In previous studies, 1 the composition of the blood with particular reference to the protein content has been determined in experiments in which a decline in blood pressure produced by a variety of means was accompanied by the introduction of fluids. The fluids were injected intravenously in most of the experiments, and they included those frequently used in treating shock. In one group of studies,1b an unexplained decline in blood pressure occurred. This drop appeared either before or shortly following the beginning of the introduction of fluid intravenously into normal anesthetized dogs. Usually the arterial pressure remained depressed for only a short time and then returned to the previous control level. The decline in blood pressure occurred in a few of the experiments in which solutions of salt or of dextrose were used, and in most of those in which an unpurified solution of acacia was injected. In all