The Böhm harmonica company founded in 1850 and located in Klingenthal/Germany was one of the major harmonica manufactures in the first half of the twenties century.
The company produced quite an amount of innovative harmonicas. One innovation is described in the patent #DE470354 by Otto Hermann Böhm granted in 1929.
Böhm Blue Bird also based on the patent from 1929 (from John Whiteman’s collection)
Pat Missin has a detailed technical explanation including pictures showing how this invention works. He also mentions that a similar idea was already patented (# US443607A) in 1890 by John Oefinger and Benjamin F. Butler of Greenfield, Massachusetts.
In 1937 Böhm applied for patent #DE703 133. It was granted in 1941. The idea there was to use the slider to cover one set of reeds instead of shifting an entire reed plate as described in the earlier patent. This functionality was realized in the Böhm tremolo chromatic.