If you want to see the very best of Gauguin and Matisse, go east. That was the case in 1914 and it’s still true today. The reason, then and now, lay in the collecting habits, both discerning and extravagantly acquisitive, of two men: Sergei Shchukin and Ivan Morozov. The first of these has already been the subject of a notable book by Natalya Semenova; the present work is its sequel.