[14] OLIVER, SIR T.: Lead Poisoning (Goulstonian lectures). 1891. [15] SCHICKSAL: Die Bekämpfung der Bleigefahr in der Industrie, p. 38. 1908. [16] STEINBERG: International Congress of Industrial Hygiene. Brussels, 1910. [17] CLOETTA: Dixon Mann’s Forensic Medicine and Toxicology, p. 463. [18] LITTLE: The Lancet, March 3, 1906. [19] CANUET, T.: Thèse, Paris, 1825, No. 202. Essai sur le Plomb. [20] DROUET: Thèse, Paris, 1875. Recherches Experimentales sur le Rôle de l’Absorption Cutanée dans la Paralysie Saturnine. [21] MANOUVRIER, A.: Thèse, Paris, 1873, No. 471. Intoxication par Absorption Cutanée. CHAPTER III 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.