Repeatability potency

The most active extracts were obtained8 from L. mesenteroides cultures containing sucrose extracts prepared from L. mesenteroides organisms repeatedly transferred through D-glucose broth were of low potency.48 Active extracts in dilutions of 1 2 or 1 4 produced dextran in 5% sucrose solutions after one to two hours at 23°, and at pH 5.6 with acetate buffer demonstrable amounts of dextran were produced after twenty days with 1/10,000 dilution of the extract. Optimal yields of dextran were less than 5% based on sucrose. Small concentrations of dextran were detected by means of precipitin titrations with pneumococcus antisera Types II or XX (see page 215). 

Of course, identifying the biological potency of more complex compounds is far more difficult than the process shown here, hut the principle is essentially the same a process of iteration, repeated testing by which one compound after another of the active compound is determined. 

If the biological effect of a chemical is related to its dose, there must be a measurable range between concentrations that produce no effect and those that produce the maximum effect. The observation of an effect, whether beneficial or harmful, is complicated by the fact that apparently homogeneous systems are, in fact, heterogeneous. Even an inbred species will exhibit marked differences among individuals in response to chemicals. An effect produced in one individual will not necessarily be repeated in another one. Therefore, any meaningful estimation of the toxic potency of a compound will involve statistical methods of evaluation. 

Consider an assay as preliminary if its computed potency is less than 80% or more than 125% of assumed potency adjust the assumed potency accordingly and repeat the assay. Overage should be taken into account when determining target assumed potency. 

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