If the chest is examined by the Röntgen rays the lungs are seen as light spaces between the clearly marked ribs, and any spot of congestion appears as a darker patch. In this way the early stages of consumption may be revealed, and in pneumonia and other similar complaints valuable information regarding the condition of the lungs can be obtained. It is possible also to follow to a considerable extent the processes of digestion. X-rays easily pass through ordinary food, but if bismuth oxychloride, which is quite harmless, is mixed with the food, the mixture becomes opaque to the rays, and so its course may be followed on the screen. The normal movements of the food are well known, and an abnormal halt is probably caused by an obstruction of some kind, and thus the X-rays enable the physician to locate the obstruction, and to form an opinion of its nature. In our chapter on wireless telegraphy we saw that the discharge of a Leyden jar takes the form of a number of rapid oscillations backwards and forwards. These oscillations take place at a rate of more than half a million per second, but by the use of an apparatus called a “high frequency transformer” the rate is increased to more than a million per second. Electricity in this state of rapid oscillation is known as high frequency electricity, and high frequency currents are very valuable for some kinds of medical work. The application of these currents is quite painless, and but for the strange-looking apparatus the patient probably would not know that anything unusual was taking place. To some extent the effect maybe said to be not unlike that of a powerful tonic. Insomnia and other troubles due to disordered nerves are quickly relieved, and even such obstinate complaints as neuritis and crippling rheumatism have been cured. The treatment is also of great value in certain forms of heart trouble. By increasing the strength of the high frequency currents the tissues actually may be destroyed, and this power is utilized for exterminating malignant growths, such as lupus or cancer. The heat produced by a current of electricity is made use of in cauterizing. The burner is a loop of platinum wire, shaped according to the purpose for which it is intended, and it is used at a dull red heat. Very tiny electric incandescent lamps, fitted in long holders of special shape, are largely used for examining the throat and the various cavities of the body.