Here is a journal publication on Birch Bark Extract from, interstingly enough, the Russian Academy of Medical Sciences published by:
O. A. Rapp1, V. G. Pashinskii (1) and V. S. Chuchalin (2)
(1) Research Institute of Pharmacology, Tomsk Scientific Center, Russian Academy of Medical Sciences, Tomsk, Russia (2) Siberian State Medical University, Tomsk, Russia
It's on a stufy re - the spleen, thymus and adrenal gland.