Observations on the pathogenesis of silicosis by means of the diffusion chamber technique.

An attempt has been made to determine whether the diffusion chamber technique can be used to decide the validity of the silica solubility theory of the pathogenesis of silicosis. Small chambers were constructed from membranes of a pore size which allowed free passage of colloidal silicic acid and tissue fluids but which prevented the entry of host cells and the exit of the larger silica particles. Significant fibrosis failed to develop around chambers containing five different forms of silicon dioxide when inserted subcutaneously and intraperitoneally in rats and rabbits. All five forms of silica were actively fibrogenic when brought into direct contact with peritoneal tissues. However, in vitro experiments suggest that colloidal silicic acid, the form which may be involved in silicotic fibrosis, does not escape from the chambers. Thus the biological results obtained by this technique do not necessarily invalidate the silica solubility theory of the pathogenesis of silicosis.