Other conditions which might readily be admitted as sequelæ are optic neuritis, following on an attack of encephalopathy. No general statement can be made in regard to mental and nervous diseases, gout, pernicious anæmia, as sequelæ, as each must be considered in relation to the evidence adduced in the particular case, and after exclusion, in the first two, of syphilis as a cause.
The distinction between causation and association has to be borne in mind before admitting as sequelæ of lead poisoning diseases of bacterial origin, such as phthisis or pneumonia, or any disease to which the affected person may be thought to have been rendered more prone by reason of lead employment. The contention that a person may have been debilitated by lead poisoning is no proof that the enfeeblement of the constitution was the cause either of the bacillus gaining entrance into the lung or of the ultimate fatal issue from the engrafted disease. Such assertion in every case must rest on supposition. Evidence that lead employment predisposes to phthisis is not necessarily made stronger, in our opinion, by existence during life of clinical symptoms, or, in their absence, of detection of lead in the tissues post mortem.
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.