It is never ending. You find a book, and it leads you to another book.

In this specific case it was Red Medicine: Socialized Healthcare in Soviet Russia using images by Margaret Bourke-White. And looking her up lead me to her wikipedia page which talks about her 1931 book Eyes on Russia. It seems quite interesting, skimming the first parts. I shall put on my list of books to read, potentially even epub.
Red Medicine itself was mentioned in Russian Justice, which was mentioned in This Soviet World

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