Thread:Blaid/@comment-2089817-20121209233629/@comment-1757720-20121212173028

Exactly, my theory is that 100,000 human souls have a higher concentration of Reishi than 20 Arrancar/Shinigami. Notice that Reshi is the particles that make up all spiritual things, in a human being it would be in equal quality, Karakura town is highly saturated in spiritual energy which probably makes it a useful "cooking pot" to that end.