Effect of aluminium on the silicosis-producing action of inhaled quartz.

The claim of Denny and others (1937; 1939) to have prevented silicosis in quartz-dusted animals by the simultaneous administration of aluminium was not substantiated in the experiments of Belt and King (1943) and of King and others (1945), using the intratracheal injection technique of Kettle and Hilton (1932). But it was pointed out by King (1947), in similar experiments, that the aluminium might disappear from the lungs of animals which had received a single dose of mixed quartz and aluminium by the intratracheal route, leaving the quartz behind to exert its fibrogenic action after all the aluminium had been dissolved. It may be, therefore, that aluminium can exert its preventive or retardative action on silicosis production only if it is constantly renewed in small amounts in the lungs. The only type of experiment where this can be easily accomplished is one in which both the quartz and the aluminium are administered by daily inhalation. During the last ten years several attempts have been made ir this laboratory to produce silicosis in rats, guinea-pigs, and rabbits by the tumble-mill dusting technique of Denny and others, and to prevent silicosis by dusting similar animals simultaneously, or alternately, with quartz dust from a rubber-lined mill and aluminium from a mill of aluminium containing shot and slugs of the metal. These experiments have been unsuccessful. In the present experiment a new kind of cabinet and a new method of producing dust clouds have been used (Wright, 1948); and success has finally been obtained in preventing, or at any rate retarding, the production of silicosis in the lungs of a majority of rats given aluminium and quartz to breathe, as compared with marked and rapidly developing silicosis in the lungs of control rats breathing quartz dust without the admixed aluminium.