Jet action from experimental “berry” aneurysms was evaluated as part of a long-range study of stress-strain-time relations of aneurysmal rupture. It was apparent that free jet action was a potent stress agent upon matter in its path. Calculated velocities of free jets ranged up to 477 cm. per sec. Supplementary observations were made upon jets from glass-model aneurysms, including the jet effects upon gelatin blocks cast about the models. Coefficients of velocity were determined for the various jets studied and the results were correlated with theoretic hydraulics.