Lead poisoning and lead absorption

by Sir Thomas Morison Legge; Kenneth Weldon Goadby

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.