Ask for Codex 001599.
You can also read about a more modern take on negative space in an earlier post.
At last week's annual conference of the Society of Authorship, Reading & Publishing (SHARP), there was a panel titled "The Alchemy of the Page: Transforming Image and Text." One paper described Mark Twain's use of imagery in King Leopold's Soliloquy while the second paper was on the many marginal doodles left behind by Max Beerbohm and G. K. Chesterfield. The panel reminded us of our original manuscript of Chapter Sixteen of Mark Twain's A Tramp Abroad that is full of Twain's doodles.