There's a popular science writing trope about how every breath you take contains atoms that were once breathed by X [or, for extra piquancy, in X's dying breath]. I think the one I saw in the late 1960s had X = Archimedes. My first question is, do any of you remember a specific source from the 1900s? (At https://www.newscientist.com/article/mg15020308-500-the-last-word/ someone writes "Is it true that every time we take a breath of air or swallow a mouthful of water, we consume some of the atoms breathed or swallowed by Leonardo da Vinci (as I read in a children’s science book in 1960)?" but doesn't mention the source.) My second question is, what's the best writeup of this that you know? I just borrowed (in e-book form) Sam Kean's recent book "Caesar's Last Breath", which I'm guessing will do a decent job of explaining the science. My third question is, how far back does this sort of observation go? Does it have an attributable original source? (Maybe Kean addresses this; it's a pretty thick book.) If the history of science has a subfield treating history of science popularization, and people do PhD's in it, maybe someone has tracked this trope in all its incarnations, showing how the choice of who gets to play the role of X reflects underlying cultural assumptions about significance and worth. Jim Propp