The effect of diamond dust alone and mixed with quartz on the lungs of rats.

Diamond, the hardest of all minerals, was classed as an inert material, similar to anthracite and corundum, by Gardner (1938) on the basis of intravenous injection experiments in rabbits. By intraperitoneal injection into mice Bovet (1952) produced collagenous nodules in places where much diamond dust was accumulated. But it took six months to one year for such nodules to form as against a few weeks for quartz of similar size. Schiller (1955) injected diamond dust intraperitoneally into mice, alone and combined with silicic acid in the form of " aerosil ". The diamond dust produced only very slight fibrosis of the tissues, but laminated fibrous granulomata were formed after 60 days in the animals injected with silicic acid plus the diamond dust, on which Schiller supposed the silicic acid had been adsorbed. Pure coal dust injected intratracheally into the lungs of different animals produces no other pathological result than the formation of a very few reticulin fibres within focal accumulations of the dust (Belt and King, 1945). Small amounts of free silica dusts (quartz, tridymite) are partly or wholly eliminated from the lungs into the lymph nodes and therefore produce little or no fibrosis in the lungs, but when these small amounts of free silica dusts are combined with large quantities of coal dust they produce more fibrosis in the lungs than the apparent sum of the two of them taken separately (Ray, King, and Harrison, 1951; Attygalle, King, Harrison, and Nagelschmidt, 1956). The same result was obtained with graphite, and we have now repeated the experiment with diamond dust alone and admixed with small amounts of quartz.