Letter from Howard Walter Florey to H G Bensted, War Office, Grosvenor Place Is sending sodium penicillin of 40 units per mgm - it is very hygroscopic - advisable to refrigerate for journey - users should test to see if it is still active - suitable for local use only - gives details of application - might like to try it on infected fingers - penicillin is not antiseptic, only a bacteriostatic. 15 July 1942