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 . <EOS>