Copy letter from John Henry Gaddum, Department of Pharmacology, University New Buildings, Teviot Place, Edinburgh, to Dr [Maurice] Rapport Thanking Rapport for a sample of serotonin which he had in America. Gives an account of its use, including on a guinea-pig's intestine. Gaddum was surprised to find that serotonin was a depressor of a rat's blood pressure. Asks if his corrrespondent has made any progress with the pharmacology or chemistry of these substances and whether it has been proven to be 5-hydroxytryptamine. Queries if the Upjohn company have synthesized it. 24 August 1951