ABSTRACT
The spontaneous rhythmical impedance changes that occur in fertilized and unfertilized eggs of the rainbow trout after about 7 hr. immersion in tap water have been analysed. They are found to be almost entirely capacitative and correspond to a change of between 5 and 10 % when measured at a frequency of about 1.0 kc. The possibility of any associated resistance change being virtually unobservable is discussed.
These changes, which have not so far been recorded in other living material, are compared with the impedance changes that occur in nerve cells and Nitella.
Cole (1941) interprets the electrical behaviour of nerve membranes as being due to inductance as well.
This can be explained briefly as follows. The oscilloscope measures the potential across the bridge. At balance this potential is zero; at off balance the potential oscillates around zero, because the source is alternating. Therefore in every cycle the potential is positive (‘above ‘zero), and negative (‘below ‘zero).
It also involves the assumption that Maxwell’s equation, referred to earlier on, is applicable. This is not the case because of the shape of the electrodes and their proximity to the egg, but the equation can be used to get a rough idea of the order of magnitude of the change.
Prof. K. S. Cole has drawn my attention to the fact that if the membrane impedance can be expressed in the form Z3= K ω− α, where if is a constant, and log Z3/K. is plotted against log <u, there is a discrepancy between the slope of this line (− α) and the phase angle across the capacitance of the membrane as measured in the circle diagram 
. This discrepancy, which only occurs significantly in the first of the circle diagrams in Fig. 5, may be due to trout eggs not always obeying the empirical Z3= K ω− α rule; on the other hand, this particular batch of eggs had unusually variable phase angles. Whether this was due to an inherent variability in the eggs or to an extraneous factor is not known.
