Thumb lancets were introduced in about the 15th C. and soon became the preferred instrument for opening a vein in any part of the body. The double-edged iron or steel blade was placed between two covers or shields, commonly made of horn or tortoise shell, and all joined at the base with a rivet.  The shape of the blade, whether broader or narrower, determined the ease with which the skin and vein could be penetrated. The tiny and delicate lancets were typically carried in a small flat cases of silver, gold, ivory,  horn, tortoise shell, leather, shagreenor mother-of-pearl with hinged tops and separate compartments for each lancet.