Because the internal fields cannot be quantified, the actual "dose" of electric field received by
test subjects in electric-field studies is not well defined. This poses no problem with regard to the
characterization of the dependent parameter in any particular experiment, because it is always possible
to specify the strength of the applied electric field-the field that exists before the presence of the
subject. Moreover, the applied field is an appropriate measure by which to compare different
experiments on the same species. There is a problem, however, in relating electric-field studies that
involve different species. Because of shape and structural differences, the amount that various animals
perturb the applied electric field, and the dose they receive from it, vary greatly-a factor of 5-10 would
not be surprising. Thus, for example, a particular biological effect observed in rats following exposure
to I kv/m would not necessarily be expected to occur in monkeys at that field strength.
Techniques of Application of Electromagnetic Fields
Electric field. A typical laboratory arrangement for the application of an electric field to a test
subject is depicted in figure 4.4. If the linear dimensions of the plates exceed the distance between them
by greater than a factor of 2-3, then the electric field, measured in volts (v) or kilovolts (kv) per meter
(m), is relatively homogeneous and, at least in the absence of the test subject, it is given by V/d.
Reliable methods for measuring the electric field have recently been developed (61). An exposure
assembly that is suitable for use with small animals at low frequencies is shown in figure 4.5.
Fig. 4.4. Arrangement for application of electric fields.
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