Truly a wonderful thing. Shaped like a book, at first I thought this was an old spruce gum box--always something to get excited about!--but then I saw the hole (called a fipple, I've learned) at the base of spine side, and the carved knob at the top, and I realized it might be an extra beautiful slide whistle. Once I had it out of the case at the shop where I spotted it, I discovered to my great delight that the slide was carved out with a big heart inside and one side of the slide beautifully labeled in handwritten ink with notes of the scale.  Pulling the slide out a little while blowing into the mouth hole/slit just around the corner of the fipple produces a strong, clear whistle, which will travel through the notes as marked on the side, as one moves the slide in and out. About as charming a merger of form and function as I've seen, and  a complete delight in every aspect. Seems quite likely this was made as a love token, perhaps for a very musical sweetheart--and it would make a very sweet token of love now to the same. An unusual, very special feeling thing. 

6" l x 4 1/16" w x 1 3/8" d when closed. In beautiful, working condition.Late 19th c. or so, I believe.