CELSUS noted more than nine hundred years ago that "fluid often collects within the abdomen so that if it be shaken by any movement of the body the fluctuations of the fluid can be seen."1 Since that time the recorded physical signs of relatively small amounts of free fluid in the abdomen have been generally unsatisfactory.2 In the course of two years of study, we found a very reliable physical sign, the puddle sign, which is present consistently with as little as 120 ml. of peritoneal fluid and which is not influenced by marked obesity or the presence of considerable . . .