Lead poisoning and lead absorption

It was thought that some light might be thrown on chronic intoxication produced by lead salts if direct experiment were made upon animals, resembling in the arrangement of such experiments, as far as possible, the industrial conditions under which human beings contract lead poisoning.

The animals chosen for the experiments were cats, as it is a fact of common knowledge that it is impossible to keep cats in lead works, particularly white-lead, because they rapidly become poisoned if allowed to stray about the works. The same holds good in the case of dogs.

From the statistics already given in Chapter IV., and from the remarks in the chapter on Ætiology, there was no doubt whatever that dust played a most important rôle in the production of industrial lead poisoning. In attempting, therefore, to copy the industrial conditions, it is essential to submit the animals experimented upon to infection by means of air in which lead dust is suspended. A large number of experiments have been carried out in the first place, by myself[1], and later in conjunction with Dr. Goodbody[2], and another series of experiments were also undertaken by myself[3]. Further experiments are still in progress in this and other directions.

1. Breathing Experiments

—First Series.—A. The animals experimented upon were placed in a large closed chamber at one end of which an electric fan was fitted in such a way that the air was kept in constant motion. The lead dust was introduced by means of a funnel through the roof in a definite quantity during timed intervals. By means of an aspirating jar and a tube inserted into the side, samples of air were withdrawn from time to time during the experiments, and submitted to chemical analysis to determine the quantity of lead circulating in the air. These samples were drawn off at the level of the animals’ heads. Great care was taken to eliminate any swallowing of dust by the animals during the experiments, by protecting their coats from the dust and carefully brushing them at the conclusion of each exposure.

Second Series.—B. In other experiments a chamber containing two separate compartments was constructed, and lead dust suspended in air was blown into the two compartments by means of an electric fan situated outside. The apparatus was so arranged that the draught of air from the fan passed through two separate boxes, in which the lead compound under experiment was kept agitated by means of small fans situated in the boxes and driven by a second electric motor. In this way two different samples of lead were experimented on at one and the same time, the air current driving in the dust through the two boxes being equal on the two sides; the quantity of dust was therefore directly proportional to the compound used. Samples of the dusty air were aspirated off and subjected to analysis, as in the first series. In this series of experiments the animals were so arranged that only their heads projected into the dust chamber during exposure.

2. Feeding Experiments.

—Feeding experiments were carried out by mixing a weighed dose of the lead compound experimented with, and adding this to a small portion of the animal’s first feed in the morning. It was found that unless the lead was well incorporated with the animal’s food it would not take the lead in the dry form; and in dealing with white lead and other dust, it was necessary to give the compound in a similar form to that in which a man would obtain it under industrial conditions, which of course precluded the use of a solution.

The amount of lead given by the mouth as a control to the inhalation experiments was from seven to ten times the dose which could be taken by the animal during its exposure in the cage, and the dose was given daily, and not every third day as in the inhalation experiments. All the compounds used in the inhalation experiments were given to animals by the mouth, the animals’ weights being carefully noted.

In a further series of feeding experiments a soluble salt of lead was added to the animals’ food (water or milk), the salt in this case being the nitrate. The quantity added was much smaller than in the dust experiments. 0·1 gramme was given daily.

3. Inoculation Experiments.

—As a further control to both the breathing and feeding experiments, the various lead compounds similar to those used in the other experiments were inoculated into animals. The insoluble salts gave some difficulty in the technique of injection, but by using a large needle, and making the suspension of the material in the syringe, the difficulty was overcome. The quantity of material inoculated varied; it was calculated in fractions of a gramme per kilogramme body weight, the quantity of fluid used being the same in all cases—namely, 10 c.c.—and inoculations were made subcutaneously and intramuscularly in the muscles of the back after previous shaving. In only one case was localized inflammation produced, and this was when the acetate was the salt employed.

None of the animals exhibited any signs of discomfort during the experiments from the presence of lead dust in the air; once or twice sneezing was noticed, but this was an uncommon occurrence. This point is of practical importance, as the lead dust contained in the air in white-lead and other factories is not of itself irritating to the mucous membrane of the lung. The animals subjected to this form of experiment were no doubt absorbing much larger doses of lead than are persons engaged in the manufacture of lead compounds.

The only ascertainable difference in the ultimate pathological lesions produced in animals, whether inhaling large quantities or minimal quantities of dust, was the rate at which the poisoning took place. In certain experiments it was found that the animals maintained a kind of equilibrium, much as do workmen engaged in dusty lead processes. It was found, moreover, that some animals showed a certain amount of tolerance to the effect of lead dust, in that their weights remained almost constant, but an increase in the quantity of lead present in the air immediately produced progressive diminution in the body weight; and as this diminution in the body weight approached to one-third of the animal’s initial weight, so symptoms of chronic poisoning supervened.

In addition to the animals inhaling lead dust over prolonged periods, certain other inhalation experiments were made for the determination of lead dust in the lung as opposed to the stomach. In the inhalation experiments proper, where the animals were exposed to inhalation every other day or every third day, for only an hour at a time, the quantity of lead present in the air was not very large, and it was thought essential to determine if, in exceedingly dusty atmospheres, any appreciable amount of lead could be found in the stomach. Ten animals were submitted to the inhalation of air heavily charged with various types of lead dust. The animal was exposed to the dust for an hour and a half to two hours; at the end of this time it was anæsthetized, and when the respirations had ceased, and the animal was dead, sulphuretted hydrogen was blown into the lung and into the stomach. The animal was then rapidly dissected and staining looked for. The tissues were further treated with acid and re-exposed to sulphuretted hydrogen gas. In one animal only out of the ten was any staining noticed in the stomach. In none of the others was any such staining found, but very definite blackening was found in the larynx, trachea, and macroscopically even in some of the bronchioles. Sections of the lung were further submitted to histological examination, and by means of micro-chemical tests with chromic acid and with iodine, and also by comparing sections of the experimental animals and animals which had not been subjected to lead dust inhalations, a very much larger quantity of material was found present in the lungs of the inhalation animals than in the normal animal. The dust was situated in the alveoli and the alveolar cells, and often in the lymphatics. On examining microscopically sections of the lungs of those animals exposed to graduated inhalation over extensive periods, a far larger number of blackened granules, dust, pigment, and other substances, was found than in similar sections of animals which were under normal conditions and had not been exposed to lead dust, although it is true such animals show a very fair proportion of carbon particles taken up by the lung tissue.

A further important fact was noticeable in animals Nos. 21 and 22 (see p. 101), which had been exposed to a low solubility glaze such as is used in the Potteries. Low solubility glaze is compounded with lead frit—that is to say, a lead glaze (or lead silicate) which has been finely ground. The particles of this substance are much larger than those of ordinary white lead, and in addition they are much more angular. Of three animals exposed to this glaze, one actually died of pneumonia (acute), and the other two suffered from some bronchial trouble, both of them showing distinct signs of pneumonic patches and old and chronic inflammation when examined histologically; whereas in none of the other animals exposed to white lead dust or to the high solubility glaze, which contained white lead as opposed to lead frit, no such pneumonic or fibroid changes were found. This point is of some pathological importance.

The inhalation experiments also throw some light on the quantity of lead necessary to produce poisoning. The animals in the inhalation experiments were exposed for varying periods, and constant estimations made of the lead present in the air. In a number of instances samples were taken from the cage air during the whole of the experiment, as rapidly as possible. The quantity of lead floating in the air was found to increase as the experiment progressed, although a large amount of the lead introduced was caught on the side of the cage and deposited on the floor.

In the later experiments the method of taking the samples continuously during the experiment was abandoned, and four samples only were taken, and the average recorded. A simple calculation will give the quantity of lead dust it would be possible for an animal to inhale during the whole of this period of exposure. The utmost tidal air in the case of a cat would be taken at 50 c.c. Taking the average, about 0·27 gramme of lead was inhaled during the half-hour of exposure.

Feeding Experiments.

—Twelve feeding experiments of various types are recorded. The method of experiment was as follows:

The compound under investigation was carefully weighed out each day (0·5 to 1·0 gramme), the substance being some of the same compound that was being made use of for inhalation experiments. In the case of the white lead it was found essential to mix it with the animals’ food; they were given white lead in a small amount of their food, and no further food was given for some little time after the dose of lead had been swallowed. Low and high solubility glazes were also made use of for feeding, and as a further experiment alcohol was given to the animals in addition to the previous course of lead inhalation or feeding, and the exposure to lead continued after the alcohol was given. In addition to high solubility glazes, white lead, and flue dust, a soluble salt of lead was also used, in one series the salt being the nitrate. 0·1 gramme was given daily; and it is these two nitrate animals (46 and 47) which showed distinct differences from the white lead and other feeding experiments. In one case the lead was given mixed with water, in the other mixed with milk. The animal which was fed with the nitrate dissolved in water developed encephalopathy, whereas the one in which the substance was mixed in milk exhibited no signs, though fed for a similar period. Both the animals increased in weight, which is an unusual effect in experimental lead poisoning. The question of the addition of milk, which apparently prevented the absorption of lead, is of very considerable importance, as it is highly probable, as has been pointed out with regard to the precipitation of lead by means of organic substances, that the albuminoid substances in the milk precipitate the nitrate already in a state of solution; and it may be argued from these experiments that mixing the white lead with the food would tend to prevent the lead having a toxic or deleterious effect, but even when the lead was given in the form of pills between meals no poisonous effect was noticed. Further, the quantity of white lead given was considerable, and it is highly questionable whether the quantity of lead so taken would be dissolved by the gastric juice excreted under normal circumstances in its entirety, as a very considerable quantity would pass onwards through the pylorus undissolved. Until the lead compound has become soluble it cannot react with the albuminoid constituent of the food. Ordinary dry white lead or litharge does not combine directly with albumin.

The majority of the experimental animals showed alteration in weight. The most important point which is brought out by these experiments, considering them from the point of view of inhalation, is the enormous quantity of white lead the “feeding” animals swallowed without producing any apparent symptoms. The quantities cited are the amounts given per diem, whereas in the inhalation experiments the animals were rarely exposed more than three days a week for an hour at a time (see table, p. 101). The quantity of lead, therefore, given by the gastro-intestinal canal was at least ten times as much, in many cases fifteen or twenty times as much, as could be taken by the other animals via the lung during inhalation, and yet these animals showed little or no susceptibility to poisoning when fed with white lead or other lead compounds, unless alcohol was given in addition.

An examination of the stomach after death showed, in the case of the alcoholic animals, distinct evidence of gastritis, and there is some reason to suppose that in such animals a degree of hyperacidity may have existed, thereby promoting the rate of solution of the lead.

The increased susceptibility to lead poisoning through the agency of alcohol is interesting. No. 6 received, in addition to its inhalations or period of exposure in the dusty air, 50 c.c. of port wine per diem. Symptoms of lead poisoning appeared a day sooner than in any other animal, and if we eliminate this experiment, as the dust (flue dust from blast-furnace) contained also arsenic and antimony, three days sooner than the litharge animal, and twenty-five days sooner than the other animals exposed to white lead dust. In addition, this animal was the only one which actually died during the period of experiment; all the other animals were killed at the end of two months and submitted to histological examination; but the animal which had received alcohol died with symptoms closely simulating lead encephalopathy in man. The predisposing action of alcohol is still further emphasized by the subsequent experiments with three animals exposed to white lead dust; one was exposed thirty-seven and the other thirty days before symptoms appeared, whereas when alcohol was given poisoning was apparent within twelve days, and after only four inhalations.

In the case of animals fed with white lead, one after eight months, and the other a year and a half, showed no signs of lead poisoning at all, while the weights remained constant. At the end of this time alcohol (50 c.c. of port wine) was added to the animals’ diet, and one month after the addition of alcohol to the diet, the dose of white lead being continued constant, encephalopathy ensued. In a second case the animal was started on alcohol in addition to the white lead. In a month it was showing signs of slight paresis. Again, an animal fed on a low-solubility frit consisting of ground-up lead silicate, showed no ill-effects after receiving a daily dose of this compound. At the end of this time alcohol was added to its diet, and six months later the animal developed symptoms of cerebral involvement, which continued at intervals until a fatal attack of encephalopathy at the end of a year. There is thus definite evidence to show that the addition of alcohol to the animal’s diet undoubtedly hastened and determined the appearance of lead poisoning, and this, taken in conjunction with the inhalation experiments previously cited, is very strong evidence of the increased susceptibility to lead poisoning produced by alcohol. This supersensitiveness to lead through the medium of alcohol is a matter of clinical experience to most persons who have had experience of industrial lead poisoning, particularly those who have been engaged in the routine examination of persons working in factories.

Inoculation Experiments.

—In order to control both the feeding and the inhalation experiments, and more particularly to obtain direct information of the effect of lead upon the body tissues, resource was had to the inoculation of the various lead compounds tested—namely: (1) White lead, (2) litharge, (3) lead frit. These three compounds are the three types of lead salt which are used in the Potteries, whilst white lead and litharge are the compounds causing industrial poisoning in the largest proportion of cases in other industries. As a further control, the more soluble lead salts were also made use of—namely, acetate, nitrate, and chloride—mainly for the purpose of establishing some standard of poisoning both in rate and dose.

Several rather unexpected results were derived from the inoculation experiments, which will be referred to.

The method of inoculation was to suspend the lead compound to be tested in normal saline solution or distilled water. The animal was then shaved, and the lead compound inoculated into the muscles of the back. The corrosive action of these lead salts was avoided by using a considerable quantity of diluent.

Lead frit is a constituent of low-solubility glaze—that is to say, a glaze which has not more than 5 per cent. soluble lead when subjected to the standard test of exposing 1 gramme of the glaze to a litre of 0·04 per cent. hydrochloric acid for an hour at room temperature. The frit which was the constituent of this glaze is produced by heating together litharge or lead and silica, the production being a yellow, hard, glaze-like material looking very much like sugar-candy. It is not by any means a compound of lead and silica of simple composition, as different samples show a wide variation in their lead content; whilst, in addition, the mode of its formation closely resembles that of an alloy or amalgam, and allows of the formation of a eutectic entangling in its meshes both of the constituents of which it is formed, so that a certain amount of free lead, in addition to the silicates of various descriptions, are present. At the same time the compound is highly resistant to the action of mineral acids, and, of course, much more insoluble and refractory than white lead, litharge, or other lead oxides. The body fluids, however, particularly the fluids in the subcutaneous and muscular tissue, definitely exert some action upon this fritted lead, and it was found experimentally that symptoms of poisoning could be produced in the experimental animals when even small doses were administered. A gramme of frit was inoculated, and in all but one case the animals showed definite signs of lead poisoning, and in two instances actually died with symptoms of encephalitis.

By washing the frit with distilled water, a slight diminution in the poisonousness was found, but by washing the frit with two or three changes of dilute acetic acid (3 per cent.), and then with distilled water, no pathological results followed inoculation. Water-washing frit alone definitely reduces the poisonous effect, but not to the same extent as the preliminary washing with acetic acid. On the other hand, washing with hot water had a much greater effect than cold-water washing.

Further evidence given by the inoculation experiments shows the relationship between the more soluble and the insoluble lead salts. The dose of acetate required to kill an animal was about 0·1 gramme of acetate per kilogramme body weight. On the other hand, 0·1 gramme of white lead produced no ill-effects, 0·5 gramme per kilogramme body weight produced death in about two months. In addition, those animals suffering from the more acute forms of poisoning developed definite eye changes and retinal hæmorrhages. Tortuosity and increased size of the retinal vessels were observed in several instances.

Besides controlling the experiments of feeding and inhalation, the inoculation experiments play a still more important part, as they furnish the correlation, necessarily, of the histological changes found as the result of poisoning by means of lead. In all the animals which have died of poisoning, certain definite trains of symptoms made their appearance. These symptoms were in practically all particulars similar to those observed in industrial lead poisoning in man, the onset of the affection and its clinical course corresponding to the symptom-complex in man, including those of cortical involvement, and often similar to the classical Jacksonian variety.

Throughout these experiments the animals exhibited no signs of irritation, and during the initial period, even, when loss of weight was a noticeable feature, their appetites remained exceedingly good; they were quite friendly, and purred loudly when stroked; but when symptoms of poisoning became manifest, particularly the onset of paralysis, a definite change in mental phenomena took place: the animals became quarrelsome, highly apprehensive of danger without cause, morose and lethargic by turns. At this stage, in more than one instance, acute encephalopathy supervened. The mental change was peculiarly striking in reference to Mott’s case, quoted on p. 71, as in all respects it was exactly analogous with the train of symptoms recorded in that case. To sum up, the symptoms produced in the experimental animals by the lead compounds inoculated and respired, no matter what the particular compound of lead experimented was, were as follows:

1. Slight preliminary rise in weight at the commencement of the experiment, lasting from one to two weeks.

2. Progressive loss of weight, mainly due to the disappearance of all fat, subcutaneous, kidney, mesenteric, etc., with associated anæmia, and the curious sunken and pinched faces commonly associated with saturnine cachexia.

3. Paresis of various types.

In the cat the muscles first affected are those of the back and the quadriceps extensor of the hind-limbs. The onset of the paralysis is slow and insidious, but may be acute; as a rule weakness in the muscles of the lumbar region and the spine are the first symptoms; secondly, inability to jump, owing to the weakness of the quadriceps extensor, while the animal tends to fall over when turning round quickly. Encephalitis occurs, and is frequently fatal. As a rule the affection is unilateral; complete loss of consciousness may occur, followed by slow but complete recovery. The animals gave no evidence of suffering pain, and, when recovered from an attack of encephalopathy, would at once take milk, but seemed dazed and uncertain in their movements. When the animals reached the stage of paralysis, they were destroyed under anæsthetics, and subjected to post-mortem examination. The post-mortem findings of a typical case were as follows:

The animal was emaciated, the fur easily pulled out, and the muscles were exceedingly flaccid.

Rigor mortis was slow in making its appearance; the blood remained fluid for a considerable time.

Practically no fat was to be found in the whole of the mesentery, and the omentum was devoid of fat and shrivelled. The fat around the kidneys had entirely disappeared. There was little orbital fat.

The peritoneum was thin and glistening, and very frail.

The whole of the mesenteric vessels, particularly in the region of the large intestine and the ileo-cæcal valve, were engorged with blood; whilst in the lower part of the small intestine, and often in the duodenum, occasionally in the whole of the jejunum and ileum, traces of minute hæmorrhages were found along the intestinal wall.

The liver was engorged with blood, as was the spleen.

The kidney capsule stripped easily, but was occasionally adherent here and there. The whole of the cortical vessels were injected with blood, the branching showing most distinctly.

A good deal of serous fluid was at times found underneath the kidney capsule.

On section the cortex appeared engorged with blood, and showed here and there, even to the naked eye, small hæmorrhages.

In the region of the appendix a few large mesenteric glands were invariably found, whilst a few glands might also be found in the wasted mesentery of the small intestine. In the region of the appendix the glands were frequently dark in colour. On opening the gut, minute hæmorrhages and ulcerated patches were to be found in the lower part of the ileum; the ileo-cæcal valve, and the whole of the large intestine, extending right up to the end of the appendix, was covered with a dark slate-blue slime, in which lead could be easily recognized by chemical processes.

Ulceration of the gastric mucous is uncommon, and only on one occasion were any hæmorrhages found. In the thoracic cavity the lungs were generally found to be emphysematous, and particularly in those animals subjected to inhalation of lead frit containing angular particles of lead glaze broncho-pneumonia was found.

The heart was flabby, and occasionally distinct roughening and thickening of the valves was seen.

Nervous System.—On opening the skull, hæmorrhages were frequently found at the base of the brain, occasionally situated over the surface of the cerebrum. Minute hæmorrhages were found often underneath the arachnoid membrane, but the largest hæmorrhages were always found at the base of the brain, and spreading down into the spinal canal along the medulla.

On removing the cord, minute hæmorrhages were found along the surface, irregular in distribution, and never very large. On section the brain and cord appeared normal.

Histology.

—A large number of sections were prepared from the animals developing symptoms of poisoning; the various tissues are described seriatim:

Muscles.—These appear to have undergone general fatty degeneration. The individual muscle fibres are indistinct in outline, and show irregular areas stained by hæmatoxylin. Some infiltration may be seen here and there between the muscle fibres, and minute hæmorrhages are occasionally detected, the chief appearance being that of general atrophy. The heart muscle shows similar degeneration, and the tendency of the sarcolemma to break down and stain irregularly is apparent. In many areas the muscle fibres stain poorly, if at all. Occasionally minute hæmorrhages are found, passing between the muscle fibres.

Liver.—The hepatic cells show varied degeneration; the vessels passing between the cells are engorged with blood, the cells being frequently much distorted from their general arrangement, and here and there completely obliterated by small areas of exudation as well as actual hæmorrhages.

Spleen.—The parenchyma shows masses of irregular spaces filled with recently-shed blood; the individual cells show a granular degeneration, with occasional basophile staining, the general appearance being one of chronic congestion. Here and there cloudy swelling may be seen.

Intestine.—Sections across the small intestine show atrophy of the intestinal wall, slight degeneration of the muscular coats, with infiltration and minute hæmorrhages.

Large Intestine.—Here similar minute hæmorrhages are found, in no case large enough to be seen by the naked eye. Areas of necrotic tissue are also seen in which considerable quantities of lead sulphide particles are found.

Lung.—Red or grey hepatization may be found, or a general appearance of broncho-pneumonia, where the dust used contained angular or insoluble substances. In animals subjected to prolonged inhalation, particles of lead could be demonstrated in the alveolar cells, and in the tissue beyond, either by staining with chromic acid or by means of iodine. Staining by sulphuretted hydrogen is not very satisfactory, as most animals resident in a large city show masses of carbon situated in various parts of the alveolar cells. If, however, a section be treated by means of iodine or chromic acid, and watched under the microscope during the process, the particles of carbon are easily differentiated from those of lead compounds.

Nervous System.—Sections of the brain and spinal cord, and of the nerve supplying the paralyzed muscles, all exhibited the same phenomena of minute hæmorrhages. In later cases some change in the cells is found, but as a rule, beyond a slight increase of the intracellular substance, little or no change is found in the cellular elements of the brain; but in the region of the surface minute hæmorrhages may be constantly traced, spreading over the surface of the cortex. In the cord, sections made in various situations failed to show any very definite degeneration, and little or no hæmorrhage was observed amongst the cells of the cord. Hæmorrhages could occasionally be seen on the surface.

In a number of animals the anterior crural nerves supplying the paralyzed quadriceps extensor muscles were examined carefully both for degeneration and for hæmorrhages. Very few degenerated nerve fibres were found, not more than would be accounted for by the minute hæmorrhages, which were found passing in between the nerve bundles, and here and there producing pressure on the nerve bundles themselves.

Kidney.—In the kidneys minute microscopical hæmorrhages, some of them quite large, were found in the cortex. The hæmorrhages are diffuse and irregular, and apparently due here, as in other situations in the body, to the breaking down of minute venioles rather than arterioles. In many cases the change is capillary. Parenchymatous nephritis may be seen, probably resulting from the transudation taking place from the vessel walls.

The chief view brought out in the histological examination of the various organs is one of capillary hæmorrhage. This phenomenon is not peculiar to lead poisoning, but, from the work of Moore of Liverpool[4], it would seem that all heavy metals, such as bismuth, mercury, not excepting iron, tend to produce a curious generalized yielding of the minuter vessel walls. Armit[5] has demonstrated a similar effect with nickel. The phenomena is, however, typically associated with lead poisoning, and may, we think, be regarded as the definite factor of chronic lead poisoning.

For the purposes of controlling the experiments of inhalation, two other series of experiments were undertaken. In one instance an animal was fed for two years on white lead; the animal was given 0·1 gramme per day, and this was increased up to 0·5 gramme, and ultimately 1 gramme. This animal exhibited no symptoms whatever of lead poisoning, and when it was killed, at the end of the time of experiment, showed no apparent lesion, with the exception of very marked staining of the colon and vermiform appendix. This staining of the large intestine and the appendix, the engorgement of the vessels, particularly of the omentum and mesentery, the enlargement of the lymphatic glands in the neighbourhood of the colon, ileo-cæcal valve, and appendix, suggest the absorption of lead in the upper part of the intestine, and its discharge or elimination into the large intestine. That lead is absorbed into the upper part of the intestine was demonstrated in the following manner:

An animal was anæsthetized, an incision made, and a loop of intestine pulled up and clamped off, a solution of lead chloride being run into the loop by means of a hypodermic syringe. The mesenteric vein passing from this loop of intestine was then carefully secured, a small opening made in it, and the blood collected drop by drop until some 40 c.c. had been collected, the time occupied being about three-quarters of an hour. The blood thus collected was submitted to chemical examination, and lead was demonstrated to be present. Lead therefore passes direct from the intestine into the portal circulation.

In only one of the feeding experiments with solid compounds of lead was any definite symptom of lead poisoning produced, and in this instance the compound used was dust collected from the flues of a blast-furnace. This dust was afterwards found to contain a considerable quantity of arsenic. The experiment cannot therefore be regarded as conclusive. With the more soluble salts of lead, however, such as the acetate, lead poisoning may be set up by means of lead administered via the intestinal canal: 1 gramme of lead acetate administered by means of a hypodermic syringe through a catheter passed into the stomach of a cat produced abortion in ten days, and death in three weeks. Four grammes of acetate produced a similar effect in a dog in four weeks.

The two following cases, in which both chemical and histological examination has been carried out on the tissues of persons who had been employed in occupations which rendered them exposed to absorption of lead, and who died with symptoms directly suggestive of lead poisoning, may be added, as they confirm the experimental results given above in all particulars:

Case 1.—A woman aged twenty-one, employed in a litho-transfer works, who died after a short illness during which the chief symptoms were headache and mental clouding.

At the post-mortem examination no pathological lesions were discoverable with the exception of a small gland which had become calcareous, situated near the right bronchus. The brain was injected over the left cerebral hemisphere, but no hæmorrhages were to be seen with the naked eye. There were no other pathological signs. A portion of the brain showing the injection and congestion were submitted to histological and chemical analysis. Histologically the brain tissue was found to be normal, with the exception of slight chromatolysis of some of the larger cells; but interspersed about the whole section in the slides examined, but more particularly in the area of the cortex, minute microscopical hæmorrhages were found (see Fig. 3). Here and there these hæmorrhages were seen related to the expanded capillaries, all of which showed considerable engorgement with blood. The arteries and veins themselves were, in addition, considerably distended. There was no interstitial degeneration of the neuroglia noticed. A few patches were found which apparently represented old hæmorrhages undergoing gradual fibroid degeneration. In no case were the hæmorrhages of a size that could be detected by the naked eye.

Two hundred and fifty grammes of the injected area of the brain were submitted to chemical examination by the moist process described in the chapter on Chemical Analysis. The nitric acid filtrate from the electrolytic deposition gave a well-marked precipitate with sulphuretted hydrogen, which was filtered off and recognized as lead. There was only the merest trace of iron present. By colorimetric estimation the quantity of lead found present in the brain estimated as Pb was 0·0143 gramme. The quantity found in 250 grammes of brain substance examined from the injected area was 0·0041 gramme.

Case 2.—A man who had been employed in an electrical accumulator works for a considerable time, and who had had a history of several attacks of lead colic and one of lead paresis affecting both hands.

The man’s work in connection with lead ceased from the time of the paresis, but some three years subsequently he died with cerebral hæmorrhage.

Portions of the organs, brain, kidney, liver, and spleen, were examined histologically, stained in the ordinary way with hæmatoxylin and eosin. In the brain the same marked microscopical hæmorrhages were observed as described in the previous case, and in addition many more areas of old fibroid scars, very minute, but apparently corresponding to earlier minute hæmorrhages. The kidney showed definite interstitial hæmorrhage (see Plate III., Fig. 2), as did the liver and spleen.

A portion of the brain was further submitted to chemical examination, and 0·0014 gramme of lead was determined as present.

The importance of this confirmatory evidence is undoubted, as the presence of the capillary hæmorrhage existing in the tissues of a person dying under suspicious circumstances when employed in a lead process is confirmed by the chemical determination of lead in the tissues.

The following tables, arranged under three headings, give some of the experimental results obtained by submitting animals to the effect of compounds of lead.

Table XI. gives the inoculation experiments.

The materials used in these experiments were those used in the inhalation and feeding experiments. The experiments are also arranged in such a manner that each series is a control one of the other.

The amount of substance used for the inoculation gives some rough idea of the dose required to produce poisoning in an animal; but even this question of dose in absolute quantities, administered hypodermically, shows considerable variation in the degree of poisonous effect. The first animal in Table XI. was inoculated with acetate, this being one of the more soluble lead compounds, and was given it in three small doses. The animal received 0·3 gramme per kilogramme of body weight, whereas in No. 35 2 grammes of washed frit—that is to say, lead glaze formed by fusing together litharge and silica—actually did produce symptoms, but of a mild nature. Animal No. 33 only had 0·16 gramme, being 0·05 gramme per kilogramme of body weight; and this caused acute symptoms. 0·35 gramme of white lead in a 3·500 kilogramme animal (No. 31) produced no symptoms at all. In the list of the inoculation experiments, three animals only exhibited no symptoms—one of these (No. 31) which was given white lead hypodermically, and Nos. 41 and 42, which were inoculated with lead silicate or lead frit, which had been previously treated with acetic acid or water.

Several practical points arise from these experiments, notably with regard to the frits, as it is seen that a considerable amount of the toxic properties contained in frit are removed by washing—most by washing with acetic acid and water, but also to some extent by washing with hot water alone, showing that in the ordinary production of lead frit for pottery purposes a certain amount of lead in a soluble condition as regards the body tissues was still present. This is no doubt entangled in the true silicates in the forms of oxides, or even as carbonate. Further, the toxicity of the lead compounds used may certainly be arranged in the order of their solubility with regard to the animal tissues, the acetate being the most poisonous, and the frit, when washed, the least; but unwashed frit, even in relatively small doses, may produce poisoning. This point is still further emphasized in Table XIII. Animal No. 42, four months after previous inoculation, showed no signs of poisoning. Lead nitrate in water was therefore given in quantities of 0·01 gramme per diem; one month later this animal developed poisoning.

Table XII. deals with the feeding experiments.

In these experiments acetate was given in one case only, and then in the form of pills coated with keratin. It is impossible to say, however, whether the animal ever received any soluble lead, as on one or two occasions the keratin pills passed right through the animal without dissolving. On the other hand, feeding with nitrate of lead in water produced symptoms, but when the nitrate was given in milk no symptoms appeared. It will be noticed it took a cat four months to show any signs of poisoning taking 0·1 gramme per day; whereas the animal receiving subcutaneous doses of 0·16 gramme of acetate showed paralysis in fifteen days, and in twenty-two days was so ill that it had to be destroyed under an anæsthetic. The same relationship in time also obtains in the case of the animals fed on dry white lead. In practically no instance did definite or severe poisoning follow the feeding on dry white lead alone, even when quite large quantities were taken. On reference to the inoculation experiments of Table XI., it will be seen that the inoculation of 2 grammes of dry white lead produced definite symptoms, although the feeding cats had an amount very largely in excess of this. The only animals fed on white lead or frit exhibiting signs of lead poisoning were those which were given alcohol in addition to the lead compound.

A comparison of the results given in Tables XI. and XII. shows that animals which received lead compounds subcutaneously suffered much more than the animals which received the lead via the gastro-intestinal canal, even when the doses given via the mouth were exceedingly large. It will follow, then, that the actual contact with the more intimate fluids of the body, rather than the digestive juices, determines the solubility and general distribution of the lead compound in the body. This is confirmed by a recent paper by Straub[6].

The animals experimented upon by feeding were kept in the laboratory under the same conditions as the inhalation animals, but were so placed that under no circumstance could they obtain any lead dust by inhalation. These animals were used as control to the breathing experiments, the substance fed to the animals being in all cases the same substance as was used for the various inhalation experiments; but in addition a certain number of the animals were given alcohol, which are referred to in Table XII. Alcohol was also given to animal No. 6 in the inhalation series.

The animals fed with lead were fed with the same compound which was used for the inhalation experiments, 0·4 to 1 gramme being given daily; so that during the period these animals were exposed to lead dust the other animals were taking the same compound via the intestinal canal, but in much larger quantities, and yet they exhibited no signs of lead poisoning.

TABLE XI.—INOCULATION.