REFERENCES.
[ [1] Goadby, K. W.: A Note on Experimental Lead Poisoning. Journal of Hygiene, vol. ix., No. 1, April, 1909.
[ [2] Legge, T. M.: Report on the Manufacture of Paints and Colours containing Lead (Cd. 2466). 1905.
[ [3] Duckering, G. E.: Journal of Hygiene, vol. viii., No. 4, September.
[ [4] Meillère, G.: Le Saturnisme, chap. iv. Paris, 1903.
[ [5] Armit, H. W.: Journal of Hygiene, vol. viii., No. 5, November, 1908.
[ [6] Tanquerel des Planches: Traité des Maladies de Plomb, ou Saturnines. Paris, 1839.
[ [7] Stanski: Loc. cit.
[ [8] Gautier: Intoxication Saturnine, etc. Académie de Médecine, viii., November, 1883.
[ [9] Thresh, J. C.: The Lancet, p. 1033, October 7, 1905.
[10] Ibid., January 5, 1909.
[11] Thomason: Report of the Departmental Committee on Lead Manufacture: Earthenware, China, vol. ii., appendices, p. 61. 1910.
[12] Ibid.
[13] Dixon Mann: Forensic Medicine and Toxicology, p. 495. 1908.
[14] Oliver, Sir T.: Lead Poisoning (Goulstonian lectures). 1891.
[15] Schicksal: Die Bekämpfung der Bleigefahr in der Industrie, p. 38. 1908.
[16] Steinberg: International Congress of Industrial Hygiene. Brussels, 1910.
[17] Cloetta: Dixon Mann’s Forensic Medicine and Toxicology, p. 463.
[18] Little: The Lancet, March 3, 1906.
[19] Canuet, T.: Thèse, Paris, 1825, No. 202. Essai sur le Plomb.
[20] Drouet: Thèse, Paris, 1875. Recherches Experimentales sur le Rôle de l’Absorption Cutanée dans la Paralysie Saturnine.
[21] Manouvrier, A.: Thèse, Paris, 1873, No. 471. Intoxication par Absorption Cutanée.
CHAPTER III
SUSCEPTIBILITY AND IMMUNITY
A large number of poisonous substances, among which lead may be included, are not equally poisonous in the same dose for all persons. It is customary to speak of those persons who show a diminished resistance, or whose tissues show little power of resisting the poisonous effects of such substances, as susceptible. On the other hand, it is possible, but not scientifically correct, to speak of immunity to such poisonous substances. Persons, particularly, who resist lead poisoning to a greater degree than their fellows are better spoken of as tolerant of the poisonous effects than as being partially immune.
The degree of resistance exhibited by any given population towards the poisonous influence of lead shows considerable variation. Thus, in a community using a water-supply contaminated with lead, only a small proportion of the persons drinking the water becomes poisoned. There are, of course, other factors than that of individual idiosyncrasy which may determine the effect of the poison, as, for example, the drawing of the water first thing in the morning which has been standing in a particular pipe. But even if all disturbing factors are eliminated in water-borne lead poisoning, differing degrees of susceptibility are always to be observed among the persons using the water.
Lead does not differ, therefore, from any other drugs to which persons show marked idiosyncrasies. Thus, very small doses of arsenic may produce symptoms of colic in susceptible persons; a limited number of individuals are highly susceptible to some drugs, such as cannabis indica, while others are able to ingest large doses without exhibiting any sign of poisoning; and it is well known that even in susceptible persons the quantity of a particular drug which first produces symptoms of poisoning may be gradually increased, if the dosage be continued over long periods in quantities insufficient to produce marked symptoms of poisoning. In this direction a number of experiments have been performed with arsenic, particularly those of Cloetta[1], who found that the dose of arsenic for dogs could be gradually raised, if given by the mouth, to many times the ordinary fatal dose, but that if at this point a subminimal fatal dose was injected beneath the skin acute symptoms of arsenic poisoning followed.
We show in a later chapter that the excretion of lead in persons tolerant of the metal takes place through the medium of the bowel, and that probably those individuals who are engaged in what are recognized as dangerous processes in lead industries, and yet show no signs of illness, have established a kind of balance between the intake of the poison and its excretion by the bowel. It is rarely possible in such persons to find any lead excreted through the kidney. Occasionally, however, such persons, after working a considerable time in a dangerous lead process, become suddenly poisoned, and inquiry frequently discloses the fact that some disturbing factor, either intercurrent illness, alcoholic excess, etc., has occurred, or that the breathing of a big dose of dust has precipitated the symptoms of general lead poisoning. On the other hand, the experience of all persons engaged in the routine examination of lead workers is that, although a worker may show signs of lead absorption as distinguished from definite lead poisoning during the earlier period of his employment, he later shows less and less signs of the influence of the poisonous substance; even a mild degree of definite poisoning in the early stages of work in a lead process does not seriously militate against this gradually acquired tolerance, whilst careful treatment during such a time as the man is acquiring tolerance to the poison frequently tides him over the period, and enables him to withstand the ordinary dangers attached to his work.
The earliest symptom of lead absorption is anæmia. The anæmia is not very profound, and the diminution in the red blood-cells rarely reaches as low as 2,000,000 per c.c., the hæmoglobin remaining somewhere between 75 and 80 per cent. Some loss of orbital fat, as well as fat in the other parts of the body, occurs, but beyond this no obvious clinical signs of poisoning exist. Should such persons possess unhealthy gums, a blue line rapidly makes its appearance, but where the gums are healthy it is unusual to see any sign of deposit in this prodromal stage.
Persons who gradually acquire tolerance go through the stage of anæmia without exhibiting any symptoms of colic or paresis, and without any treatment the hæmoglobin and the number of red cells gradually pass back to a more or less normal condition. During this period—that is, whilst the blood shows signs of a diminution in its corpuscular and colour content—basophile granules may always be found if sought for, but disappear as a rule when the blood-count has returned to about 4,000,000 per c.c. and an 80 per cent. hæmoglobin. Such a man has now developed tolerance to the poisonous influence of lead, a tolerance which may be described as a partial immunity produced by recurrent subminimal toxic doses. On the other hand, in a number of persons who show definite susceptibility, the blood-changes are progressive, and do not show signs of automatic regeneration. In such persons, even after so short time as four to six weeks’ exposure to lead absorption, definite symptoms of colic may make their appearance. The removal of such an individual from the poisonous influence of lead generally clears up the symptoms in a short time, but the symptoms may occasionally continue for several months after removal from the influence of the poison. An individual of this type is to be looked upon as showing peculiar susceptibility, and should not be employed in any lead process where there is risk.
Such statistics as are available on this point show that an increased tolerance to the poisonous influence of lead is gradually acquired during periods of work, in that the number of attacks of poisoning diminish in frequency very considerably in relation to the number of years worked. As will be seen on reference to the chapter dealing with the statistics of lead poisoning ([p. 46]), the greatest number of cases occur in persons who have only worked a short time in lead. On the other hand, the sequelæ of lead poisoning only make their appearance, as a rule, after long-continued exposure. It is important to bear in mind that the various forms of paresis rarely make their appearance unless the subject has been exposed to long-continued absorption of lead, and, further, that the blood of such persons will as a rule show, on careful examination, evidences of the long-continued intoxication. If measures, therefore, were taken to determine the presence of such continued intoxication, and to diminish the amount of poison absorbed (subjecting the individual at the same time to a proper course of treatment), a large number of the cases of paralysis, encephalopathy, and death, incidental to the handling and manufacture of lead, could be eliminated.
Susceptibility may at times be shown by several members of one family. Oliver[2] says that he has known many members of one family suffer from and die of lead poisoning. In our experience several instances of this susceptibility have been noticed. In one case two brothers, working in one shift of men, developed poisoning, although no other persons in that shift showed any signs of it. A third brother, who came into the works after the other two had left, and who was placed under special supervision on account of the susceptibility exhibited by his two brothers, although given work which exposed him to the minimal degree of lead absorption, developed signs of poisoning six weeks after his entrance into the factory. In another factory, three sons, two daughters, and the father, all suffered from lead poisoning within a period of four years: the father had three attacks of colic, ultimately wrist-drop in both hands; one daughter had one attack of colic, and the other three attacks; whilst the three brothers all suffered from colic and anæmia, and one had early signs of weakness of the wrist. There was no evidence at all to show that these persons were more careless, or had been more exposed to lead dust, than any other of the persons with whom they worked, or that the work they were engaged upon was more likely to have caused illness to them than to other workers. Persons with a fresh complexion and red hair have been noted to be more susceptible to lead poisoning than dark-haired persons.
In one factory with which we are familiar, a number of Italian workmen are employed; these show considerably less susceptibility to lead poisoning than do their English comrades as long as they adhere to their own national diet. When, however, they give this up, and particularly if they become addicted to alcohol, they rapidly show diminished resistance; in fact, all the cases of plumbism occurring among the Italians in this factory during the last ten years have been complicated with alcohol. It is possible that the relatively large quantity of vegetables in the diet of these Italians influences the elimination of absorbed lead. There is some reason to suppose, however, that there may be racial immunity to lead poisoning.
The following case in the same factory illustrates a point already mentioned—namely, the gradually acquired tolerance to poisoning, and the unstable equilibrium existing. The individual was a man of twenty years of age. He commenced work on August 2, 1905. Six weeks later he was under treatment for seven weeks, for lead absorption, and had a peculiarly deep blue line round his gums, and a diminished hæmoglobin of 75 per cent. The symptoms disappeared with ordinary routine treatment, and his work was shifted to a position in the factory where he was exposed to the minimum amount of lead absorption, at which work he continued during the rest of the time he remained in the factory. He continued quite well until June, 1906, when he was again under treatment for two weeks, with the same blue line and anæmia, and his blood showed the presence of basophile granules. He was under treatment again in January and February, 1909, for five weeks, had again a deep blue line and basophile staining of his blood. On November 7, 1911, having had no anæmia and no blue line, he had a slight attack of colic. During this period of work his blood had been examined on eight occasions, and on each occasion it had shown basophile granules. The attack of colic was an exceedingly mild one. There is no reason to suppose that he had indulged in alcoholic excess, but there was some reason to think that for about a month he had been subjected to increased lung absorption. No other persons working in the same shift at the same work developed poisoning during the whole of this period. This case illustrates initial susceptibility, partial tolerance, and ultimate breaking down of such partially established tolerance.
During the experimental inquiry on lead poisoning by one of us [K. W. G.[3]], the question of the subminimal toxic dose and the minimal toxic dose was under consideration. Animals subjected to inhalation of lead dust invariably succumbed to the effects of the poison when the dose given represented from 0·0001 to 0·0003 gramme per litre of air inhaled, the period of inhalation being half an hour three times a week. On the other hand, when the lead content of the air was as low as 0·00001 gramme per litre, the symptoms of poisoning were long delayed, and in more than one instance, after an early diminution in weight, recovery of the lost weight took place, and the animals, whilst showing apparent symptoms of absorption, had no definite symptoms of paresis. These observations tend to confirm such clinically observed facts as are given in the case cited above, but they, of course, do not form a criterion as to the amount of lead dust which may be regarded as innocuous to man.
Lead is peculiarly a cumulative poison, and post-mortem analyses of viscera show that it may be stored up in certain parts of the body, more especially in the bone and red bone marrow and brain, and to some extent in the liver, spleen, and kidneys. Any circumstance, therefore, that temporarily interferes with the ordinary channels through which lead is excreted may determine the presence of a much larger quantity than usual of the metal in circulation in the body; and if in addition an increased quantity of the poison be inhaled, more or less acute symptoms follow. The localization of the deposit of lead is therefore of some importance.
Meillère and Richer[4] give an analysis of various organs of the body, but their results are not in accord with the majority of other observers. They found that the hair particularly contains a large quantity of lead. They do not seem to have examined the bones. Next to the hair, the liver seems to have contained the largest amount. Wynter Blyth[5] found 117·1 milligrammes of lead in the brain of a person who died of encephalopathy. In another case he found 0·6 gramme in the liver, 0·003 in the kidney, and 0·072 in the brain. Hougounencq[6] examined the organs of a person who died from lead poisoning, and found the largest amount of lead in the large intestine.
| Large intestine | 0·2150 | gramme. |
| Small intestine | 0·0430 | „ |
| Liver | 0·0050 | „ |
| Brain | 0·0008 | „ |
In the lung, stomach, kidney, and heart, only traces were found.
Dixon Mann[7] describes some experiments in which potassium iodide was given in cases of chronic poisoning, and during the whole of the experiments the fæces and urine were analyzed three times a week. He found by this means that a considerable amount of lead was being eliminated by the intestine. He therefore administered 2 grammes of lead acetate three times a day for five days to a patient, and he found that the fæces contained 0·1762 gramme the first day, 0·17411 gramme the second day; the fourth day it had fallen to 0·0053 gramme, and on the sixth day to 0·0006 gramme. The largest amount at any one time in a day obtained from the urine was only just over 0·001 gramme; the average amount found in the case of chronic poisoning was about 3 milligrammes, whereas the greatest amount at any one time in the urine was only 0·9 milligramme.
The quantity of lead present in the brain necessary to determine acute poisoning is not known, and it is probable that an extremely minute quantity will produce very serious effects; and in support of this may be quoted a number of observations in which search has been made for the metal in persons who have died of diseases affecting the brain associated with other symptoms of poisoning, and yet post-mortem examination of the brain by chemical methods has not revealed the presence of any lead whatever. In the case reported by Mott (see [p. 71]), no lead at all was recognized in the brain.
There are no reasons, therefore, for supposing that the immunity to lead poisoning depends on the fixation and storing up of the poisonous metal in a non-poisonous form in some special situation in the body, and, further, the particular situation in the body richest in lead in any given case of poisoning will depend rather on (1) the type of compound causing the poisoning, and (2) the portal through which such poisoning occurs.
The question of the detection of lead in the body is referred to in the [chapter] dealing with Chemical Examination. It is as well to point out in this connection that chemical investigation of the amount of lead present in the organs of persons dying from lead poisoning should, if possible, always be made where there is any doubt as to the diagnosis.
Certain observers—amongst them Gautier[8]—are of opinion that traces of lead may be found in normal persons. Thus, in a rat (Mus decumanus) Gautier found 2 milligrammes of lead in 60 grammes of liver. He considers that in many persons at least 0·5 milligramme of lead may be swallowed daily incorporated with the food, as a number of foods are liable to contamination by lead. Tinned foods, particularly those which are soldered up after the materials have been placed in the tin, certain tinned fruits with acid juices, often contain small masses of solder loose in the tins; in the case particularly of fruits the natural acid may slowly dissolve the lead from the solder. The amount of so-called “normal” lead, if it is to be found at all, must be very small, and would certainly be much smaller in the case of a normal person than in one who had been subject to definite lead poisoning. Such experimental evidence as is forthcoming supports the clinical observations that persons exposed to small doses of lead eventually develop tolerance of the metal, so that they may ultimately withstand many times the dose sufficient in the first instance to produce poisoning.
Such circumstances are the natural factors in the prevention of poisoning, and if due care be given to their significance, the surgeon in charge of any lead works may by judicious treatment and alternation of employment so assist and strengthen the natural defensive forces that susceptibility may be diminished, and the degree of tolerance increased to a very considerable extent. We do not imply that efficiency in the exhaust ventilation can be in any way relaxed; all we desire to emphasize is that certain natural defensive forces of the body do undoubtedly exist by which susceptible persons ultimately become less susceptible, and that by appropriate means these defensive forces may be augmented.
Susceptibility and immunity to poisoning by lead may be considered, according to the type of lead compound absorbed, further in its relation to age and sex. All compounds of lead are not poisonous in the same degree; the more easily soluble compounds are more poisonous than the less soluble. On the other hand, compounds which appear at first sight unlikely to produce poisoning may do so; for instance, fritted lead or lead silicate, a substance largely used in the potteries as a glaze, and manufactured by fusing together litharge and a silicate, would appear at first sight to be quite an innocuous substance. Owing to its method of preparation, however, it is not a pure compound of lead and silica, but contains lead oxide, metallic lead, etc., entangled in its meshes, and experimentally one of us (K. W. G.) has demonstrated that such a compound may be acted on by the tissues of the body, both when injected subcutaneously and even when inhaled, and so gradually produce definite symptoms of lead poisoning, but at a much slower rate than the more poisonous lead compounds. The fineness of division in which the compound of lead exists is another factor affecting its poisonous nature; the more finely divided particles find their way into the lung more easily than the coarser particles. Various subsidiary matters may also determine the susceptibility in a given individual, and of these a certain number require mention, as they probably act as definite predisposing factors. Age and sex may be regarded as predisposing factors to lead poisoning, and certain diseases also.
Age.
—Young persons are regarded as more liable to lead poisoning than adults, although it is difficult to obtain definite figures on the point, the duration of employment acting as a disturbing factor in estimating the susceptibility of young persons. They may have worked in a lead works for a year or more without showing any signs of poisoning, but develop them later in adult life, although it is very likely that absorption had taken place during the earlier period. In the Report of the Departmental Committee on the Use of Lead in the Potteries (Appendix XII.), the attack rate for the period 1899 to 1909 for young persons is 19·3 per 1,000, and for adults 18·8 for the same period, but the figures upon which these attack rates are based are too small to build any conclusion. The general clinical conclusions of appointed surgeons and certifying surgeons in the various lead factories would be, we believe, that the susceptibility of young persons is at least twice that of adults, and there is some ground for supposing that the tissues of an adult when growth has ceased more readily adapt themselves to deal with the absorption and elimination of poisonous doses of lead than do the tissues of a young person.
Sex.
—Women are more susceptible to poisoning by lead than men, and in lead poisoning from drinking water the proportion of women (especially pregnant women) and children attacked is stated to be higher than in men, and one such epidemic is quoted by Oliver where the rise in the number of miscarriages and premature births led to the discovery of the fact that the water-supply was contaminated with lead. The close relationship of lead poisoning to miscarriage has been repeatedly made out, especially by Oliver, in the white lead industry as carried on twenty years ago. Oliver also quotes the effect upon rabbits[9], Glibert upon guinea-pigs[10], and in the experiments of one of us (K. W. G.), referred to on [p. 99], all the animals to which lead was given during pregnancy aborted; and, further, with one exception out of eight animals, all died of lead poisoning, not as the result of the abortion, but some time later, although no further administration of lead was made. This confirms the well-known abortifacient effect of diachylon, and there is no doubt that the lead circulating in the maternal blood determines the abortion. Further, observers who have examined the fœtus in such cases have demonstrated the presence of lead in the fœtus itself. Oliver[11] found that eggs painted with lead nitrate did not hatch out, and on opening the eggs the embryos were found to have reached only a limited stage of development, and to have then died, whereas control eggs painted with lime produced live chicks. From what is stated later with regard to the curious action of lead upon the blood, the mechanism of abortion is easily understood; it is probable that placental hæmorrhages are produced, as in other organs of the body. But the effect of lead on the female is not only apparent during pregnancy. A considerable number of women working in lead processes suffer from amenorrhœa, and often from periods of menorrhagia and dysmenorrhœa, which as a rule is the more striking symptom. The effect of lead on the uterine functions, however, only exists so long as the constant intake of the poison is taking place, and many cases are recorded where women, after having had successive abortions while working in lead factories, have ultimately gone through a normal pregnancy and given birth to a living child. This circumstance bears a strong analogy to the similar train of events in syphilis.
In the Report of the Committee on the Use of Lead in the Potteries, some inquiry was made with regard to the possible association of lead absorption on the male side as a predisposing cause of infant mortality and premature birth. The tables given are not very conclusive, and from our own observations there seems to be very little evidence for supposing that a male lead worker is less likely to beget children, or that his children are more likely to be unhealthy than those of men working in any other industrial process. We are here speaking of the effect of lead under the conditions of its general use in this country now. In the absence of any precautions whatever as to daily absorption of dangerous dust, the effect on the offspring, even in the case of male lead workers, may well be evident, as has been shown by Chyzer[12] in the manufacture of pottery as a home industry in Hungary. One greatly disturbing factor in estimating the greater susceptibility of the female than the male in many lead industries is that the more dangerous work is performed by the women, such, for instance, in the Potteries, as the process of colour-blowing and ware-cleaning.
Predisposing Causes of Lead Poisoning.
—In lead poisoning, as in many other diseases, a number of predisposing and contributory causes may be cited which tend to lower the susceptibility of the individual to the poisonous effect of the metal and its compounds, or to so modify the functions of the body that a smaller dose of poison may produce more profound changes than would otherwise be the case.
Certain diseases may be regarded as predisposing causes by lowering the general resistance of the body tissues to the influence of lead, and a consideration of the chapter on Pathology will at once demonstrate how seriously certain diseases may contribute in this way.
The peculiar effect of lead is upon the blood and the walls of the bloodvessels, and it will therefore follow that any disease which may affect the intima of the bloodvessels may predispose to lead poisoning; and, further, as the elimination of lead takes place to a certain extent through the kidney, any disease which affects either the renal epithelium or the general maintenance of the excretory function of the kidney may predispose that organ to the irritative effects of the lead circulating in the blood. In the same way, the condition of lead absorption in which the balance of absorption and elimination of lead remains in such a ratio that no definite symptoms of lead poisoning appear may have that delicate balance easily upset by the introduction of some secondary cause, which, when operating in association with lead absorption, may precipitate symptoms attributable to poisoning by that metal. Chronic alcoholism especially, producing as it does definite changes in the kidney of itself—changes which it is impossible to distinguish by the naked eye from the effects of lead poisoning—must clearly act as a predisposing, if not even an exciting, cause of lead kidney infection. In experiments upon animals, it was found that the addition of alcohol to the diet of an animal which was the subject of chronic lead absorption precipitated the attack of definite poisoning; in other words, the latent period of lead poisoning—that is to say, the resistance exhibited by the tissues to the toxic influence of lead—was considerably diminished by this addition of a second irritant, alcohol. In several experiments, also, where the form of lead experimented with was one of the least toxic of the lead compounds, the animals subjected to such a compound alone did not become poisoned, but succumbed if alcohol were added to their diet. This experimental work is amply borne out by the clinical evidence of all persons who have had experience of industrial lead poisoning, as cases of colic and wrist-drop are frequently observed in lead workers shortly after alcoholic excesses. Individuals, therefore, who are suspected of the alcoholic habit should not be employed in any process where they are likely to run risk of absorption of lead dust.
Such diseases as syphilis and gout, by causing a heightened arterial tension or definite disease of the intima of the bloodvessels themselves, tend to weaken the arteries in much the same manner as does lead circulating in the blood, and must on that account act as predisposing causes.
In persons employed in lead trades some species of tolerance is generally developed, and if the functions of the body progress in the normal way the balance of elimination and absorption are equal, and, as will be seen later, the chief channel for the elimination of lead from the body is through the bowel. It follows, therefore, that any disease which tends to produce constipation or chronic inactivity of the normal intestinal functions will also tend to lower the resistance of the individual to lead poisoning.
Of the various types of intestinal disease of a chronic nature—such, for instance, as chronic dysentery, colitis, and the like—little need be said; but the predisposing effect of diseased conditions of the upper portion of the alimentary canal must not be overlooked, more particularly affections of the oral cavity itself. This special type of infection, often included under the term of “oral sepsis,” besides producing anæmia, is also a constant cause of intestinal disturbance, and as such operates as a particular predisposing cause of lead poisoning.
With regard to gout the evidence is not so clear. It was pointed out by Garrod[13] that gout was common among house-painters, and it has been generally stated that lead poisoning predisposes to this complaint. In the opinion of a considerable number of observers, however, gout is by no means common among persons working in white lead factories or lead-smelting works, but there seems to be some reason to suppose that it is somewhat common among those persons employed in the painting trades, but not among those employed in the manufacture of paints and colours. From the experiments carried out by one of us [K. W. G.[13]]. it seems probable that the occurrence of gout among painters may be associated with the use of turpentine, largely employed in the ordinary processes of painting, as this substance in particular is not one that is used by workers in other lead trades, and, from experiments performed on animals, the inhalation of turpentine vapour was found to produce very definite changes both in the kidney and the general metabolism of the body.
Malnutrition.
—Malnutrition is recognized as a predisposing cause of practically all forms of disease, and with a chronic intoxication, such as lead poisoning, malnutrition and starvation, with its attendant depression of all the vital forces of the body, is essentially a predisposing cause of poisoning, so much so that even the fact of commencing work without previously partaking of food may operate directly as a cause of poisoning. It has been found, moreover, experimentally by one of us [K. W. G.[14]] that an animal fed with milk containing lead nitrate did not develop poisoning, though the control animal developed well-marked symptoms of poisoning with a much smaller dose given in water.
Anæmia.
—Anæmia has already been referred to as occurring with great frequency in persons who are absorbing lead, and it usually forms one of the chief factors in the symptom-complex of lead cachexia. As the action of lead is particularly upon the blood and the hæmopoietic organs, diminishing the number of red cells and the amount of hæmoglobin, and impairing the organs from which fresh blood-cells are produced, a disease or state associated with anæmia other than of lead origin acts as a definite predisposing cause in the development of toxic symptoms in a worker in an industrial lead process.
Among the anæmias, two particular types may be referred to as of chief importance. In the first place, chlorosis, the anæmia occurring particularly in young women, is often associated with intestinal stasis. Lead anæmia occurring in a chlorotic person is always more severe than simple lead anæmia. Young persons suffering from chlorosis, therefore, should not be employed in a dangerous lead process until the anæmia has been treated. The second type of anæmia, which, from its frequency, may be also regarded as a predisposing cause of lead poisoning, is chronic secondary septic anæmia. Anæmias of this type, as was pointed out by William Hunter[15], resemble in many points the original idiopathic or Addisonian anæmia, often termed “pernicious anæmia,” and one of us has had occasion to inquire into the curious type of secondary anæmia associated with septic affections of the upper respiratory tract, particularly those related to chronic suppurative affections of the accessory sinuses of the nose, of the gums, of the mucous membrane of the mouth and the throat. The commonest forms of this secondary anæmia are those due to chronic post-nasal discharge, and to chronic infections of the gums and alveolus of the jaws, the latter often classed together under the term “pyorrhœa alveolaris.” This term is an exceedingly clumsy one, indicating a discharge of pus from the gum edges and sockets of the teeth, which are often loose. The disease commences as an infective gingivitis along the edges of the gum, and progresses to rarefying osteitis of the alveolar process, and often of the body of the bone. The affection rarely gives rise to pain, and as a rule the individual is entirely unaware that any chronic suppuration is present, and little or no notice is therefore taken of the disease. Progressive anæmia may thus be set up without any knowledge of its cause, partly by absorption of the actual bacteria and their products through the alveolar bloodvessels, and partly by the fact of the constant swallowing of pus and bacterial products, which set up various forms of chronic gastro-intestinal incompetence. From the discharges of the mouth, and issuing from the gum edges, numerous bacteria have been isolated, and in more recent work one of us [K. W. G.[16]] has succeeded in isolating and identifying certain bacteria as a direct cause of arthritis deformans, a malady occasionally, but without sufficient grounds, ascribed to lead poisoning. Arthritis of various types may occur in persons engaged in lead trades, but in all such cases we have had the opportunity of examining there has been some obvious source of septic infection, and no evidence that the arthritis was due to the action of lead. It is most important to draw the attention of those engaged in the protection of lead workers from the dangers of their occupation to these chronic septic conditions of the mouth, and it may be taken as a general rule that, wherever the blue line makes its appearance along the gums, such gums are in a state of chronic infection, and the appearance of the blue line is merely a secondary effect. It is exceedingly rare to find the blue line in persons with intact gums and clean teeth; and although attention is frequently drawn to the fact that a lead line exists in a person whose teeth are normal, little or no notice is taken of the presence or absence of a suppurative condition of the gum margins. Moreover, such a suppurative condition does not always result in obvious inflammation of the gum edges, and very considerable destruction of the alveolus and the interdental bone may exist without any obvious signs of its presence, unless the case be examined carefully with a fine probe. This particular point has been the subject of experiment by one of us. Animals exposed to the influence of air laden with lead dust never develop a blue line, although all the usual symptoms of lead poisoning make their appearance. When, however, some slight suppurative lesion of the gums was produced by an inoculation into the gum tissue of organisms isolated from a case of infective gingivitis in a human being, the site of inoculation and any suppurative lesion that resulted locally at once allowed the development of a blue line, and it was only in animals so treated that it was possible to produce experimentally the Burtonian line.
There is no doubt that any chronic septic infection may predispose to lead poisoning through the production of a secondary anæmia, and it is therefore inadvisable to pass for work in a lead process of a dangerous nature any persons suffering from an infected condition of the mouth. It follows also that the care of the mouth and gums should be rigorously enforced upon all persons employed in lead trades, as the mere mechanical facilities for the accumulation of débris around the individual teeth tends to increase the quantity of lead dust that may be retained in the mouth. This is gradually rendered soluble and absorbed, through the action of the bacterial acids which are always produced along the gum margins when any entangled food is retained in the interdental spaces.
One further point of importance attaches to the infections of the upper respiratory tract—namely, the constant ingestion of bacteria of a fermentative type. By this means the contents of the stomach may be maintained in a state of hyperacidity, and any small quantities of lead which become swallowed are thereby at once rendered soluble in the intermeal periods.
Of the other types of anæmia which may act as predisposing causes of lead poisoning, little need be said, as they are either associated with other grave symptoms or are rare in this country. But as all forms of anæmia, particularly septic anæmia, malarial fever, etc., are associated with destruction of the blood-cells, the presence of basophile staining granules in the red corpuscles of such persons is a constant feature, and must not be confounded with the basophile staining owing its origin to the effect of lead.
In addition to the diseases mentioned which may be said to predispose to lead poisoning, certain other diseases have been stated to be predisposed to by the action of lead. It is no doubt a fact that where chronic anæmia, wasting, loss of subcutaneous fat, decreased muscular power, and general lowering of the metabolic activity of the body, are produced, an individual so affected may be supposed to be more susceptible to certain infectious diseases, and among these stress has been laid on the alleged association of phthisis with lead absorption. This point is discussed in the [next chapter].
In summing up the difficult question of predisposition to lead poisoning, together with the correlated questions of susceptibility and immunity, certain facts may at any rate be clearly stated:
1. Undoubted individual susceptibility and immunity exist with regard to lead poisoning in exactly the same way as individual susceptibility and immunity may be shown to exist towards poisoning by many other metals and drugs. Therefore, given the same opportunities for infection, a person showing early signs of lead absorption may be regarded as susceptible.
2. Females are at least twice, and probably three times, as susceptible to lead poisoning as are males. Much of this susceptibility is determined by the extra stress thrown upon the female generative organs.
3. Certain diseases predispose to lead poisoning mainly by nature of the alterations in metabolism produced—chiefly anæmia.
4. Many persons engaged in lead industries become gradually tolerant of the absorption of lead, and in time resist much larger doses than would have been possible at the commencement of exposure, but in such persons the balance between absorption and excretion upon which that tolerance depends may become easily disturbed by intercurrent disease or sudden increase in absorption.