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The development of birefringence as a function of the ionic concentration of DNP structures has been studied in HeLa and monkey kidney cell cultures. The cell nuclei were isolated on coverslips with 0.1% NP40 or Triton X100 dissolved in isotonic sucrose and NaCl of different molarities. Below 0.07 M NaCl concentration the nuclei were isotropic. Between 0.08 and 0.11 M only the perinucleolar chromatin showed birefringence, whereas at higher cationic concentrations the entire nucleus, including the heterochromatic structures became anisotropic. It is assumed that the differing dissociation constants of the various DNP structures might be responsible for the development of this ion-dependent polarisation optical effect.

Summary The mobility of silicogenic dust samples (cristobalite, erosil, tridymite, silicon dioxide and vitrinite) was studied by microelectrophoresis, which showed that they differed in surface potential. A relationship was found between surface potential and severity of tissue damage.

In HeLa cells cultured in a medium containing 142 mequiv./l. sodium ions only the mitotic forms are birefringent (anisotropic index, 27/1000). In a culture medium containing 155-160 mequiv./l. sodium ions, large numbers of nuclear forms reminiscent of the prophase were found. In such a medium the anisotropic index was 86/1000. At low sodium ion concentration (90-110 mequiv./l.) these anomalous, prophase-like forms were not seen and the anisotropic index was 18/1000. The appearance of the birefringent, prophase-like forms is related to a structural rearrangement and condensation of DNP in a hypertonic medium.