In a previous study by one of us (Dr. Blalock1) the effects of graded hemorrhages on the cardiac output and blood pressure were determined. In experiments on dogs anesthetized with morphine it was found that the repeated removal of blood is usually associated with a decline in the cardiac output from 30 to 50 per cent below the normal level before a marked diminution in the mean blood pressure occurs. In subsequent experiments2it was found that the loss of blood into the injured area after trauma to an extremity was instituted was sufficient to account for the decline in the blood pressure. Mild trauma to an extremity,3trauma to the intestines3and burns3were studied, and the results indicated that the loss of plasma into the injured area was the chief if not the sole cause of the sustained low blood pressure that resulted.