The Momentum of Animal Spirits

How do the animal spirits move in the ventricles of the brain and its pores?

What functions depend on them?

24. I call ‘wind chests’ the pneumatic operations of the pipe organs of Churches

They force air into certain wind chambers.

The air then bursts forth into various channels as the organist strikes the keys of the organ with his fingers or the handles of the stops.

25. The heart and arteries are the bellows of an organ which impel air into its wind chambers

These drive the animal spirits into the hollows of our brain’s machine.

External objects move the nerves by causing the spirits of those hollows to enter through certain pores of some of them.

Such objects are like the organist’s fingers. These depress the keys, causing air to burst forth from the wind chambers into certain tubes.

The harmony of pipe organ does not depend on:

• the disposition of the tubes excited by the air
  • This is external
• the shape of the wind chambers or other parts

The harmony depends only on 3 causes.

1. The air which is breathed out of the bellows

2. The tubes which produce sound

3. The distribution of that air into those tubes.

Similarly, the functions of the animal spirits depend on:

1. The animal spirits which flow from the heart

2. The pores of the brain through which they pass

3. How those spirits are distributed into those pores.

They do not depend on:

• the external shape of all visible parts, which anatomists distinguish in the substance of the brain
• the shape of its hollows