Experimental studies on the inhalation of lead by human subjects

I have only a short time at my disposal in which to connect up certain experiments which are related to the subject of this Symposium, based on the work of many years in the Kettering Laboratory on the general problem of the biological significance of lead. In order to do this I must cover the ground hastily and only in outline, and I shall have to rely upon your willingness to go to the literature later for the evidence on which certain statements of fact are based. This work began in 1927-28 with an examination of the occurrence and distribution of lead in nature, especially in biological materials. This task has not been completed, but the general background has been established, and some of the facts are highly pertinent to our discussion here. The summarized results of the early work were published! in 1933, and other publications have followed since 24 • Some years later, we began a systematic investigation of the metabolism of lead in human subjects under normal conditions, and then under artificial conditions involving the oral administration of lead, daily, over long periods of time (in one instance, for 4·5 years), at several levels of dosage. The results of these investigations have been published briefly46 and, because of their elaborate nature, the experimental procedures and findings have not been described minutely in all of their physiological significance. A full account will be given in a monograph which will deal both with methods and data, as they bear on this participant in the mineral metabolism of the body, as well as on a variety of medical and hygienic problems. In 1950, we initiated the present phase of the work-one toward which the investigation of the fate of ingested lead had been moving-by entering upon a study of the behaviour of inhaled, particulate lead compounds in the human organism under carefully controlled conditions in the laboratory. These observations, as well as those concerned with the ingestion of lead by human subjects, could be carried out within physiological limits. Since members of the Laboratory staff had had experience in the field of industrial hygiene in the lead trades, there would be no risk of inducing even incipient manifestations of lead intoxication. Clinical and chemical (analytical) observations had been made systematically in a wide variety of such trades for many years and had established, beyond cavil, physiological criteria-levels