“Invariant,” John R. Pierce, 1944 – A man interviews Homer Green, a man who inoculated himself against change, such that his body will gain immortality through constant regeneration. However, he’s also preserved mentally; meaning, he can no longer acquire memories. The psychologists and historians of a thousand years later study him as a specimen from his time period (c. 1943).
Comments: Themes concerning the past, memory. Read in The Astounding Science Fiction Anthology.
Author: Entry at ISFDB. Not to be confused with John J. Pierce, a later sf writer.