ABSTRACT
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.
d.c. pulses are considered as a special case of a.c.
If 1/ωCs is written as Xs (the reactance), Zs = Rs+ Xs/j or Rs–jXs. This expression will be used later.
rj= Rj/k. Therefore Rj/k is substituted for rj in each case. Equation (21·2) must be multiplied by a factor to correct for c3 being of the ‘polarization ‘type. This is discussed in detail later.
The standard arm could equally well contain a resistance and a condenser in series. The advantage of the parallel arrangement is that with it, one terminal of the resistance and of the condenser can be at earth potential, thus eliminating hand capacitances, etc.
If the network contains more than one condenser, this analysis is incorrect.
In a capacitative circuit where E=E0 sin ωt, the charge Q on the condenser is CE=CE0 sin ωt. I=dQ/dt; therefore 
. The current leads the voltage by 90°.
This is only true when the Rs–jXs plot is a semicircle. The more general case, when the plot is an arc of a circle, as in Fig. 7, is discussed below.
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