Typical of the offerings of so many makers during the 1800s, the Demas treadle-lathe and scroll saw was intended for use by the home hobbyist. The design was very similar to a more successful example, that made by Goodell Pratt (Millers Falls) in America and sold in the England - right into the 1950s - branded as the "Hobbies" by the Hobbies Ltd. of Dereham in Norfolk, whose catalogues promoted the hobby with plans, drawings and projects for fret work.
Another US maker of treadle scroll saws was the lathe and drill maker Barnes, with both companies advertising widely and increasing the machines' popularity to both amateur and professional craftsmen.
Like the Goodell Pratt, this would have been a very small machine with an almost toy-like appearance, though it was constructed in cast iron. The centre height was around 2.5 to 3 inches, the capacity between centres around 14 to 16 inches and its height, from floor to the bed, only 28 inches - and with a width of perhaps 25 inches. 
Limited to a single spindle speed - the Goodel Pratt had two and a jockey pulley to adjust the tension of the round leather belt, a feature missing on the low-cost Dumas - the machine would have been restricted in its capabilities. However, this would probably have mattered little to the new owner, especially in the early days of playing with it.
Learn more about scroll saws on this well-presented website.