The Parts of the Body

7. The Parts of the Body, and Some of Their Functions

The food we eat goes down into the stomach and intestines.

From there, their juice flows into the liver and all the veins, mixing with the blood they contain, and thus increasing its quantity.

All the blood from the veins can easily flow from the vena cava into its right side.

From there, it passes into the lungs through the pulmonary artery. It then returns from the lungs into the left side of the heart through the the pulmonary vein.

Finally, it pass from there into the aorta, whose branches spread throughout the body.

The blood starts from the right cavity of the heart through the pulmonary artery.

The pulmonary artery’s branches are:

• scattered throughout the lungs
• joined to those of the pulmonary vein

Blood goes into the pulmonary vein from the lungs into the left side of the heart.

From there, it goes into the aorta, whose branches:

• spread throughout the rest of the body
• are joined to the branches of the vena cava.

The vena cava again carries the same blood into the right cavity of the heart.

These two cavities are like locks through each of which all the blood passes with each turn it makes in the body.

All the movements of the limbs depend on the muscles.

These muscles are opposed to each other in such a way that when one of them shortens, it pulls towards itself the part of the body that it is attached to.

• This simultaneously lengthens the muscle that is opposed to it.

If that latter muscle shortens, the former lengthens.

• That shortened muscle pulls towards itself the part attached to it.

These muscle movements, as well as all the senses, depend on the nerves.

The nerves are like little threads or small tubes. These all:

• come from the brain
• contain, with the brain, the animal spirits
  • This is a very subtle air or wind

8. The Principle of All These Functions

How do these animal spirits and these nerves contribute to movements and senses?

What is the corporeal Principle that makes them act?

While we are alive, there is a continuous heat in our heart.

It is a kind of fire maintained by the blood from the veins.

This fire is the corporeal principle of all the movements of our limbs.

9. How the Heart Moves

This heat first dilates the blood to fill the cavities of the heart.

This causes the blood to occupy a larger space. It rushes forcefully:

• from the right cavity into the pulmonary artery
• from the left cavity into the aorta.

After this dilation ceases, new blood immediately enters from the vena cava into:

• the right cavity of the heart
• the left cavity from the pulmonary vein.

There are small flaps at the entrances of these 4 vessels. These ensure that the blood can only:

• enter the heart through the last two
• exit through the first two.

The new blood that enters the heart is immediately decompressed in the same way as the previous one.

The pulse or beating of the heart and arteries consists only in this.

• This beating is repeated as many times as new blood enters the heart.

This alone also:

• gives the blood its movement
• makes it flow very quickly through all the arteries and veins

Through this flow, it carries the heat from the heart to all other parts of the body to nourish them.