As the trained touch takes the place of sight, why should it not, to some extent, take the place of hearing, since sounds set up, in sonorous bodies, vibrations perceptible by touch?  By placing the hand on the body of a ’cello one can distinguish without the use of eye or ear, merely by the way in which the wood vibrates and trembles, whether the sound given out is sharp or flat, whether it is drawn from the treble string or the bass.  If our touch were trained to note these differences, no doubt we might in time become so sensitive as to hear a whole tune by means of our fingers.  But if we admit this, it is clear that one could easily speak to the deaf by means of music; for tone and measure are no less capable of regular combination than voice and articulation, so that they might be used as the elements of speech.

There are exercises by which the sense of touch is blunted and deadened, and others which sharpen it and make it delicate and discriminating.  The former, which employ much movement and force for the continued impression of hard bodies, make the skin hard and thick, and deprive it of its natural sensitiveness.  The latter are those which give variety to this feeling, by slight and repeated contact, so that the mind is attentive to constantly recurring impressions, and readily learns to discern their variations.  This difference is clear in the use of musical instruments.  The harsh and painful touch of the ’cello, bass-viol, and even of the violin, hardens the finger-tips, although it gives flexibility to the fingers.  The soft and smooth touch of the harpsichord makes the fingers both flexible and sensitive.  In this respect the harpsichord is to be preferred.

The skin protects the rest of the body, so it is very important to harden it to the effects of the air that it may be able to bear its changes.  With regard to this I may say I would not have the hand roughened by too servile application to the same kind of work, nor should the skin of the hand become hardened so as to lose its delicate sense of touch which keeps the body informed of what is going on, and by the kind of contact sometimes makes us shudder in different ways even in the dark.

Why should my pupil be always compelled to wear the skin of an ox under his foot?  What harm would come of it if his own skin could serve him at need as a sole.  It is clear that a delicate skin could never be of any use in this way, and may often do harm.  The Genevese, aroused at midnight by their enemies in the depth of winter, seized their guns rather than their shoes.  Who can tell whether the town would have escaped capture if its citizens had not been able to go barefoot?