Whatever their mechanical perfection, artificial hands can, in fact, possess but one useful quality, that of seizing objects like pincers. In nearly every act performed by the natural fingers are combined flexion, extension, prehension, and many other different movements; this combination no mechanic has ever been able—and probably none ever will be able—to successfully reproduce in an artificial hand. It is, therefore, practically useless that the fingers should be movable, since a less complicated, lighter and stronger hand can be made with fingers rigid, in a half-closed, natural position, articulating the thumb only, which results in a more powerful spring and consequently a greater degree of firm grasping power. The fingers being strengthened with steel plates running through them, reinforced with a covering of rawhide, and securely fastened to the hand, heavy objects may be lifted without danger of the fingers straightening out and the object dropping to the ground.
While we furnish the hand with movable fingers, and the rubber hand with ductile rubber fingers, the wooden hand with rigid fingers and movable thumb is recommended as giving the most practical, durable, and satisfactory service.
The Color
Artificial hands are covered with a delicately tinted enamel, as nearly a flesh color as it is possible to make; but in order that they may be less conspicuous and the illusion more complete a glove should be worn at all times. We furnish a pair of gloves with each hand.
Tools and Implements
Tools and implements in almost limitless variety can be used in an arm in place of the hand. Those most frequently used are the plain hook, double hook, ring, knife, fork, brush, and spoon. People who have never worn arms hardly know what will be of service to them. Special tools are required for special work, and these can be subsequently provided when it has been determined what will be most useful. With all arms with detachable hands, or rubber hands with the palm socket, we furnish a plain hook, knife, fork, and brush, without extra charge, or the price of any of these implements that are not wanted will be deducted from the price of the arm.
Finger Construction
Usually the fingers for artificial hands are made of a single piece of wood, and it is obvious if the finger is curved or flexed that at some point the grain of the wood will be directly across the finger and will quickly break if subjected to any considerable strain. To obviate this difficulty we make the fingers for the wooden hands of two pieces of wood; on one side the grain or fibre runs lengthwise, and on the other crosswise, and between these two pieces of wood is placed a steel plate, and all are firmly riveted together, the steel plate projecting sufficiently to be securely riveted to the hand. The fingers are next entirely covered with rawhide, which, together with the other precautions taken against breakage, make them sufficiently strong to support the weight of the wearer. See No. 300, [page 64].
Partial Amputation of Hand
No. 301 ([page 64]) represents a stump after partial amputation of the hand, leaving free use of thumb, but it is with difficulty that this can be brought in contact with the remaining stump so as to be of service. No. 302 represents, for stumps of this description, a wooden sheath, terminating in immovable fingers partially closed, the hand being attached to the wrist and forearm by means of a leather lacing attachment. The sheath is covered with rawhide and enameled, and the fingers made as shown in No. 300. Price $40.