" DAMMED CIRCULATION" " AND " INTERRUPTED CIRCULATION."
560 good apparatus it will be found that the test shadows can easily be obtained in ordinary cases. In the same way the method can be used to test the effects on the photographic plate. This is of special value when, owing to the stoutness of the patient, the shadows cannot be shown on the screen. The plate is much more sensitive than the human eye to x ray impressions and under certain conditions its results are more accurate. A radiogram is taken with the test placed between the tube and the
... n the tube and the patient in the same manner as in the screen examination. If the test shadows show on the plate another radiogram taken under exactly the same conditions, but without the test, will show ' , any calculus in the patient. The tube, however, varies considerably during even one ordinary exposure and a quite accurate result can only be obtained by taking a radiogram to include both sides of the patient and with the test on the side opposite to that under examination. This is especially useful in renal cases. When an image of the test is shown through one kidney it can be used as before to compare any opacities in the other. renal area or to prove that if there is no opacity there is no stone. A convenient plan, when the test shadows cannot be seen with the calculi between the tube and the patient, is to place the test immediately under the screen. The rays now pass first through the patient and then the calculi and therefore an image of the test will not prove that a calculus in the patient must also be seen. But if the rays can show the test they will be found sufficient to give a definite image of any calculus in the patient on a radiogram. In a comparatively small number of cases, those of very stout patients, it will be found impossible to show the test calculi by any method. In these the x rays are valueless and the diagnosis must be made from the physical signs and clinical symptoms. But it is of great practical importance to differentiate these patients from the large number in which it can. be proved that no stone is present and thus to decide whether or no an exploratory operation is justifiable. A negative result with the ordinary radiographic methods may mean either that no stone is present or that the rays have failed to show it, and unless the value of the rays employed is known the diagnosis is of no practical use. Even in a simple case a good photograph showing all the socalled typical diagnostic signs may, and sometimes does, fail to show a stone and, from its very photographic excellence, be worse than useless as a radiogram. The method gives the best results by the combined use of the screen and plate. On the former the presence and position of any opacity, its size, and relative density are noted, and especially when there is any movement on respiration, whether it is synchronous with that of the kidney shadow or of the intestines. The information obtained in this way can then be verified by a radiogram and in doubtful cases by re-examining any suspicious areas. Calculi placed outside the body have previously been demonstrated and a useful modification of the method described has been employed in searching for foreign bodies in the oesophagus, stomach, &c. In cases of urinary calculi it is in the systematic use of the method that its value lies, and in providing a standard of comparison and a practical means of estimating the actual diagnostic value of the x ray results.