A manual mixer for mixing and agitating materials for use during surgery, the manual mixer comprising: a body portion having a sidewall portion defining an interior area; a mixing assembly provided in the interior area of the body portion, the mixing assembly including a plunger portion and a variable-diameter spring, the plunger portion including at least one seal for interfacing with the sidewall portion, and the plunger portion including a portion for securely engaging the spring, the variable-diameter spring including a first end portion, a second end portion, and a coil extending between the first end portion and the second end portion thereof, the coil having a variable diameter, the plunger portion being adapted to move upwardly and downwardly within the interior area; a cap portion attached to the sidewall portion of the body portion, the cap portion enclosing the interior area of the body portion, and the cap portion including an aperture that is at least partially threaded; and a stem portion extending through the partially-threaded aperture in the cap portion, the stem portion being interconnected with the plunger portion, and the stem portion being at least partially threaded, wherein threads of the partially-threaded stem portion and threads of the partially-threaded aperture engage one another, and wherein rotation of the stem portion simultaneously rotates the plunger portion and spring, and moves the plunger portion upwardly or downwardly within the interior area, the rotational movement of the plunger portion and variable-diameter spring, and upward and downward movement of the plunger portion serving to mix and agitate the materials provided in the interior area. a body portion having a sidewall portion defining an interior area; a mixing assembly provided in the interior area of the body portion, the mixing assembly including a plunger portion and a variable-diameter spring, the plunger portion including at least one seal for interfacing with the sidewall portion, and the plunger portion including a portion for securely engaging the spring, the variable-diameter spring including a first end portion, a second end portion, and a coil extending between the first end portion and the second end portion thereof, the coil having a variable diameter, the plunger portion being adapted to move upwardly and downwardly within the interior area; a cap portion attached to the sidewall portion of the body portion, the cap portion enclosing the interior area of the body portion, and the cap portion including an aperture that is at least partially threaded; and a stem portion extending through the partially-threaded aperture in the cap portion, the stem portion being interconnected with the plunger portion, and the stem portion being at least partially threaded, wherein threads of the partially-threaded stem portion and threads of the partially-threaded aperture engage one another, and wherein rotation of the stem portion simultaneously rotates the plunger portion and spring, and moves the plunger portion upwardly or downwardly within the interior area, the rotational movement of the plunger portion and variable-diameter spring, and upward and downward movement of the plunger portion serving to mix and agitate the materials provided in the interior area.