The text explains how movement in the human body is facilitated by the nerves and the role of "Living Spirits" traveling from the brain to the muscles. It describes the structure of nerves as thin threads encased in small tubes, and how actions occur similarly to pulling a rope. Some movements, like breathing and walking, happen automatically without conscious thought.
Muscles and Their Function.
The actions of muscles (or nerves) come entirely from the brain, which contains a kind of subtle air or spirit called "Living Spirits." To understand further how movement is facilitated by the nerves: there are three main components of the nerves to be noted. First, their internal structure is like small threads that extend from the brain, where they originate, to the extremities where they are connected. Next, there are small coverings that surround them, forming small tubes that encase these threads. Finally, the "Living Spirits," traveling through these tubes from the brain into the muscles or fibers, keep these threads completely free, and so extended, that the slightest action that moves one part of the body where the extremity of a limb is located, also moves the part of the brain it originates from, similar to how pulling one end of a rope moves the other.
This is also true for certain movements that can occur without the assistance of conscious reason, such as breathing or walking. These rely solely on the configuration of our body parts and their common function, similar to how a clock hand moves due to its spring or weight.
Translation Notes: The term "Living Spirits" refers to an early understanding of nervous transmission rather than actual spirits.