a secondary effect of the lead salt, and not one intrinsically associated with actual poisoning by the metal itself.