There can be no doubt of the great utility of the X-rays in the diagnosis of various morbid conditions, although this mode of investigation, like other physical methods of exploration, may in some instances be not infallible, and in others it may alone be insufficient to yield the desired information. The X-rays are capable of disclosing differences in density of structure, and where these are sufficient to be appreciable as shadows to the eye of the observer, there the rays will be of service. It must be borne in mind, however, that wide variations exist in visual acuity, and, in particular, in that special kind demanded in X-ray work, and, further, that this may be sharpened by constant exercise. The X-rays can not disclose the actual nature of the structures responsible for the variations in density that give rise to fluoroscope or skiagraphic shadows. This information must be supplied by