Previous to the employment of the x-ray as a means of detection of calculi in the ureter, the error in diagnosis between stones in the kidney and ureter was great. The employment of the x-ray has been of the greatest value in the diagnosis. This method of diagnosis, however, contains a two-fold error: first, the impossibility of detecting pure uric acid calculi; and, second, the presence of questionable shadows in, or near by, the course of the ureter. It has been a common mistake to cut down on supposed ureteral calculi because of shadows present in x-ray plates, and to find no ureteral stone, the shadow being due to a faulty plate, calcified gland, sclerotic artery, phlebolith, calcified bodies in muscle or fascia, or accentuated calcification in the transverse processes of the vertebræ. It has been recognized that a simple x-ray picture is subject to these