English: Woman having a fluoroscopy of the spine in 1909, using the earliest type of x-ray apparatus. The early Crookes x-ray tube supported by the pole is covered with a lead shield so it only emits a beam toward the patient. It is powered by high voltage electricity generated by the large electrostatic machine in the background, probably a Holtz machine. The doctor holds a fluorescent screen up to her back, a piece of glass painted with a fluorescent chemical such as calcium tungstate or barium platinocyanide, and the x-rays passing through her body cause areas where they strike to fluoresce with a greenish glow. No precautions against radiation exposure are taken, as its dangers were not known at the time.