The statistical evidence from death certificates published in the decennial supplements of the Superintendent of Statistics[2] is of significance, not only in enabling comparison to be made between one industry and another, in regard to mortality from lead poisoning, but also in determining the other causes of death most frequently entered on death certificates of lead workers, and therefore, if they are in high excess, as compared with male workers generally, they are to be ascribed with some degree of certainty to deleterious effects of lead on some of the principal organs. Thus, in [Table X.] a list of occupations is given in which the mortality from plumbism in the years 1900 to 1902 was double or more than double the standard. It represents the mortality which would occur if the male population in the particular industry had exactly the same age population as that of “all males.” Further, the annual mortality among “all males” is taken as 1,000, and that of males engaged in the several industries is stated as a proportion of this. This “mortality figure” of 1,000 is made up of the mortality from various causes (of which only those considered to bear upon lead poisoning are given in the table) in the proportion stated.
The contention that, because lead workers die from certain diseases more frequently than “all males,” such diseases must be the sequelæ of lead poisoning is untenable unless other recognized causes of the diseases in question have been excluded. For excess of deaths from phthisis and respiratory diseases the conditions of work and exposure to inhalation of mineral and metallic dust or vitiation of atmosphere, in pottery, spelter, printing works, and file-cutting workshops, sufficiently account. The figures, indeed, take no account of this, and their value, in some at any rate, is still further diminished by the very large number of occupations (several involving no contact at all with lead) included in the headings. With exception of the strikingly greater proportion of deaths among lead-workers from Bright’s disease, the figures are too contradictory to draw deductions from as to what are “sequelæ” of lead poisoning. But this figure—160, as compared with 35 for all males—is confirmatory evidence, if any were needed, that chronic Bright’s disease is a sequela. And, from the pathology of lead poisoning, we believe that the granular condition of the kidney is due to the sclerotic change brought about in its substance by microscopic hæmorrhages. We have very little evidence indeed in man that this interstitial change is set up or preceded by an acute tubal nephritis. While we do not deny that there may be some parenchymatous change associated with lead poisoning, we do not believe that it is of the kind which gives rise to the large white kidney, and we should therefore exclude such disease as a sequela. But if chronic Bright’s disease is admitted, the train of symptoms associated with it—notably arterio-sclerotic changes resulting in cerebral hæmorrhage and albuminuric retinitis—must be admitted also. Unless it were established that granular nephritis were present in a lead-worker before commencement of lead employment, we think it would be useless to endeavour to prove that the condition was independent of lead, despite its comparative frequency as a cause of death apart from employment.
TABLE IX.—MAIN SYMPTOMS APPEARING AS THE CAUSE IN 264 DEATH CERTIFICATES OF LEAD POISONING.
| Industry. | Encepha- lopathy. | Bright’s Disease. | Cerebral Hæmor- rhage. | Paralysis. | Lead Poisoning. | Phthisis. | Pneumonia, Bronchitis, Heart Failure, Colic, Hernia, and Aneurism. | Total. |
|---|---|---|---|---|---|---|---|---|
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) |
| Smelting of metals | 1 | 6 | — | 3 | 5 | 1 | 1 | 17 |
| Brass works | — | 3 | — | 1 | 1 | — | 1 | 6 |
| Sheet lead and lead piping | — | 1 | — | — | 1 | — | 1 | 3 |
| Plumbing and soldering | 2 | 3 | — | 1 | 2 | 1 | 2 | 11 |
| Printing | 3 | 3 | — | 2 | 5 | 1 | 3 | 17 |
| File-cutting | 1 | 11 | 2 | 2 | 2 | 1 | — | 19 |
| Tinning and enamelling | — | 1 | — | — | 1 | — | — | 2 |
| White lead | 13 | 2 | 2 | 4 | 2 | 1 | 3 | 27 |
| China and earthenware | 8 | 24 | 14 | 3 | 6 | 2 | — | 57 |
| Glass-cutting | 1 | 6 | — | — | 1 | — | 1 | 9 |
| Electric accumulators | 2 | 1 | — | 1 | — | — | 2 | 6 |
| Paints and colours | 4 | 1 | — | — | 2 | 1 | 3 | 11 |
| Coach-making | 1 | 8 | 5 | 6 | 10 | 3 | 4 | 37 |
| Ship-building | 1 | 4 | 1 | — | 1 | 1 | — | 8 |
| Paints used in other industries | — | 3 | 1 | 4 | 6 | 1 | 2 | 17 |
| Other industries | 1 | 2 | 1 | — | 11 | — | 2 | 17 |
| Total | 38 | 79 | 26 | 27 | 56 | 13 | 25 | 264 |
| Average at death | 32 | 43 | 47 | 43 | 44 | 38 | 40 | — |
TABLE X.—COMPARATIVE MORTALITY FROM SPECIFIED CAUSES AMONG MALES ENGAGED IN CERTAIN OCCUPATIONS: 1900-1902.
| Occupation. | Causes of Death. | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| All Causes. | Alco- holism. | Gout. | Phthi- sis. | Diseases of the Nervous System. | Diseases of the Circu- latory System. | Diseases of the Respi- ratory System. | Diseases of the Diges- tive System. | Bright’s Disease. | Other Diseases of the Urinary System. | Plumbism. | Acci- dent. | |
| (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) | (11) | (12) | (13) |
| All males | 1,000 | 16 | 2 | 186 | 105 | 145 | 174 | 57 | 35 | 17 | 1 | 59 |
| Printer | 994 | 8 | 3 | 300 | 111 | 125 | 131 | 55 | 42 | 15 | 2 | 21 |
| File-maker | 1,700 | 14 | — | 387 | 225 | 198 | 325 | 78 | 134 | 26 | 56 | 46 |
| Copper-worker | 1,090 | 7 | 3 | 162 | 104 | 139 | 357 | 45 | 24 | 21 | 3 | 51 |
| Lead-worker | 1,408 | 38 | — | 165 | 134 | 222 | 309 | 14 | 160 | — | 102 | 52 |
| Coach-maker | 824 | 4 | 4 | 129 | 113 | 129 | 150 | 46 | 39 | 14 | 8 | 29 |
| Earthenware | 1,493 | 8 | — | 285 | 131 | 219 | 473 | 57 | 33 | 20 | 10 | 33 |
| Glass | 1,260 | 7 | 4 | 283 | 131 | 177 | 268 | 54 | 58 | 16 | 8 | 31 |
| Painter and plumber | 1,114 | 13 | 8 | 213 | 133 | 105 | 168 | 31 | 74 | 20 | 23 | 50 |
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.