Summary: The general form of assay for streptomycin described by Brownlee, Delves, Dorman, Green, Grenfell, Johnson & Smith (1948), based on an 8 × 8 quasi-Latin square layout of cavities on a large agar-covered glass plate, in place of Petri dishes, can be adapted to penicillin. A new design, using the principle of double confounding, allows the estimation by the usual four-point assay, of seven (instead of three) unknown solutions per plate of 64 holes. In routine use this assay gives fiducial limits (P = 0·95) of about ± 9·6%, including dilution errors.

The assay procedure previously described in this Journal (Brownlee . 1948) for streptomycin, is immediately adaptable to penicillin. For dealing with large numbers of fermenter samples in particular, we have found modifications desirable, which we describe in the present paper.


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