Unfortunately, that's a bit of a false etymology! According to humorism, black bile [1] comes from the gallbladder, not the spleen. The spleen was supposed to produce yellow bile, an excess of which was thought to cause aggression and anger.
[1] Black bile is actually the source of the term "melancholy" — from the Greek melankholia, from melan- ("black") and kholē ("bile")!
[1] Black bile is actually the source of the term "melancholy" — from the Greek melankholia, from melan- ("black") and kholē ("bile")!