different gases, had been the subject of experiment for many years, and a marked difference was noticed between the phenomena of light at the two electric poles. Light radiating from the positive pole extends. entirely through a vacuum tube; while light radiating from the negative pole produces only a very weak and diffused illumination. But as soon as the vacuum is increased to a high degree, the phenomena become entirely different. The light of the positive pole decreases, while that of the negative pole pervades the vacuum more and more, being permanently propagated in straight lines.

The light emanating from the negative pole is called the "cathode-ray." Lenard and Hittorf found that such rays have the power of creating fluorescence, heat, etc., and that they can be deflected by a magnet. The vacuum-tube that is commonly used is generally called the Crookes tube, after Sir William Crookes, who described and slightly modified the tube. The credit for having originally devised it is due to Geissler, an ingenious mechanician of Bonn, Germany.

As soon as an electric current of high intensity goes through the conducting wires fused into the ends of the tube, the negative electrode, or cathode, becomes surrounded by a faint dark-blue light, while the positive electrode, the anode, sends a peach-colored light through the tube as far as the light of the cathode. As the air is gradually rarefied, the positive stream of light almost disappears, while the negative cathode light extends more and more, and finally fills the whole tube.

In December, 1895, Röntgen, while experimenting with these tubes by surrounding them with black pasteboard, impermeable by light, discovered an astonish

ing phenomenon. On a screen standing near the tube, and painted with a light color (barium platinocyanid), he noticed a light as soon as an electric current went through the tube. It became evident at once that there was a radiant power that, although not perceptible to the eye, permeated the pasteboard. This force, heretofore unknown, also showed a marked effect on the screen. Röntgen, after having found that the effect of these invisible rays upon the screen was constant, tried photographic experiments also. He then discovered that under the influence of these rays his hand, resting upon the cover of a wooden box, gave a sharp silhouette on a drying plate below, although the cover was not removed. He also found that paper, wood, and even thin discs of metal, were permeable by the rays, while thick discs of metal, bones, etc., produced silhouettes. This latter discovery, in particular, at once aroused the most wide-spread interest in regard to its uses in surgery, and up to the present date its full significance can hardly be appreciated. Röntgen modestly suggested naming the new rays "X-rays," until their nature should be discovered; but Professor Kölliker, of Würzburg, very properly proposed calling them "Röntgen rays," and the veteran scientist's recommendation will probably be followed by men of science and by the profession.

The proofs of the great usefulness of the rays in surgery are now so overwhelming that to discuss them would be carrying owls to Athens. Their value in internal medicine has not as yet been made so apparent; still, much has been contributed in this field, and there can be no doubt that, with the better interpretation of the shadows and the continuous improvement of diagnostic technic, the significance of the rays in in many of

the obscurer ailments will be convincing to the mind. of the most skeptical.

The greatest usefulness of the rays thus far displayed is, however, in the recognition of fractures. Accuracy takes the place of ignorance and doubt, and painful manipulations cease to be necessary for diagnostic purposes. Even the most skilful experts in fractures are unable to deny that there is a large number of bone-injuries the character of which formerly could not be recognized, whether on account of the swelling of the area involved or from the obscurity of the symptoms. The number of cases of fracture formerly mistaken for contusion or distortion was enormous. It is in such cases that a simple glance with the fluoroscope furnishes the most precise evidence. Whether there is comminution or impaction or the intervention of muscular tissue or intra-articular fracture or combination with a dislocation, can be at once clearly determined. If the picture be fixed on a photographic plate, the nature of the injury can be studied at leisure, and the proper line of treatment easily decided upon without subjecting the patient to any tentative manipulations. After a dressing is applied, the skiagram verifies the proper position of the fragments. In fact, the proper execution of all therapeutic points can be verified throughout the course of treatment by the skiagram, the dressing itself, even if consisting of plasterof-Paris, being no obstacle to the rays.

Even the shoemaker can profit by the rays, which will prove whether shoes fit accurately-an item of great importance in the after-treatment of fractures or in club-foot.

If the therapy proves to be imperfect, the rays show the nature of the condition. It is easily determined,

for instance, whether an ankylosis be fibrous or osseous; and, consequently, the question whether the breaking-up of adhesions or resection is indicated is settled at once.

It is needless to call attention to the frequent importance of a skiagraphic proof in court, for the tection of the surgeon as well as of the patient.

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The greatest benefit obtained from the rays, in the proper judgment of the various types of fractures, is in connection with those situated in the neighborhood of joints. The special uses of the rays in diagnosticating the various types of fracture may be grouped as follows:

Fractures of the clavicle are, in general, easily recognized without the rays. Still, there are rare cases of infraction and fissure in which no deformity or crepitus is observable, and which could not be recognized except by the aid of the rays.

In fractures of the scapula the conditions are often so obscure that without skiagraphy the true nature of the injury may be veiled; for instance, when dislocation of the humerus is combined with fracture of the acromion.

In fractures of the humerus it is the shoulder-joint and elbow-joint that require the use of the rays most frequently. Especially in reference to the elbow-joint, it may be safely asserted that an exact diagnosis without skiagraphy is simply impossible in by far the great majority of cases. Skiagraphy will infallibly demonstrate the various types of elbow-fractures; it will, furthermore, show whether the line of fracture is transverse or T-shaped, and whether there are any complications, such, for instance, as a fracture of the olecranon combined with dislocation of the radius.

In fractures of the forearm it is the elbow-joint and the wrist-joint that especially require the use of these rays. In these cases as well as in those previously noted a large number of new facts have been revealed, which have entirely revolutionized our pathologic and therapeutic views.

Fractures of the bones of the hand occur much more frequently than was formerly supposed. Fractures of the individual carpal and metacarpal bones, and even of the phalanges, were often mistaken for contusions.

Fractures of the pelvis, the accurate recognition of which formerly offered the greatest difficulties, can also be readily demonstrated-the differentiation between contusion, fracture of the acetabulum or of the neck of the femur, and dislocation especially coming into question. Most valuable information can also be obtained as to the presence of impaction.

In fracture of the femur it is not only the hip-joint that may require the use of the rays, but also the shaft and the lower end of the bone. In the neighborhood of the knee-joint rapid swelling often absolutely prevents an accurate diagnosis except when the rays are employed. Furthermore, in all the different intraarticular complications the occurrence of epiphyseal separation, and the question as to the transverse or oblique or T-shaped line of fracture can easily be settled.

Fracture of the patella can easily be recognized without the aid of the rays. Still, there are some important questions-for instance, as to whether the fracture. is complete or incomplete, or whether there are several fracture-lines-that could not be determined without the aid of the rays. It goes without saying that in the proper determination of the after-treatment, in the cor