ARTIFICIAL LIMBS, &c. Considerable mechanical ingenuity is displayed in supplying substitutes for limbs or organs which accident or any other cause has removed.
The art of the dentist, for instance, calls for no small amount of mechanical skill. First there is the choice of the ivory which, from its colour, texture, and hardness, affords the best imitation of the natural teeth. Then there is the shaping of this ivory to the size and form of the tooth, whether single or double, front or back, upper or under. And lastly there are the remarkable contrivances —by means of golden palates, or springs, or wires, or cement, by which the tooth or mouth ful of teeth are fixed in their places. Expe rience seems to skew that few kinds of cheap ness are so dear as cheap tooth-making: so, great are the difficulties in supplying teeth that will really eat their way through the dif ficulties presented to them. As for the succe daneums and metallic and other cements for stopping decayed teeth, their merit depends more on the quality of the material than on the mode of using. We see from time to time patents for new contrivances in dental surgery, which involve no small amount of ingenuity. One such has been enrolled in 1850 by Mr. Dinsdale, in which the manufac ture of teeth, palates, and gums are described.
An artificial eye is an example of glass manufacture ; the shaping of the glass being much less difficult than the accurate imitation of the cornea and iris by means of pigments and dyes.
All those numerous examples of skill, which may more fittingly be called surgical opera tions than anatomical contrivances, we have nothing to do with here ; but when a mechani cian undertakes to supply an arm, a hand, or a leg, which will render tolerable service as a substitute for one of flesh and blood, we have as much right to claim it as a proof of con structive skill as a loom or a lathe, a plough or a clock. And here we mark how quickly a newly discovered substance becomes broUght within the scope of the operations. Is it caoutchouc? Then will the artificial leg maker find-out where to use it with advantage. Is it gutta penile.? Then will he soon see where the combined elasticity and toughness of that remarkable substance are likely to be valuable. Accordingly we find that many dif
ferent materials are employed, either to give shape to the artificial hand, arm, or leg, or to give smoothness and softness to the surface, or to form the joints for the requisite move ments. Wood, leather, caoutchouc, gutta percha, cork, iron levers, steel springs—all are employed; and much ingenuity is dis played in arranging.
Sir George Cayley, who has exhibited much inventive talent in various mechanical con trivances, has recently made many trials to produce an artificial hand which shall be less costly than those ordinarily constructed. He has made the 'Mechanics' Magazine' the medium of communicating his experience in this matter. His first attempt was in 1845. The son of one of his tenants having lost a hand by accident, Sir George contrived a sub stitute which has in many ways lessened the severity of the privation. The movements of this instrument are derived from the stump; a light frame-work fixes the apparatus to the upper part of the arm ; and a lever connects this frame-work with the artificial hand. The arm is placed within padded rings of metal, which are connected by two long steel bars hinged at the elbow. When the wearer moves his arm by the usual action of the elbow joint, he shifts a small metal bar near the wrist of the machine, which works two cog wheels acting on each other; and these cog wheels bring two steel springs together so as to enable them to grasp an object something in the manner of a thumb and fore-finger. The wheels and springs may either be left exposed, in the metallic state, or may be padded so as to represent a thumb and finger.
It was found that although this artificial hand could be turned round a little way, it could not be turned so much as a quarter of a circle from its horizontal towards a perpen dicular grasp ; and there was, at the same time, no movement equivalent to the usual bending of the wrist, which gives so great a variety of positions to the natural hand. He therefore contrived a new arrangement of mechanism at the wrist, so as to superadd these two movements to those before pos.