1. A modification of the Waugh-Ruddick test for increased coagulability of the blood is described, which employs the use of recalcifled plasma in the place of whole blood.
2. Using this modification, studies were carried out on a series of patients undergoing operation. It was found that there was an increased coagulability of the blood present within 24 hours following operation, and that this condition lasted for a week or so. In all cases, the coagulability had returned to normal by the end of two weeks.
3. It is felt that the change is due to an increase in the circulating thromboplastin, presumably derived from damaged tissue in the operative area.
ACKNOWLEDGMENT I wish to make grateful acknowledgment to Dr. T. R. Waugh for his advice and assistance during the course of this work and in the preparation of the manuscript.