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The loss of absorption of the chromophoric group of thymine on irradiation in aqueous solution withy-rays has been studied under a variety of conditions. The effects of thymine and oxygen concentrations, of pH and of the presence of N20 have been investigated. In solutions containing oxygen, the loss of absorption is the result of initial OH radical attack on the pyrimidine molecule ; radiation-induced electron attachment to thymine does not lead to destruction of the chromophoric group if oxygen is present in the system. Aerated thymine solutions (8 x 10-5-2 x M) have been used to determine, spectrophotometrically, the relative reactivities of solutes towards OH radicals ; because of an unusual pH effect observed in neutral solutions, the competition experiments were carried out below pH 6. The reactivities of a number of organic solutes have been obtained. Similar rate constant ratios were obtained in solutions containing NzO, indicating that NzO-was not an oxidizing species under the conditions of the experiments.

. Prostaglandins E1 and E2 contracted the longitudinal muscle of human, guinea‐pig and rat isolated ileum. . The site of action varied with the species. In the rat and in some strips of human tissue prostaglandin appeared to have only a direct action on or in the muscle cells. In the other strips of human tissue and in guinea‐pig ileum the prostaglandins seemed to stimulate both the intrinsic cholinergic nerves and the muscle cells. . In contrast to the longitudinal muscle, the circular muscle of human, guinea‐pig and rat isolated ileum was usually inhibited by prostaglandin, apparently by an action directly on the muscle cells. . Prostaglandins may play a part in the control of intestinal motility.

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