U.S. Blues Field Manual
Section 1.2.3.4(a) How to Sing the Blues

24. Some additional notes for the advanced Bluesman. You need a guitar or Mississippi saxophone (harmonica) to sing the blues. If you don't have these tools, you really got the blues ‘cause now all you can do is clap your hands and stomp your foot! And what if you lost your leg or arm jumping from a train, now you can't even do that, see how the blues is, it just goes on and on and gets worse as it goes! Sing it to me, Bluesman!