Conductivity measurements of ${\mathrm{PbCl}}_{2}$ and ${\mathrm{PbBr}}_{2}$ under pressure have been carried out by Oberschmidt and Lazarus. The migration and activation volumes scale with the corresponding enthalpies in a manner predetermined by the bulk properties. By considering the existing data for a large variety of solids (rare-gas solids, lithium halides, lead halides, ${\mathrm{SrF}}_{2}$, and olivine) in which the defect enthalpies vary by two orders of magnitude we conclude that there is a curve which connects in a unified manner the point-defect data with the bulk properties.