Letter from Howard Walter Florey to J W Trevan, Wellcome Physiological Laboratories, Beckenham Compares the effects of intramuscular injection of calcium and sodium salts - also of Trevan's material and that from ICI - calcium salt desirable for local use, sodium salt for parentereal injection - describes extraction with barim hydroxide from chloroform - not clear why Glaxo uses sodium bicarbonate for making final sodium extract - has received some penicillin from Merck's - gives details - standards have improved. 12 May 1943