Apparently well-known enough to rate a Wikipedia entry, the book sounds fascinating (it was later turned into a movie, 7 Faces of Dr Lao starring Tony Randall and with special effects by George Pal).
I haven't read it yet, but I picked it up because of the cover, and bought it based on the few illustrations inside, drawn by a master: Boris Artzybasheff. They are terrifically surreal, and it's hard to imagine the book living up to their promise.
I don't think they were originally in color, but the Wikipedia article shows a slightly different treatment for the cover art. Also, possibly reflecting his fame in 1964 (the year before he died), the cover of my copy says "with additional interpretations by Boris Artzybasheff."
Anyway, enough of that. Just look at this art! This is all of it -- the two-page spread had the single-page illustrations on either wide of it, and the last illustration was on the final page of the book. Also, each was listed on a separate page, with titles like "A Lecture on Lusus Naturae" (on the illustration above) and "Soft Music on the Piccolo" (on the two-page spread).