Hunger and Thirst

Hunger

21. The body also has internal senses.

22. When the strong water in the stomach does not find sufficient food there to consume and exert its powers, the nerve filaments there become more vigorously agitated than usual.

This agitation moves the corresponding parts of the brain. From this, the soul conceives an idea of hunger.

But if that liquid of its temperament is such that it can exert its powers more on certain foods than on others; just as common strong water dissolves metals faster than wax, it also acts in a peculiar way on the nerves of the stomach, whence the soul then conceives an appetite for these foods rather than others to eat.

Here it can be noted the wonderful conformation of this machine, that hunger arises from fasting.

The blood becomes sharper by circulation. And so, the liquid coming from it to the stomach more vigorously agitates the nerves. This explains the craving of pregnant women.

That liquid especially congregates at the bottom of the stomach, and there presses the sensation of hunger.

Thirst

²³ Many parts of that liquid ascend to the throat to moisten it and to fill the pores in the manner of water.

When there is less than needed, they go there no differently than in the manner of air or smoke.

This acts on the nerves in an unusual way, exciting motion in the brain. This makes the soul conceive the idea of thirst.

In the same way, when the blood is purer and finer, and effervesces more quickly, it disposes the nerve there in the manner required to excite the sensation of pleasure; or even if the blood is affected by contrary temperature, it will produce the sensation of sadness.

From these things it is clearly evident what is found in that machine that presents itself to the other internal senses that are inherent in us.

Therefore, it is time to explain how the animal spirits move in the ventricles of the brain and its pores, and what functions depend on them.

²⁴ If perhaps you are seized with a curiosity to examine more closely the pneumatic operations of the organs of Temples, you happen to see how they force air into certain wind chambers; which, as I persuade myself, are deservedly called wind chests:

and how the air from those its prisons bursts forth into various channels, now these, now those, as the organist strikes the keys of the organ with his fingers or the handles of the stops.

²⁵ Think of the heart and arteries as 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.

But external objects, which, insofar as they move the nerves, cause the spirits of those hollows to enter through certain pores of some of them, you will not inappropriately compare to the organist’s fingers, which, according to the various motions with which they depress the keys, cause air to burst forth from the wind chambers into certain tubes.

Just as the harmony of organs does not depend on the disposition of the tubes by which it is excited, which appears externally, nor even on the shape of the wind chambers or other parts, but only on three causes.

Namely, from the air which is breathed out of the bellows, from the tubes which produce sound, and from the distribution of that air into those tubes. Similarly, the functions about which we are speaking here depend in no way on the external figure of all visible parts, which anatomists distinguish in the substance of the brain, nor even on the shape of its hollows, but only on the spirits which flow from the heart, the pores of the brain through which they pass, and the manner in which those spirits are distributed into those pores. So that it is necessary to explain only what is most worthy of note in these three.