This article is from the the official alt.spleen FAQ, by Andrew Stellman with numerous contributions by others.
Andrew says: NOTE: PLEASE DO NOT SEND ANY MAIL TO ME REQUESTING MEDICAL ADVICE! I AM NOT A DOCTOR, AND WILL NOT GIVE YOU ANY USEFUL INFORMATION.
Contrat lawyer Brian Neal (email@example.com) has some information on this. It turns out that the spleen has some contractual obligation with the rest of the body:
"I just exercised my spleen today! Actually, i only gave blood. But I've heard that the spleen contracts to share some more of its blood with the body, when one loses blood..."
This is as yet untested in the courts.