1. The theory of alternating current measurements as applied to biological systems is discussed and the equations for determining the resistance and capacitance of the cell membrane, and the resistance of the cell interior are deduced.

2. Maxwell's equation for the specific resistance of a random suspension of spherically packed homogeneous spheres is involved in these equations, and its applicability to single glass spheres of various diameters is established.

3. This method of analysis is applied to the egg of the trout, to examine the capacitance of its cell membrane before and after fertilization. If the membrane resistance is assumed to be infinite, the capacitance of the cell membrane, scaled to a standard frequency of 1 kcyc., is approximately 0.57µF.cm.-2 in unfertilized eggs and 0.58µF.cm.-2 in fertilized eggs. The difference is not statistically significant.

4. The capacitative element of the cell membrane has a constant phase angle of about 83° in fertilized and unfertilized eggs, indicating dielectric loss in the membrane.

5. The characteristic frequency of fertilized and unfertilized eggs was between 0.8 and 0.9 kcyc.

6. The internal resistance of the egg varied in different batches but in general was higher than that found by Gray (90 ohm-cm.). The average value for 32 eggs was 206 ohm-cm.

7. The experiments described in this paper are neither connected with, nor affected by, the periodic impedance changes which occur at a somewhat later stage in fertilized and unfertilized trout eggs.

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