The bodily parts that are formed in the seed

A still more perfect knowledge of how all the parts of the body are nourished is to be had when we consider how they were originally formed from the seed.

Until now, I have been unwilling to put my views on this topic into writing, because I have not yet been able to make enough observations to test all the thoughts I have had on the matter.

I specify nothing on the shape and arrangement of the particles of the seed.

Plants, being hard and solid, can have its parts arranged and situated in a particular way which cannot be altered without making them useless.

But the situation in the case of seed in animals and humans is quite different, for this is quite fluid and is usually produced in the copulation between the two sexes, being, it seems, an unorganised mixture of two liquids, which act on each other like a kind of yeast, heating one another so that some of the particles acquire the same degree of agitation as fire, expanding and pressing on the others, and in this way putting them gradually into the state required for the formation of parts of the body.

These two liquids need not be very different from one another for this purpose.

Old dough can make new dough swell.

The scum formed on beer is able to serve as yeast for making more beer

Likewise, the seeds of the two sexes, when mixed together, serve as yeast to one another.

The first thing that happens in this mixture of seed, and which makes all the drops cease to resemble one another, is that the heat generated there – which acts in the same way as does new wine when it ferments, or as hay which is stored before it is dry – causes some of the particles to collect in a part of the space containing them, and then makes them expand, pressing against the others. This is how the heart begins to be formed.

These tiny parts then expand and continue their movement in a straight line.

Its heart has now begun to form. This resists them.

They slowly move away and go to where the brain stem will later be formed.

In the process, they displace others which move around in a circle to occupy the place vacated by them in the heart.

After the brief time needed for them to collect in the heart, these in turn expand and move away, following the same path as the former.

This results in some of the former group which are still in the same position – together with others that have moved in from elsewhere to take the place of those that have left in the meantime – moving into the heart.

The beating of the heart, or the pulse, consists in this repeating expansion.

this material that passes into the heart, that

The violent agitation of the heat makes the blood:

• expand and move apart and become separated
• gather and press and bump against one another and divide into many extremely tiny branches.

These branches remain so close to one another.

• Only the fire-aether can occupy the spaces remaining around them.

The particles that, in leaving the heart, join together with one another in this way, never leave the circuit by which they return to it, in contrast to the many other particles that penetrate the mass of seed more easily, and from the seed new particles continue to move towards the heart, until it is all used up.

This is why the blood of all animals is red, as explained in:

• Dioptrics and Principles of Philosophy on the nature of light
• Meteors on the nature of colours

We see light through the pressure exerted by the air-aether [2nd element] which are made up of many little corpuscles all touching one another.

These corpuscles have 2 motions:

1. They follow a straight line towards our eyes

This gives us the sensation of light.

2. They turn around their own centres.

If their rotation speed is much less than that of their rectilinear motion, the body which they come from appears blue.

If they turn much more quickly, it looks red to us.

Blood particles have branches so delicate and so close to one another. Only the fire-aether can go around them.

On the surface of the blood, the air-aether meets the fire-aether.

The fire-aether continually:

• passes very quickly obliquely from one blood-pore to the next
• moves in the opposite direction to the air-aether

This forces the air-aether to rotate faster, creating a red color.

This is why hot iron and burning coals appear red – their pores are filled only with the fire-aether.

• Their pores are not as small as those of blood.
• This is why their shade of red is different from that of blood.

As soon as the heart begins to form in this way, the decompressed blood which leaves it takes its course in a straight line in the direction in which it is freest to move, which is the region where the brain will later be formed.

The path taken by the blood begins to form the upper part of the aorta.

Now because of the resistance offered by the parts of the seed that it encounters, the blood does not travel very far in a straight line before it is pushed back towards the heart along the same path by which it came. But it cannot go back down this path because the way is blocked by the new blood that the heart is producing.

This forces it to return somewhat to the side opposite to that of the new material entering the heart, and it is on this side, where the spine will later develop, that it makes its way towards the region where the parts that will serve for generation will be formed, and the path that it takes in its descent is the lower part of the aorta. But because parts of the seed also press on it from this side, they resist the movement of the blood, and because the heart continually sends new blood to the top and bottom of this artery, this blood is forced to take a circular path back towards the heart, via the side furthest from the spine, where the chest will later develop.

The path that the blood takes in returning thus to the heart is what we afterwards call the vena cava. I would not add anything here concerning the formation of the heart, if it had only a single ventricle like that of fish; but because there are two ventricles in all animals that respire, it is necessary that I try to say how the second is 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, and that the blood that leaves from this left ventricle runs first towards the place where the brain is formed, then from there to the opposite spot, where the generative parts are formed, and that in descending from the brain to there, they pass principally between the heart and the place where the spinal column is formed, and 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, and because this expansion pushes the matter surrounding it, 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; but I say that 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.

And 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; and 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.

I would add here also a word concerning the particles that I have called ‘aerial’, for by that term I do not understand all 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. And 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. For one must realise that, while 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, the finer ones, which make up the spirits, proceed a little further, and get to the spot where the brain will subsequently be. Next 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 subse- quently 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, which is why they also try to move towards the other sides. And 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. I say that they turn towards the base of the brain, because they are  reflected off its upper part. And I say that 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. But so that we might know the cause of their diversity, and of every- thing peculiar to each of them, it should be noted that the only thing that can make these particles of spirit separate and take their course left and right towards the front of the head is their extreme smallness or extreme weight, or their having shapes that retard or facilitate their movement.

And I observe only one notable difference among those that are extremely small, namely that some – those that I called ‘aerial’ above – have very irregular and impeding shapes, whereas others have shapes that are more regular and slippery, so that they are more suited to making up fine materials such as brandy or smelling salts than air. And in examining the properties of the aerial particles, it is easily estab- lished that it is these that must follow the lowest path of all, that closest to the front of the head, where they begin to form the organs of smell; just as it is those having the most regular and slippery figures that, flowing  above the aerial ones, proceed by turning towards the front of the head, where they begin to form the eyes.

I also observe only one notable difference between the larger particles of spirits, which is that some have shapes which are not really as obstruc- tive as those of the aerial ones (for, because of their size, they will have mixed very little with spirits), but nevertheless irregular and unequal, which brings it about that they cannot move one after the other but, being surrounded by fine matter, they follow its agitation; and thus having more force than any of the others, because they are more massive, they leave the middle of the brain by a shorter route, and head towards the ears, where, taking away with them some aerial particles, they begin to form the organs of hearing. The others, on the contrary, have regular and slippery shapes, which is why they act together so easily in moving one after the other, just like the particles of water, and consequently their motion is slower than that of the rest of the spirits, which means that they descend through the base of the brain towards the tongue, the throat, and the palate, where they prepare the way for the nerves needed to make up the organs of taste. As well as these four notable differences – which result in certain particles of spirits leaving their body and in this way beginning to form the organs of smell, of vision, of hearing, and of taste – I note that the  others separate gradually as they find pores in the seed through which they can pass; and it is not necessary for this that there be any differences between them, only that those that collide closest to the pores enter them, while the others run their course together along the spinal column, until they too encounter other pores through which they run into all the interior parts of the seed, and trace passages of nerves there which are used by the sense of touch.

Moreover, so that the knowledge that one has of the shape of already-formed animals does not prevent one from conceiving of that which they have at the beginning of their formation, the seed must be considered as a mass in which the first thing to be formed is the heart, and around it is, on the one side the vena cava, and on the other the aorta, which are joined at their two ends, so that the end towards which the openings of the heart are turned marks the side where the head will be, and the other marks that of the internal parts. After this, the spirits have moved a little higher than the blood towards the head where, being collected in some quantity, they have taken their course gradually along the artery, and as close to the surface of the seed as their force is able to carry them; and while they followed this course, their small parts have been able to pass through all the other paths that are easier for them than those where they are. But they have not found any such paths above the spinal column, because the whole body of spirits withdraws towards there, to the extent that its force  allows it; nor have they found one directly below, because the aorta is there; so they have only flowed to the right and the left, towards the internal parts of the seed.

Except only that at the exit from the head, they have been able to with- draw a little inside and outside, because the marrow of the spinal column is less bulky than the head, and they are able to find some space in the former. And this is the reason why the nerves that leave the two first junctures of the spinal column have a different origin from the others.

Now I say that the spirits, which prepare the way for the nerves in the seed, have taken their course there towards the internal parts alone, because the external ones, being pressed against the surface of the womb, did not have any passages free to receive them, but they did find enough free ones towards the front of the head. This is why, before leaving them, some became separated from others without their being of a different nature, and traced the path of the nerves that lead to the muscles of the eyes, the temples, and other neighbouring spots, and then also the paths of the nerves that go to the gums, the stomach, the intestines, the heart, and to the membranes of other internal parts that are subsequently formed.

For all that, the spirits that flowed outside the head found pores on both sides of the length of the spinal column, and by these means they distinguished its joints, and became widely distributed all around the mass of the seed, now no longer round but oblong, because the force of  the blood and spirits that have passed through the heart to the head have of necessity stretched it more in that direction than in the other. And it remains here only to note that the last place in the seed at which the spirits can arrive in following their course in this way is that where the navel must be: I shall speak of this when the time comes. But order demands that, after having described the course of the spirits, I explain also how the arteries and the veins spread out their branches in all parts of the seed.

The more blood is produced in the heart, the greater the force with which it expands, and in this way it advances further. And it can only advance thus towards the places where there are parts of the seed that are disposed to make room for them, and then towards the heart via the vein joined to the artery by which this blood arrives, because they cannot take any other route than this. Two new small branches are thus formed, one in the vein and the other in the artery whose extremities are joined, and which go together to occupy the place vacated by these small parts of the seed. This makes the branches that have already been formed stretch out as far as this, for unless this happened their extremities would separate. And this occurs above all because all the tiny parts of the seed are suited to flowing thus towards the heart – or at least, if there are some that are not suited, they are easily pushed back towards the surface, so that there are none below this surface in the area where the spirits spread out  that do not in their turn proceed to the heart. And this is the reason why the veins and the arteries extend their branches equally there in every direction.

And the truth of this should not be doubted, although one does not usually see as many arteries as veins in the bodies of animals. The reason that the latter appear so much more numerous than the former is that the blood usually comes to rest in the small veins as well as in the large ones even after the animal is dead, because the whole membrane around them contracts almost uniformly. The blood in the arteries, on the other hand, never comes to rest in their small branches, for being pushed by the diastole, it moves quickly in the veins, otherwise it falls back into the largest arteries at the moment of systole, because their tubes remain open; and thus their smallest branches cannot be seen, any more than can the white veins, called ‘lacteous veins’, which Aselli discovered a short time ago in the mesentery, where one would only observe them if one opened up a living animal some time after it had eaten.

We can yet consider here more particularly the distribution of the principal veins and arteries, because it relies on what has already been said concerning the movement of the blood and the spirits. Thus the first agitation of the heart, which had still only begun to form, caused the tiny parts of the seed closest to it to flow to the openings in its ventricles.

By these means were formed what are called the ‘coronary’ arteries and veins, because they completely surround it like a garland [Lat: corona]. And one should be surprised to find that it has not often been noticed that there is only one coronary vein, even though there are two arteries: for this single vein can have enough branches for it to be joined to all the ends of the branches of the two arteries. And it is not surprising that the tiny parts of the seed which come from all around the heart have taken their course towards a single spot in order to enter its right ventricle, at the same time as the blood leaving the left ventricle has taken its course through two different places in order to occupy the spot vacated by them. When the expanded blood in the heart has left it, and has taken its course in a straight line, it first pushes a large enough portion of the seed a little further than it was, towards the top of the womb, and by these means the other parts of the seed below this portion have been forced to descend towards the sides, which has brought it about that those towards the sides flowed from there towards the heart. And thus these large veins and arteries, which nourish the arms of humans, or the front legs of brute  animals, or finally the wings of birds, have begun to form.

What is more, the portion of the seed from which the head will be formed, pushed thus by the blood that comes from the heart, is made a little more solid at its surface than inside it, because it has been squeezed on the one side by the blood which pushes it, and on all the others by the rest of the seed which it pushes: which is why this blood cannot at first penetrate as far as the centre; and the spirits alone enter there, where they form the space in the head in the way already explained.

On this matter, it must be noted that these spirits having taken their course from the middle of the head towards three different sides, namely towards the back where they trace the spinal column, and also via the shoulder towards the left and right front sides, the matter whose place they took has been able to be drawn towards the top of the skull, in the three spaces that the three sides mark out; and from there taking its course through the two sides of the spinal column towards the heart, it makes room for the three principal branches of the great ‘triangular vessel’ that is between the folds of membrane that envelop the brain, and which has the characteristic that it brings together the functions of the artery and the vein. For the matter that was in that place, being pushed by the spirits, leaves there so easily and quickly that the branches of the arteries joined to the branches of the veins through which it flows towards the heart, are merged with these in forming this vessel, which afterwards  extends its tiny channels on all sides inside the skull, so that it alone provides almost all the nourishment to the brain.

Nevertheless, the blood in the principal tube of the aorta, which comes in a straight line from the heart, cannot penetrate the base of the head at first, because the tiny parts of the seed are too closely packed there and exactly below a spot where afterwards a gland will be formed, which physicians have supposed serves only to receive the pituita from the brain.

It exerts itself everywhere against the small parts of the seed, which resist it, and gradually drives some out, which flow from the side towards the veins sufficiently distant from there. By these means are formed those tiny branches of the arteries called the Rets admirabilus, which are more easily observed in animals than in humans, and which seem not to be joined to the veins.

Next, it was also raised higher towards the top of the head, in the neighbourhood of the spot through which the spirits enter the head, around which it has made innumerable tiny channels, which are so many tiny arteries that have begun to form the small membrane called the infundibulum, and then that which covers the duct of the ventricle that is behind the brain, and also the small tissues called the ‘choroid’ tissues, which are in the two cavities in front; and after that, being collected around the spot where the small gland called the ‘pineal gland’ will be formed, they entered all together the middle of the triangular vessel which nourishes the brain.

I do not need to explain in detail anything more about the formation of the other veins and arteries, because I see nothing in particular of note, and they are all produced by this general cause, namely, that when some small part of the seed goes towards the heart, the tiny channel that it makes in going there is a vein, and that made by the blood, coming from the heart in order to take its place, is an artery; so that, when these tiny channels are slightly separated from one another, the vein and the artery seem separated, because the ends of the arteries are not seen.

And in this initial stage, several different causes can make these tiny channels turn, or make one divide into two, or two collect into one, which results in the difference that one sees between the distribution of veins and that of arteries. But this does not prevent them always retaining the same connection between the ends of their branches, because the blood which passes continually through these branches maintains it.

Moreover, the branches through which this connection is made are found in all places in the body and not only in their extremities, for even if one cuts one’s foot or one’s hand, one does not thereby impede the blood in the leg, or in the arm.

I will add here just three examples of the division, the growth, and the joining of these tiny channels. There was no doubt at the beginning only a single tube, which carried the spirits in a straight line from the heart to the brain, but the tracheal artery, through which the respiratory air passes, is formed later (so I shall say more in its proper place), and the air that it contains having more force to rise following this straight line than does the blood that comes from the heart, this tube came to be divided into two branches, namely, what are called the ‘carotid’ arteries.

The 2 veins called the ‘spermatic’ veins were embedded in the vena cava, each as low as the other, at the time of their first formation, but the agitation of the aorta, when the liver and the vena cava are turned to the right side, is the reason why the spot where the left spermatic vein was embedded is raised gradually as far as the emulgent vessel while that on the right remains unchanged; just as, on the other hand, as a result of the same cause, the vein called the ‘adipose’, of the left kidney, is raised from the emulgent vessel, where it was first, to the trunk of the vena cava, while the expansion of the liver causes the right one to be lowered. I mean what I say when I tell you that this is something I have long sought, and indeed something in which I had the least hope of success, although it has not stopped others.

The arteries and the veins that descend in mammals have a very different origin from those that are called ‘epigastric’, which come from the bottom up towards the abdomen. Nevertheless, several of their branches are joined vein to vein, and artery to artery, towards the navel.

This happens because the former spot is the last from which the parts of the seed run towards the heart, because they have a longer route to traverse to arrive there; and because having done exactly this, the blood –  as much in rising through the veins in mammals as in descending through the epigastrics – which comes from one part or another through the arteries which accompany them, drives out the parts of the seed which are between the two, until it has gradually pushed them all through the very tiny passages in the veins, and in this way the principal branches of the arteries find themselves joined to the opposite arteries, and those of the veins to veins.