2. Mode Of Operation

There can be little doubt that the preparations of lead operate by direct contact with the parts affected, being in the first place absorbed into the blood, and then distributed over the system. By Tiedemann and Gmelin, Orfila, and other chemists, the metal has been detected in the blood, the urine and milk, the brain and spinal marrow, the muscles, the bones, the liver. spleen, and kidneys, and in the coats of the stomach, bowels, and gall-bladder. As it exists in the tissues, it is sometimes not discoverable by the ordinary tests; incineration being necessary bo break up the combination in which it is probably held with organic matter. The precise character of this combination, whether in the blood or the solid tissues, is unknown. The system has in general the power of throwing off the poison sooner or later, unless in quantities sufficient to destroy life. It is eliminated by the kidneys, skin, mammae, and probably by the various secretory organs which empty into the alimentary canal. How long it may remain in the system is not certainly known; but it was found by Orfila in the liver, intestinal coats, and bones of an animal, eight months after it was administered. (Med. Times and Gaz., iv. 279.) It may operate through the susceptibilities of the parts with which it is brought into contact; but there is reason to think that it sometimes at least enters into elementary combination with the tissues, and thus necessarily modifies their action. (See Arch. Gen., 4e ser., xxvii. 75.) It is probably through its presence in the substance of the nerves themselves that it occasions neuralgic pains, and at length loss of power, both sensory and motive. Colica pictonum is a combination of neuralgia and partial palsy of the bowels; and thus the internal correspond exactly with the external effects of the poison.

* The influence of the poison, in cases of pregnancy, besides causing abortion, is said either directly or indirectly to extend to the foetus, leading to arrest of development and even death, and, when these results are avoided, causing various morbid conditions in the infant. Thus, of six cases of pregnancy accompanied with lead-poisoning, observed by M. Constantin Paul, three of the offspring perished in the first six months, and of the three which remained, one was epileptic, one scrofulous, and the third only two months old, so that time had not been allowed for the development of morbid tendencies. (Arch. Gen. de Med., Mai, 1860, p. 530.) In 123 cases of pregnancy, there were 64 abortions, 4 premature deliveries, 5 still-born, 20 infants who died in the first year, 8 in the second, 7 in the third, 1 later, and 14 living, of whom only 10 were more than three years old. (Ibid., p. 532.) M. Paul also states, as the result of his observation, that lead-disease in the father, as well as in the mother, serves as the cause of the death of the foetus, and the premature death of the infant. (Ibid., p. 516.) - Note to the third edition.

The chief avenues through which lead enters the system are the alimentary canal and the lungs. The skin, and the mucous membranes of the eyes, mouth, and nostrils, may possibly admit its passage in small proportion; but, with the epidermis sound, it is doubtful whether it ever enters through the skin in quantities sufficient to produce poisonous effects. It is very often applied to the surface of the body largely, and for a long time consecutively, even in its most soluble forms, without any observable general effect. When applied to excoriated surfaces and ulcers, it is said sometimes to have occasioned serious lead-poisoning; though I have never witnessed a case of the kind. The particular part upon which it may first display its effects, and the rapidity of its operation, depend in some measure upon the surface of application. Thus, when taken into the alimentary canal, it may be interred to be more likely to occasion colica pictonum than through any other avenue; but it must be allowed that positive proof to this effect is wanting. It probably acts most readily and rapidly through the respiratory organs. The late J. Price Wetherill, who was long and largely engaged in the manufacture of white lead, informed me that the workmen in his employ, most liable to be poisoned, were those engaged in preparing the thin sheets of lead used in the process. The operation exposed them constantly to the fumes of the melted metal. It is, moreover, well known that painters are more apt to be attacked when they use oil of turpentine in mixing the white lead, than when they employ fixed oil alone; the terebinthinate vapours, in the former case, carrying a portion of the lead with them into the lungs.*

The persons most exposed to the poisonous influence of lead, are those engaged in the diiferent manufactures and arts in which the metal is concerned Miners and smelters of lead, manufacturers of white lead and other preparations of the metal, painters, plumbers, etc., are apt to be affected.+ The poison is frequently taken in with food or drink; and in many instances its ill effects are allowed to continue long, and are perhaps misinterpreted, because the source of impregnation is hidden. The practitioner should be careful to guard against mistakes of this kind, and, whenever symptoms analogous to those of lead-poisoning come under his observation, should diligently search for the cause in the occupations, habits, diet, and various exposures of the patient. The blue discoloration of the gums is an invaluable sign in such instances. It is not only those engaged in the processes in which lead is used who are liable to be affected, but also all who may be exposed, from residence or accidental vicinity, to the same influence. In relation to food, independently of the occasional presence of the preparations of lead from pure accident, carelessness, or malicious intention, the poisonous impregnation may proceed from the use of lead glazing for earthen-ware, or of soldering in metallic vessels, especially when acid substances are introduced into them, as in the instance of pickles or preserves. But drinks are much more liable to this impurity. Water, through the agency of the absorbed oxygen and carbonic acid, always contained in it when exposed to the air, is capable of acting on metallic lead, forming an oxide or carbonate, which may be held in solution in minute proportion. Of course the same result must happen from contact with the carbonate already formed. Hence, lead-poisoning has often proceeded from the use of water as drink, which had stood long in leaden reservoirs, or passed through leaden pipes; and the similar use of rain-water falling from a painted roof has produced the same effect. Certain natural waters, in consequence of the protective agency of the salts which they contain, are less liable to be thus rendered noxious than pure water. This is particularly true of those containing carbonates and sulphates. It has been supposed that these act by forming carbonate and sulphate of lead, which, being insoluble, are precipitated as rapidly as they are formed, and, giving a coating to the surface, prevent the contact of the water with the metal. This may be partially true; but such a coating must be an uncertain protection, and in fact has often proved insufficient. A better explanation of the effect of these salts is, I think, the following. The carbonates and sulphates referred to are usually those of lime. In the instance of carbonate of lime, which is in fact a bicarbonate, the proper carbonate being insoluble, one equivalent of the carbonic acid seizes the oxide of lead, as fast as formed, and the reproduced carbonate then appropriates the free carbonic acid in the water, which is thus rendered incapable of acting as a solvent to the carbonate of lead produced; for this carbonate is quite insoluble in pure water. A little carbonate of lime in the water may thus serve as a carrier of the carbonic acid from the water to the oxide of lead, and keep the liquid free from both. In the instance of the sulphate of lime, the sulphuric acid combines with the oxide of lead as rapidly as it is generated, or decomposes any carbonate of lead that may have been produced, in either case forming a totally insoluble sulphate of lead, while the liberated lime would neutralize any free carbonic acid in the water. It is thus seen that these salts preserve the purity of the water, not simply by forming a mechanical impediment to its contact with the lead, but by separating the impurity at the moment of its generation. It is in this way probably that the Schuylkill water, with which the city of Philadelphia is supplied, is kept free from lead, though constantly flowing through leaden pipes. Water containing chlorides is not similarly protected. I have known colica pictonum to prevail in a neighbourhood where the pump-water is brackish, simply from the introduction, as a substitute for the common pump, of an apparatus containing a small portion of leaden pipe.