Just wanted to let people know about and interesting book I have come across with regard to embouchure. It is Maurice M. Porter's 'The Embouchure' (London: Boosey & Hawkes, 1967). Whilst the book is directed at wind and brass instruments, there are a few chapters that could apply quite transparently to the mouth organ. They cover a range of topics such as breathing, resonace, stacatto and legato. The book tends to focus on things like the musculature of the mouth and hazards of strain, etc. but tries to extend that knowledge into discussions of playing. I'm still reading it (the diagrams of mouths are slowing me down) so don't ask me for an opinion. It could be of interest to some of you.