The theory of alternating current measurements in biology and its application to the investigation of the biophysical properties of the trout egg.

Alternating current measurements in biology are concerned with the resistance and capacitance of the cell membrane, and the resistance of the cell interior. No systematic electrical measurements have so far been made on the cell nucleus. Such expressions as resistance, capacitance and impedance are generally associated with wireless sets or wireless components. They have, however, a physico-chemical meaning. The resistance of the cell membrane is a measure of the ability of ions to pass through it, while the capacitance of the cell membrane gives an indication of its dielectric constant which in turn is an indication of chemical composition. The capacitance depends on the distribution of charge on, in, or round the membrane. Substitution or deformation of dipoles, or alteration of the forces controlling the relative positions of charged particles will make the capacitance vary. If the dielectric constant is known or guessed, measurement of the capacitance enables the thickness of the cell membrane to be computed. The equation for the capacitance of a parallel plate condenser summarizes these relationships: