The location of the pain in his early history and the X-ray report certainly indicated the left kidney as the more probable one to be affected. Therefore, on March 13, 1909, a nephrotomy of the left kidney was done. The kidney was low and lay almost transversely. The pelvis and ureter were entirely uninflamed but much dilated, the ureter being larger than a lead pencil. An incision into the ureter allowed about 100 cc. of apparently clean urine to escape. A soft rubber catheter was introduced into the ureter and stitched into the lumbar wound. Now comes the startling feature of the whole story. Immediately after the operation, _all urine stopped coming from the urethra and perineal wound_ and in its stead came only pus, while apparently normal urine flowed from the tube in the loin. This continuing to be the case, forced the conclusion that the right kidney was either absent or practically destroyed; the latter view was substantiated by an excellent X-ray, subsequently made, showing a small atrophied kidney on the right side. The patient made an uninterrupted recovery from his kidney operation, but his perineal fistula never completely healed. Three years after his nephrotomy he was re-operated upon in order to close his perineal fistula and died as a result of shock. In the meantime, however, he had gained much in weight, had improved generally and returned to his work. No T. B. bacilli could be found in his urine at the time of his last operation. Here, then, is an instance in which the X-ray, which had rendered so valuable a service in the preceding case, deceived the surgeon and then later redeemed itself, to some extent, by demonstrating the size of the right kidney. For the radiograph of the left kidney showed a rather typical picture of pyonephrosis. Hence, obviously, the lesson to be learned from this is that under certain conditions, water may throw a shadow similar to that of pus, so that it is not always possible to differentiate a pyonephrosis from a hydronephrosis by such means. The crater-like appearance of the right ureteral orifice, though quite suggestive, was hardly evidence enough to warrant a diagnosis of tuberculosis of the right kidney, but had it been possible to catheterize both ureters or even only one (either one), the question of the involved kidney, the approximate amount of involvement, and the condition of the opposite kidney, could have been readily cleared up.