Letter from Howard Walter Florey to A Lang Brown, Hemel Hempstead Impossible to have assays of penicillin done in department - procedure highly organised and assays accurately done by Standards Department at Mill Hill - sure that this is where Brown should get material assayed - says Harington would cooperate if Brown wanted matter kept quiet - does not know how Brown is to get hold of samples - will be in London on 11th and 12th. 4 December 1951