The several parts required for the production of these rays are—1, a static machine, or a supply from the street mains; an induction-coil; 2, a vacuum-tube in which the rays are excited; 3, the fluorescent screen, or fluoroscope; and 4, the photographic plate, on which the image of the part is taken.

The static machine employed for this purpose is usually of the Holtz form, or some modification of this instrument. There must be a sufficient number and size of the revolving plates to furnish a spark of proper volume.

The current may also be obtained from a coil charged by the street mains, or by a dynamo, or by a storage or gravity battery.

The most important part of the apparatus for producing the X-rays is the vacuum-tube, originally a Crookes tube. This is a glass bulb 10 centimetres in diameter, with metal terminals—cathode, anode, and the anticathode or target. The cathode and anode are made of aluminum, and the target for the reception of the cathode stream is composed of platinum alloyed with iridium. In the single focus-tube the anode and target are combined, and is then made of the alloy of platinum and iridium.

Next in importance to the vacuum-tube is the fluorescent screen for the separation of the X-rays. This is a piece of cardboard coated uniformly on one side with tungstate of calcium or platino-chloride of barium. The size of the screen varies with the size and position of the part to be examined.

The photographic plate for receiving an impression of the part under examination is the final part of an equipment for X-ray work.

The use of the X-ray for diagnostic and therapeutic purposes has become an indispensable adjunct in surgical and medical practice.