Thorens a Swiss manufacturer of high-end audio equipment used to manufacture harmonicas between 1914-1921 and 1938-1952.
One of the three chromatic harmonicas they manufactured caught my attention. Similar to the Koch chromatic, one of their 10 hole chromatics came with an external compression spring.
My assumption is that the 10-hole chromatic with compression spring was the first of the three chromatics Thorens brought to market. I would date it back to the late 1930s.
10-hole Thorens chromatic harmonica with enameled covers and
external compression spring