SEATTLE—Exuberantly tapping the glass of the murky case as he tried to attract the attention of hospital staff, transplant patient Robert McCarthy appeared to be barely able to contain his excitement Tuesday while gesturing to the organ he wanted in the surgical wing lobby’s fresh kidney tank. “I want that one, the big one in the corner,” said McCarthy, 46, motioning toward a lively and perfectly bean-shaped renal organ, which medical personnel estimated to be a sprightly 15 years old. “Wow, would you look at the nephrons on that guy? Just one of him ought to be plenty for me—no wonder they say you don’t really need two. Honestly, any of them would probably be great, except maybe that greyish one bobbing at the top.” McCarthy was then helped into a gaily kidney-patterned surgical bib while a doctor used a sterile net and tongs to scoop out his preferred organ.