The most common things that we do with our hands are really wonderful. Watch one as he is buttoning up his coat: how easily his fingers do it; and yet it is a wonderful performance. Suppose a man should try to make a machine, shaped like the hand, that would do the same thing, do you think that he would succeed? It would be very strange if he did. Suppose, however, that, after working a long time, he did really succeed, and that you saw his machine, with its fingers and thumb, put a button through a button-hole in the same way that you do it with your fingers. Do you think that it could manage buttons of all sizes, large, middle-sized, and small? No; it could only button those that are of one size. The different sized buttons would require different machines; and, besides, a machine that could button up could not unbutton. But your hand is a machine that, besides buttoning and unbuttoning buttons of various sizes, is doing continually a great variety of things that machines can not do. No machine can take up a pen and write, or even move a stick about as your hand can. When some ingenious man makes a machine that can do any one thing like what the hand does, it excites our wonder, and we say, How curious! how wonderful! how much like a hand it works!
The hand an instrument of feeling.
But the hand is not merely a machine that performs a great many motions; it is also an instrument with which the mind feels things. And what a delicate instrument it is for this purpose! How small are the things that you sometimes feel with the point of the finger! As you pass it over a smooth surface, the slightest roughness is felt. A great deal of knowledge, as I told you in Chapter XIV., gets into your mind through the tips of your fingers. Messages are going from them continually by the nerves to the mind in the brain. The blind, I have told you, read with their fingers. They pass them over raised letters, and the nerves of the fingers tell the mind what the letters are, just as the nerves of your eyes are now telling your mind what the letters are in this book.
The hand guided by the touch.
Now, while the hand is performing its different motions as a machine, it is generally very much guided by this sense of touch. If your hand had no feeling in it, it would make awkward business even in such a simple operation as buttoning; and it could not do it at all if you did not look on all the time that it was doing it. Your eye-nerves would have to take the place of your finger-nerves, as in the reading of the blind the finger-nerves take the place of the eye-nerves. As it is, you need not look at your fingers while they are buttoning, for they are guided by the feeling that is in them.
There was once a woman who lost the use of one arm, and at the same time lost all her feeling in the other. She had a baby to take care of. She could hold it with the arm that had no feeling, because she could work the muscles in that arm, but she could not do it without looking at it all the time. If she looked away, the arm would stop holding the baby and let it fall, for it could not feel that it was there. In her case the eye-nerves had to keep watch in place of the arm-nerves that could not feel.
How it differs from machines made by man.
You see that the hand is different from the machines that man makes in two things—in the variety of things that it can do, and in the connection which it has with the mind by the nerves. While the mind, by the nerves, makes it do things, it knows by other nerves all the time whether it is doing them right.
See, now, what are the parts of this wonderful set of machinery. There are in the hand and arm thirty bones. There are about fifty muscles, and all these are connected with the brain by nerves. It is by them that the mind makes the muscles perform all the various motions of the hand and fingers, and then there are other nerves that tell the mind what is felt in any part of this machinery.