<P> On November 8, 1895, German physics professor Wilhelm Röntgen stumbled on X-rays while experimenting with Lenard and Crookes tubes and began studying them . He wrote an initial report "On a new kind of ray: A preliminary communication" and on December 28, 1895 submitted it to Würzburg's Physical - Medical Society journal . This was the first paper written on X-rays . Röntgen referred to the radiation as "X", to indicate that it was an unknown type of radiation . The name stuck, although (over Röntgen's great objections) many of his colleagues suggested calling them Röntgen rays . They are still referred to as such in many languages, including German, Danish, Polish, Swedish, Finnish, Estonian, Russian, Japanese, Dutch, and Norwegian . Röntgen received the first Nobel Prize in Physics for his discovery . </P> <P> There are conflicting accounts of his discovery because Röntgen had his lab notes burned after his death, but this is a likely reconstruction by his biographers: Röntgen was investigating cathode rays from a Crookes tube which he had wrapped in black cardboard so that the visible light from the tube would not interfere, using a fluorescent screen painted with barium platinocyanide . He noticed a faint green glow from the screen, about 1 meter away . Röntgen realized some invisible rays coming from the tube were passing through the cardboard to make the screen glow . He found they could also pass through books and papers on his desk . Röntgen threw himself into investigating these unknown rays systematically . Two months after his initial discovery, he published his paper . </P> <P> Röntgen discovered their medical use when he made a picture of his wife's hand on a photographic plate formed due to X-rays . The photograph of his wife's hand was the first photograph of a human body part using X-rays . When she saw the picture, she said "I have seen my death ." </P> <P> In 1895, Thomas Edison investigated materials' ability to fluoresce when exposed to X-rays, and found that calcium tungstate was the most effective substance . Around March 1896, the fluoroscope he developed became the standard for medical X-ray examinations . Nevertheless, Edison dropped X-ray research around 1903, even before the death of Clarence Madison Dally, one of his glassblowers . Dally had a habit of testing X-ray tubes on his hands, and acquired a cancer in them so tenacious that both arms were amputated in a futile attempt to save his life . </P>

What was the subject of the first xray
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