Table IV. shows the severity of the attacks as stated by the surgeon, the number of attack, and the main symptoms. The personal element enters into the character of the reports, and symptoms which one surgeon might describe as slight another might regard as moderate, or even severe. In general, however, “slight” includes cases of (1) colic without complication, and of comparatively short duration; (2) anæmia in adolescence aggravated by employment; and (3) either of the above with tendency to weakness of the extensors. “Moderate” includes (1) a combination of colic with anæmia; (2) profound anæmia; (3) partial paralysis; and (4) cases in which there is constitutional debility. “Severe” includes (1) marked paralysis; (2) encephalopathic conditions—convulsions, optic neuritis, and mental affections; (3) grave undermining of the constitution associated with paralysis, renal disease, and arterio-sclerosis. The reports are made during the attack, and information is not received of the sequelæ which may supervene, except in the event of a later report as the result of fresh exposure to lead. Number of attack has reference to definite occurrence of disability. Transient attacks which have preceded the disabling condition have been usually disregarded. It was necessary to limit the number of attacks which might be regarded as indicating chronic plumbism, and all those included in Column 10 are either third attacks or cases of chronic lead poisoning. Among the main symptoms, the headings “Gastric,” “Paretic,” “Encephalopathic,” and “Rheumatic or Arthralgic,” represent fairly accurately the relative incidence of these in cases of lead poisoning in this country; those under the headings “Anæmia” and “Headache” are useful in comparing relative incidence on the two sexes, but they occur, probably, much more frequently than the figures would indicate; those under “Tremor” and “Other” are less valuable. Under “Other” are included “Gout,” “Nephritis,” or “Cerebral Hæmorrhage,” so that entry under this head indicates chronic, rather than mild, lead poisoning. The conclusions from the table are easy to draw, as, in general, the feature which causes severity of symptoms to be prominent leaves its mark also on “Number of Attack” and “Main Symptoms.” Thus, in the industries in which severe cases exceed the average (brass, plumbing, printing, file-cutting, tinning, glass-cutting, ship-building, paints used in other industries, and other industries), the chronic nature of the plumbism is markedly above the average, and some severe symptom, usually paralysis, is also above the average. An exception to this rule is china and earthenware, where severity is considerably below the average, but where, among men, the figures for chronic lead poisoning and paralysis are distinctly high. It will be seen, however, that the proportion of slight cases even in this industry is below the average. On the other hand, severity is below the average in smelting, white lead, red lead, litho-transfers, enamelling, electric accumulators, paints and colours, and coach-painting, and the symptoms in these industries are, in general, colic rather than high degree of paralysis; but in them a severe symptom which is above the average, in general, is encephalopathy. The explanation of these differences depends, we believe, on two factors: (1) Duration of employment, with which, naturally, the age of the worker is associated; (2) opportunity of inhaling lead dust. The longer the employment, the more likely, naturally, if absorption goes on, is the plumbism to become chronic, and to be associated with paralysis, its prominent sign. Duration of employment among males in file-cutting and china and earthenware, as contrasted, for instance, with that in white lead, is very much longer, and the same could be shown of comparatively new industries, such as electric accumulators and litho-transfers. Thus, in one year the age distribution and duration of employment of those attacked in three of these industries was as follows:

Persons employed in the manufacture of white and red lead, electric accumulators, paints and colours, and the others named, are exposed essentially to dust from salts of lead, which are readily absorbed. Poisoning, therefore, if precautions are inadequate, will quickly show itself, causing certain workers to seek other employment after one attack. Poisoning thus produced is more likely to induce colic, or, if the dose has been large or the individual markedly susceptible, encephalopathic symptoms, than paralysis. On the other hand, the slowness of the onset of symptoms in the case of brass workers, plumbers, printers, file-cutters, and tinners, is more the result of inhalation of fumes or of dust of metallic lead than of salts of lead; or if the inhalation be of salts of lead, then of these in less amount and over a long period, with, as a result, gradual undermining of the constitution, showing itself in paralysis, arterio-sclerosis, and renal disease. The two factors indicated obviously account for the differences in severity and number of attack between males and females. If second and third attacks are comparatively fewer in females than in males, it follows that, in general, the attack will be less severe also, and this is brought out in the figures. Cerebral symptoms—encephalopathy, to which headache may be added—are more than twice as frequent in females as males. This may be due to idiosyncrasy, but it may very possibly be simply the result of short duration of employment of young workers in processes where dust of salts of lead is incidental.

Attacks generally are most frequent in the first or second year of employment. Thus, of 2,195 attacks reported in the four years 1904 to 1907, as to which sufficient data are given, 898 occurred in the first two years of employment, and of these 672 occurred in the first year—that is, three-sevenths of all the cases were reported during the first two years, and four-sevenths in the whole of the remaining years of employment. It is, unfortunately, impossible to say what is the proportion of attacks among those employed for any given age period. In some factories—as, for example, lead smelting works—the average duration of employment is about thirteen years. The length of employment preceding an attack was made out from reports on cases which occurred in the white lead industry in 1898—a time when a number of new workers were taken on to replace the female labour abolished in June of that year, and conditions as regards removal of dust were entirely different from what they are now. The figures, therefore, can only be considered to have bearing upon incidence under almost the worst possible circumstances. Of 155 attacks, duration of employment was stated to have been less than 1 week in 3, from 1 week to 1 month in 8, from 1 to 3 months in 62, from 3 to 6 months in 44, from 6 to 12 months in 12, and 1 year and over in 26.

Attempt has been made to discredit the value of Section 73 of the Factory Act, 1901, on the ground that the proportion of cases in which some degree of paralysis is present is very high as compared with the extent found by other observers. The points we have laid stress on—(1) duration of employment, (2) varying kinds and amounts of lead dust and fumes—are, we believe, quite sufficient to account for, and give value to, the figures dealt with. To them should be added another factor, though one of less account—namely, the extent to which particular muscles are used. In the case of file-cutters, for instance, there is no doubt that the cramped position of the left hand holding the chisel, and the work thrown on the right in holding the heavy mallet, determine the direction of the paralysis, especially on to the muscles of the thenar and hyperthenar eminences and of the fingers.

There is, however, difficulty in deciding whether such entries on reports as “weakness of arms and legs,” “weakness of arms,” “muscular weakness,” etc., should be interpreted as incipient paralysis.[A] With a disease like lead poisoning showing marked tendency to affect the muscles supplied by the musculo-spiral and other nerves, the only safe course was to include all these terms as equivalent to partial paralysis. Table V. on p. 54 shows close parallelism for the six years.

If it is difficult to distinguish rightly all the cases classed as “paralysis,” it is even more difficult to determine what should be included under the term “encephalopathy.” We have limited it to epileptiform seizures, optic neuritis (uncomplicated by epilepsy), and various forms of insanity. Table VI. on p. 54 is interesting as showing how fairly constant the numbers are from one year to another.

Except in the one industry of earthenware and china, in which a return of the number of persons employed according to process and kind of ware has been made on three separate occasions, and in which the reports of the certifying surgeons enable the cases of poisoning to be classified in the same way, it is difficult to determine accurately the attack rate of lead poisoning. Even in the earthenware and china trade many things have to be borne in mind. The poisoning which occurs is not distributed evenly over all the factories. Thus, among the 550 potteries, in the years 1904 to 1908, five potteries were responsible for 75 cases, and 173 for the total number of cases (517), leaving 377 factories from which no cases were reported.

Table V.—Forms of Paralysis: 1904-1909.

Table VI.—Encephalopathy.

The same state of things is found in all the other industries. Particular factories, owing to special method of manufacture or special manner of working, may have an incidence out of all proportion to that prevailing in the trade generally. And it is, of course, control of these more obvious sources of danger by the efforts of manufacturers and the factory inspectors that has led to the notable reduction recorded—e.g., in white lead works and the pottery industry.

Returns of occupiers do not lend themselves readily to exact estimate of the number of persons exposed to risk of lead poisoning, as they do not differentiate the processes, and in nearly all factories in which lead is used some of those returned will not come into contact with it.

In industries, however, in which there is periodic medical examination of persons employed in lead processes an attack rate can be made out. It must be regarded as approximate only, as in the manufacture of electric accumulators, for instance, medical examination is limited to persons employed in pasting, casting, lead-burning, or any work involving contact with dry compounds of lead, whereas the reported attacks include a few persons engaged in processes other than those named.

Table VII.—Attack Rate from Lead Poisoning in the Year 1910 in Certain Industries.

As has been mentioned above, the accurate information we have of the numbers employed in the several processes in the earthenware and china industry enable us to use the figures for that industry to illustrate, what is certainly true of all other lead industries also, the fact of the relative greater degree of risk in one process than another.

The fall in the number of fatal cases attributed to lead poisoning, as is perhaps to be expected, seeing that the great majority are deaths from chronic lead poisoning, does not run parallel with the diminution in the number of cases. Thus, in the five years 1905 to 1909 the deaths numbered 144, as compared with 131 in the previous five years, although the cases fell from 3,761 to 3,001. We believe this is due to an increasing inclination to attribute chronic nephritis, and even (without sufficient justification in our opinion) phthisis and pneumonia, to lead poisoning on the death certificates of lead workers. Copies of all death certificates on which lead poisoning is entered as directly or indirectly a cause are received by the Chief Inspector of Factories. All of industrial origin are included in the return. Of a total of 264 which could be followed up, encephalopathic symptoms appeared on the death certificate in 38 (10·6 per cent.); Bright’s disease, cerebral hæmorrhage, paralysis, or chronic lead poisoning either alone or as a combination of symptoms closely connected, in 188 (71·2 per cent.); phthisis in 13 (5·0 per cent.); and other diseases, such as pneumonia, etc., in 25 (9·4 per cent.). Table IX. brings out the relative frequency in the several groups of industries, and, as is to be anticipated, the different average age at death when due to acute and chronic lead poisoning.

TABLE VIII.—LEAD POISONING IN EARTHENWARE AND CHINA WORKS

(China, Earthenware, Tiles, Majolica, Jet and Rockingham, China Furniture and Electrical Fittings, Sanitary Ware).

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.

TABLE X.—COMPARATIVE MORTALITY FROM SPECIFIED CAUSES AMONG MALES ENGAGED IN CERTAIN OCCUPATIONS: 1900-1902.