Letter from Howard Walter Florey to Robert Cook, Dundee Cook's work may be important if he finds a cheap strain producing high yields of penicillin - must be careful with assays - has heard of super media which, on closer examination, were no good - if Cook has difficulty, he should write to [N G] Heatley - is sending dry sample of an American strain - will be interested in Cook's results. On verso is a letter from Cook to Florey, 26 November 1943: thanks for sample - getting high yields from Fleming's original strain (penicillium notatum) - would like to tryout some high yielding American strains in their medium - medium costs 1d-2d a litre. 1 December 1943