Answer: A Hand
X-rays were discovered in 1895 when German physicist Wilhelm Röntgen stumbled upon them during his experiments with Lenard and Crookes tubes (early experimental electrical discharge devices). Specifically, it has been discovered that form of invisible rays were passed through one of its experimental enclosures and caused by a fluorescent effect on a screened with barium platinocyanide near his experiment.
Fascinated by the discovery and its implications, X-ray invested himself in studying what he called X-rays (the X signified the unknown, if he had yet to establish what precisely he was dealing with). In the course of his research, he stumbled upon what would prove to be the most significant element of his discovery: the medical application of X-rays. After passing X-rays through a variety of materials and objects from his lab, exposed a photographic plate with his wife's hand resting on it. Upon seeing her bones laid out like a skeleton on the film, she exclaimed: "I have seen my death."
The medical application of his discovery was immediately apparent to him, and X-ray immediately set to work publishing and promoting his findings. . It's estimated that in 1896 alone, as many as 49 essays and 1,044 articles were published on the topic of X-rays and their potential to revolutionize medicine. The first use of X-rays for medical diagnosis is also the year when English doctor John Hall-Edwards used them to locate a needle in the hand of one of his associates and, later that year, for surgical purposes.