This is a very unique and interesting instrument. It has a range of one octave. The notes are not sorted in chromatic order. The slider serves to move to the next adjacent note which is usually a half step higher (the exception is the last channel A->E) .
It was most likely manufactured by Seydel. Unfortunately, the harmonica came without a box and there is no manufacturer name anywhere on the covers. One thing that points me to Seydel is the slide button. Comparing it to a Seydel/Bandmaster chromatic harmonica button it looks identical. Jugging by the lettering on the covers, my best guess it that it was produced in the late 1930s.
Each channel consists of two blow reeds. This is a contrast to a “regular” chromatic harmonica which comes with blow and draw notes .
Each channel contains two reeds, tuned exactly one octave apart. This concept is similar to a standard Bass harmonica which also comes with two blow notes (one octave apart) per channel .
A similar concept was picked up years later by Suzuki when they came out with their own S-48B Bass Chromatic.
Chromatic Harmonica History 