The Sensible Bodies and Insensible Particles

196. The soul perceives only in so far as it is in the brain

The soul does not perceive in so far as it is in each member of the body.

It can only perceive when it is in the brain. This is where the nerves, by their movements, convey to the brain the actions of the external objects that touch the parts of the body in which they are inserted.

There are 3 proofs for this:

1. There are various maladies which affect the brain alone. Yet these bring disorder on our senses.

This is the same way that sleep only affects the brain. Yet it takes from us the faculty of perception which afterwards is restored to us in our waking state.

2. The obstruction to the movement of the nerves that extend from the brain to the end of those nerves can take away sensation from the part of the body.

This happens even if there is no disease in the brain [or in the parts where the organs of the external senses are].

3. We sometimes feel pain in certain body parts even if the real cause is somewhere nearer the brain.

A girl suffered from a bad ulcer in the hand. She had her eyes bandaged whenever the surgeon came to dress it as she was unable to bear the sight of the dressing of the sore.

The gangrene spread. After a few days, the arm was amputated from the elbow without the girl’s knowledge.

Linen cloths tied one above the other were substituted in place of the part amputated, so that she remained for some time without knowing that the operation had been performed.

Meanwhile, she complained of feeling various pains, sometimes in one finger of the hand that was cut off, and sometimes in another.

The only explanation is that the nerves which before stretched from the brain to the hand, but now ended in near the elbow, were moved in the same way as they did before the amputation.

This movement still impressed on the mind in the brain the sensation of pain in the finger.

This clearly shows that the pain of the hand is not felt by the mind in so far as it is in the hand, but in so far as it is in the brain.

197. The mind can be excited by the various sensations from the motion of body.

The motions of the body alone are sufficient to excite all sorts of thoughts in the mind, even if those motions do not resemble those thoughts.

Confused thoughts are called sensations (SENSUS, SENSATIONES). These especially can give rise to such thoughts.

Words, whether uttered or written, excite in our minds all kinds of thoughts and emotions.

Someone will object that:

• writing and speech do not immediately excite any passions in the mind
• the imaginations of things are different from the letters and sounds

But what about the sensations of pain and titillation?

The motion of a sword that almost cuts our skin gives us a real fearful sensation even if the sword would not really cut our skin.

On this, we may conclude that our mind is easily excited to enter sensations that are not real.