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Swelling of nuclei in Amoeba proteus is quite independent of the ionic strength of the medium or the osmolarity. Rather, it seems that surface charge is important in determining the configuration of a biological membrane which could give rise to large and specific changes in its permeability.

Naegleria gruberi is a small (∼15µ diameter) free living cell which is able to transform reversibly from the amoeboid to the flagellate state1. The amoebae move by forming one or more lobose pseudopodia, any one of which may be considered to define a functional anterior end. It was observed, quite unexpectedly, in the course of electrophoretic characterization of the cell surface, that individual freely suspended amoebae manifest a transient local difference in mobility during pseudopodal protrusions, the anterior pseudopodal end having a higher negative mobility. While this suggests that the advancing pseudopod possesses a higher negative zeta potential, and thus higher negative surface charge density than the rest of the cell, it is open to alternative interpretations.