A more practical method is to ensure that in all cases radiograms of any part of the body be absolutely comparable with one another by taking care to maintain the same relationship between the X-ray tube and the part under examination. For example, in making an examination of the ankle-joint, the limb is placed in a prescribed position, and the anode of the X-ray tube, that is, the actual source of the X-ray, is brought into accurate relationship to the tip of the internal malleolus by a simple mechanical contrivance, the details of which need not be dealt with here. This relationship between the tube and the ankle can always be reproduced, and therefore the shadow of a normal ankle-joint can always be obtained under the same conditions for comparison with the radiogram of the suspected ankle. In this way, not only is the surgeon able to select the view of the part which will have the depth and detail necessary for proper interpretation, but, the shadow being familiar, he can more easily recognize any abnormality. A radiogram secured under the conditions usually adopted, shows definite and known anatomic relationship between the bones and the X-ray tube, namely, with the anode of the tube directly opposite the tip of the internal malleolus. To render this method of examination more perfect, there has been devised a system of radiography containing a definition of the relationships between the tube and the various parts of the body which have been found to give the most useful views, and also radiograms of the normal appearances of each part at the ages respectively of 5, 15, and 25 years. By using this system the surgeon can secure a radiogram of any part of the body, of the requisite standard in quality, while he has at hand a normal radiogram of that part for comparison with the abnormal. Having secured a radiogram of good quality, it is necessary for the purpose of interpretation that it should be viewed in a suitable light. The best for the purpose is a bright light shaded with opal in a dark room. The negative may be viewed at its best while still wet. Considerable loss of detail follows the taking of prints, which for this reason may greatly detract from the value of the radiogram. It is a mistake to suppose that X-ray examination in the diagnosis of diseases can replace the older and well-tried clinical methods of investigation; it is merely a useful means of acquiring knowledge which, in conjunction with accurate clinical investigation, leads to a more accurate diagnosis and prognosis, and is often most useful by suggesting a more suitable line of treatment. It must be remembered that this method of investigation has been in use only a comparatively short time. In some diseases no definite statement is yet possible that may not prove in the future to be misleading.