While operating the syringe the narrow blades are brought in contact with the soft flexor sides of the thumb and forefinger, indenting the flesh deeply, and with the least unexpected move on the part of the patient permitting it to slip out of the grasp of the surgeon. Its incapacity for large injections also offers some objection, but for correcting smaller defects it is both practical and compact. It is illustrated in [Fig. 291].
Fig. 291.—Smith All-Metal Drop Syringe.
It is obvious that with the screw drop type of syringe the cold semisolid paraffin mixture contained in its barrel is always under the full command of the operator, nor can there be a plugging of the needle, since the great force that can be exerted with a turn of the piston handle would free it, even if the mixture were of a comparatively high melting point, although the force to be applied would naturally increase in proportion to the hardness of the mass within the syringe.
The turning of the screw piston forces out the contents of the syringe in the form of a white thread of a diameter equal to the diameter of the lumen of the needle.
To facilitate this ejection, the needles should be of ample diameter, not over one inch long and having knife-edged points. Longer needles are not necessary, and only add to the force required to turn the screw handle.
Curved needles, used by some operators, are never needed, and the author does not see how they could be applied at any time in preference to the straight.
As much of the paraffin mixture can be forced out of the syringe as may be desired by screwing the piston down into the barrel.
The piston rod may be graduated in five- or ten-drop divisions, but the operator rarely ever refers to the scale. He judges the amount required by the elevation of the tissues brought about by the presence of the paraffin thus forced under the tissue. Experience soon teaches him the amounts necessary or judicious in each case, always remembering that it is better to do a second and later injection than to hyperinject.
The entire instrument being of metal permits it to be sterilized as readily and in the same manner as any other metallic instrument.