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.