The Böhm Blue Bird Improved Chromatic is a very interesting instrument. The DRGM 978090 (Deutsches Reichsgebrauchsmuster -> basically the registration to offer a basic copyright protection for design or function ) was registered in 1922.
Böhm came up with a different slider mechanism. The slider will only cover one blow and draw hole and is attached to one spring situated to the top right part of the harmonica. The slider button will be pushed horizontally towards the harmonica.
Some time ago, I saw a chromatic harmonica “Chromonette” (Jos Fischer) with a similar slider mechanism at the Museum of music and winter sports in Klingenthal.
Chromatic Harmonica History 