The Brain

29. Conceive the surface AA, which faces the concavities EE.

It is like a fairly expanded, dense, and intricately woven plexus, resembling a mesh of crosshatched texture.

Each of its filaments is a tube which the spirits enter.

The spirits emanate from gland H. They can easily turn themselves here and there to the different points of that gland, being differently oriented in figure 48 than in 49.

That gland has countless very delicate filaments emerging from it.

Some are ordinarily longer than others.

However, after these filaments have been interwoven in various ways throughout space B, the longer ones descend to D, from there forming the medulla of the nerves, which are then distributed throughout all the limbs.

The main quality of these filaments is that they can be easily folded and bent in various ways solely by the force of the spirits that touch them, just as if they were made of lead or wax. Therefore, they always retain the fold to which they were last affected until another is impressed on them by spirits acting in the opposite manner.

The pores here are the spaces found between these filaments. These spaces can be extended and contracted in various ways by the force of the spirits that enter them.

The shorter filaments of this plexus are received into space CC, where each terminates at the ends of certain vessels there, through which the brain receives nourishment.

The Distribution of Spirits

They are not confined to any place.

As they enter the ventricles of the brain EE through the openings marked by the letter H on the gland, they tend immediately towards the tubes aa, which are directly opposed to them.

If these tubes are less open to receive all of them, at least the stronger and more agile ones will be received.

Meanwhile, the weaker and residual ones are repelled towards the channels I, K, L, which face the nostrils and palate.

Specifically, they are more agitated towards channel I, through which, when they still have sufficient vigor and find less free exit, they sometimes leap forth so impetuously as to cause tickling in the interior parts of the nostrils, and thus sneezing.

Then, the remaining spirits are received into K and L, where the channels, being very capacious, allow easy passage for them; or if entry is denied there, forcing them to return to the tubes aa, which are on the inner surface of the brain, causes immediate scotoma or vertigo, disturbing the functions of imagination.

Moreover, it is worth noting that while I say the spirits, in their exit from gland H, tend towards the concave spaces or the inner surface of the brain directly opposite to them, I do not mean that they tend directly towards those two points diametrically opposite to them.

The substance of the brain is very soft and pliable. Its cavities would be very narrow and almost entirely closed. This is seen in the brain of a corpse.

But the origin from which those spirits emanate usually abounds with such a copious supply of them that as soon as they enter the ventricles of the brain, they have the strength to remove any surrounding material hindering them, to inflate it, and to intensify all the nerve filaments that proceed from it, just as a slightly stronger wind can spread sails and stretch all the ropes to which they are attached.

Thus, this machine is arranged as to obey all the actions of the spirits equally. It carries the body of a waking person before it. Or at least the spirits have the power to push and thus expand a certain part of the brain, while the others remain motionless and slack, just as we observe slack and relaxed sails when the wind is too weak to fill and fully expand them.

When the machine is arranged in this way, it represents the body of a sleeping person to whom various phantasms occur through dreams.

For example, conceive of the difference between M and N, which we observe between a person half-awake and sleeping, and simultaneously dreaming, as shown in Figure 32.