Letter from Howard Walter Florey to Henry Dale, Royal Institution Has been unable to extract any activity from Costa Rican Puff Ball - might be active in fresh state - comments on work being done in collaboration with Dr Wilkins on British fungi, some of which produce antibiotics - wonders if puff balls could be examined on the spott - only one of plants described in medieval herbals for wound treatment is antibacterial - substance is toxic when purified. 12 July 1944