T h e physiological or biological effect to be observed in the screening is
critical. One of the simplest biological responses is to monitor the lethality, since
there is only one criterion; either dead or alive. In that case, the statistical analysis
is relatively easy. The lethal concentration for 50% mortality after 24 h of
exposure (the chronic LC50) is determined as the measure of toxicity of the extract
or compound. The choice of time, governed by the solubility of the extract or
substance, is largely one of convenience, since the test is to be rapid and kept
simple [3-6]