Clinical similarities between shock and the effects of hemorrhage are so numerous that some authorities have regarded the two as identical. It is believed by many that hemorrhage will produce the complete syndrome of shock—a belief which we formerly supported.1 We supposed that anoxia in the tissues resulting from the effects of hemorrhage would cause endothelial permeability, hemoconcentration and other features characteristic of shock. Blalock2 had reported such results, and these coincide with our belief as published; but attempts to substantiate that belief experimentally produced results which were not anticipated. We made the simple experiment of withdrawing measured amounts of blood from the femoral veins of an unanesthetized dog (no. 338) weighing 10 Kg., allowing intervals of time for physiologic readjustment of the circulation. Erythrocyte counts and hemoglobin determinations were made (by the photoelectric method) before and at intervals during the experiment. Examinations of the blood, including one