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.
REFERENCES.
[1] CLOETTA: Dixon Mann’s Forensic Medicine and Toxicology, p. 463.
[2] OLIVER, SIR T.: Diseases of Occupation, p. 142.
[3] GOADBY, K. W.: Departmental Committee on Lead Poisoning, etc., in
China and Earthenware Manufacture, Appendix No. XXV.
[4] MEILLÈRE AND RICHER: Meillère’s Le Saturnisme. Paris, 1903.
[5] BLYTH: Abstract of Proc. Chem. Soc., 1887-88.
[6] HOUGOUNENCQ: Meillère’s Le Saturnisme, p. 73.
[7] DIXON MANN: British Medical Journal, 1893.
[8] GAUTIER: Société de Biologie, April, 1903.
[9] OLIVER, SIR T.: British Medical Journal, May 13, 1911, p. 1096.
[10] GLIBERT, D. J.: Le Saturnisme Expérimental. Extrait des Rapports
Annuels de l’Inspection du Travail. Bruxelles, 1906.
[11] OLIVER, SIR T.: Diseases of Occupation, p. 139.
[12] CHYZER, A.: Des Intoxications par le Plomb se présentant dans la
Céramique en Hongrie. Budapest, 1908.
[13] GARROD: The Lancet, 1870.
[14] GOADBY, K. W.: Departmental Committee on Lead Poisoning, etc.,
in China and Earthenware Manufacture, Appendix XXV.
[15] HUNTER, WILLIAM: Severest Anæmias.
[16] GOADBY, K. W.: The Lancet, March 11, 1911.