In many persons who have worked in lead for long periods, wasting does not progress beyond a certain point, and these persons may be regarded as having established a certain degree of immunity. Men are met with who have worked in white lead factories and in smelting works for periods of from twenty to, in one case, forty-three years, a considerable portion of such period being antecedent to the time at which the regulations in force for dust removal and general protection of the workers were established, and they must have been exposed to much lead dust. Nevertheless they were less emaciated than many who have only worked a year or two years in a factory under modern hygienic conditions and special regulations. Such persons are either immune from the commencement, or they have established a certain degree of tolerance towards the metal; the latter supposition is the more probable, as there is reason to think several of them suffered from a mild degree of poisoning during the earlier years of their employment. The rate of development of pallor and wasting are the important facts in incipient poisoning. Anæmia, together with the presence of basophile granules in the red cells, in a previously healthy person, and diminution in the hæmoglobin to 75 per cent., is definite evidence that absorption is leading on to poisoning--that is, blood-destruction--and coincidently insidious damage to the finer bloodvessels and their nerve-supply (see Chapter V.). Such a person may at any moment develop a sudden attack of colic or paresis.