How is the Heart Formed?

All animals that respire have 2 ventricles. How is this 2 ventricle heart formed?

The portion of the seed that expands in the heart, before it takes any nourishment from outside, has 2 kinds of particles:

1. Those that move apart and are easily separated
2. Those that join together and attach themselves to one another.

These 2 are found in the blood of all animals.

There are many fewer of those that move apart and are easily separated in the blood of those animals that have only a single ventricle in the heart than in those animals that have two.

Consequently, some of these small particles expand easily. I call them ‘aerial’ particles.

These are the cause of the second ventricle of the heart.

These, after the animal has been formed, are to be found inclined towards the right side.

But at the beginning of its formation, the first ventricle, which is subsequently inclined towards the left side, is rightly located in the middle of the body.

The blood that leaves from this left ventricle runs first towards where the brain is formed.

Then from there it goes to the opposite spot, where the generative parts are formed.

In descending from the brain to there, they pass principally between the heart and the place where the spinal column is formed.

After that, as much from the top as from the bottom, they return to the heart.

As soon as this blood comes near to the heart, it expands partially before entering the left ventricle.

This expansion pushes the matter surrounding it, and so it forms the second ventricle.

It expands because there are several aerial particles in it which facilitate this expansion, and which were not able to break loose as quickly as the others.

It only dilates partially because the portion of the seed which is joined to it, since it left the left ventricle, does not expand so readily as those of its parts that have already been rarefied there.

This is why the expansion of this portion of the seed is postponed until it has entered the left ventricle, to where a part of the blood that has already been rarefied in the right ventricle returns.

When this blood leaves the right ventricle, those of its particles that are the most agitated and the most energetic enter the aorta.

But the others, which are in part the largest and heaviest, and in part also the most aerial and the softest, begin, in separating, to make up the lung.

For some of the most aerial remain there, and form tiny passages, which afterwards will be the branches of the artery whose extremity is the throat or the windpipe, through which the respiratory air enters.

The largest will return to the left ventricle of the heart. And the path by which they leave the right ventricle is what will later become the pulmonary artery; and that by which they come from there into the left ventricle is what will later become the pulmonary vein.

‘Aerial’ particles does not mean those that are separated from one another, but only those of this number that, without being very agitated or very hard, each have their own motion, which makes the bodies where they are remain rare and not easily condensed.

Because those that make up the air are, for the most part, of such a nature, I call them ‘aerial’.

But there are others, more energetic and finer, like those of brandy, and aqua fortis, or of smelling salts, and many other kinds of thing, which cause the blood to expand and do not prevent it from condensing promptly afterwards.

Many of these are doubtless found in the blood of fish, as well as in that of land animals, and even perhaps in larger quantities: this makes it possible for the least heat to rarefy them.

The most energetic and finest parts, that is, those which are very subtle, as well as very solid and very agitated, which I shall hereafter call ‘spirits’, do not come to a standstill at the beginning of the formation of the lung, as do the majority of the aerial particles; but because they have more force they go further, and pass from the right ventricle of the heart via a passage in the pulmonary artery as far as the aorta.

Moreover, since it is the aerial particles of the seed that are the cause of the formation of a second ventricle in the heart, what prevents a third being formed is that, following the second ventricle, a lung is formed in which the majority of aerial particles come to a standstill.

While the blood coming from the right ventricle is beginning to form  the lung, that leaving the left is also beginning to form other parts, the very first of which, after the heart, being the brain.

The largest parts of the blood leaving the heart go directly in a straight line to the spot in the seed where the lower parts of the head are subsequently formed.

But the finer ones, which make up the spirits, proceed a little further. They get to the spot where the brain will be.

After this, as the blood is reflected back and takes its course down through the aorta, the spirits make their way a little higher on the same side near the spot where the medulla and the spinal column will be.

This occurs because the movement of the blood in the part of the aorta which descends from the heart, to which they are close, agitates the neighbouring seed, and this facilitates their path towards the former side.

Nevertheless, it does not facilitate it to such an extent that they encounter no resistance at all there.

This is why they also try to move towards the other sides.

In this way, while these spirits are advancing towards the spinal column, running up and down the length of it and from there pouring into all the other spots in the seed, those of its particles that excel above the others in some quality are separated from the body and turn right and left to the base of the brain, and towards the front, where they begin to form the sense organs.

They turn towards the base of the brain, because they are reflected off its upper part.

They turn right and left because the space in the middle is occupied by those that have meanwhile come from the heart, and from there make a path to the spinal column, which explains why all the sense organs are double.