Before we begin to treat of the faculty of the vegetative soul, it is fitting to presuppose some general notices and instructions that serve for the understanding of this faculty. It is,
then, now to be known that in our soul there are three powers or faculties, of which the first is vegetative, whose office is to nourish and maintain the body, and another that they call sensitive, which is that which gives us sense and movement, and the third is the intellective, which differentiates us from the brutes, and makes us similar to the angels. These three faculties the Creator gave to one simple substance, which is our soul, which is as great a marvel as if he made a creature that were at once angel and horse, since our soul exercises in us the offices of these two so different creatures, since it understands like an angel, and eats and engenders like a horse. For which, some philosophers did not admit this, rather they said that these three faculties of our soul were three souls, which they placed in diverse places of our body, that is to say, the vegetative in the liver, and the sensitive in the heart, and the intellective in the head, and this last Plato said was man, not consenting that a thing so low as our body should be an essential part of man, but a house where the soul dwelt, or a candlestick where the lighted candle of our understanding was placed.
Then according to this aforesaid division, we shall treat first of the faculty of the vegetative soul that we have in common with plants, which also live and maintain themselves as we do, and afterward we shall treat of the other two faculties of the soul, which are the sensitive and intellective. Let this be the first presupposition.
Let the second be what we all know, which is that ordinary maintenance is necessary to conserve life. The reason for this is because the heat of our bodies, by means of which we live, is also no less cause of our death than of our life. For with its efficacy it consumes the substance and the flesh of man, as we see in the sick who through disgust or through diet do not eat, whom after some days we see thin and fleshless. The example of this we see in the lamp that we wish always to burn, where the ardor of the flame little by little goes consuming the oil that sustains it. For which reason it is necessary always to feed it, so that what is always spent may always be repaired. Then the natural heat in our bodies does the same as the flame in the lamp, which always spends and consumes our radical humor, and for this reason it is fitting to restore what is thus spent, with the food that is eaten. Where it must be noted that from this food the body takes for sustaining itself the fatness and oily part that there is in it, so that, if you eat a camuesa apple, nature serves itself from the oily part of it to restore what was lost. And because what is restored is never so perfect as what there was before, from here the radical humor comes little by little to lose of its vigor and virtue and, when this is altogether diminished, life comes to be finished together with it, if some sickness or violence did not anticipate to give it an earlier end.
The third presupposition is that, since the whole body with all its parts has to maintain itself, and it is fitting that maintenance run to all, it is necessary that in all of it there be roads by which the maintenance, and the spirits, and the heat may run to all parts, and thus the Creator traced it full of veins and arteries and nerves, some of them larger and some of them smaller for this effect. So that it is like a city that is all full of streets and of little streets for the passage and service of those who inhabit it. Although I do not know if the example of a very fine net is more accommodated, because thus all our body is interwoven and full, not of one, but of four kinds of nets, as further on we shall declare. Which appears more
clearly in the leaves of trees, especially when they are large, in which we see so many little threads, some larger and others thinner than hairs, which are the weaving with which the leaf is sustained and maintained. And not content with this, the Creator ordained that the whole body should be, as the physicians call it, transpirable, which is to be all full of pores so that there may be communication from some members to others.
Let the fourth be that that most wise artificer placed three necessary faculties in all the members for their maintenance, which they call attractive, conversive, and expulsive. For each member attracts from the veins, which are carriers of the maintenance, what is necessary for its nutrition, and afterward converts it into its substance and, if it has some superfluity that is not fitting for it, it casts it away from itself. But among these three faculties the first is more admirable, which is the attractive. For since in that mass of the blood there go the four humors of which our bodies are composed, which are blood, phlegm, choler, and melancholy, each member, as if it had judgment and sense, takes what is fitting to its nature, and does not touch the rest. And according to this, the bone, which is hard and solid, which also maintains itself and grows like the other members, as we see in the bones of children that go growing with age, takes from that mass the cold and dry humor, because this is more natural and more proportioned to its substance. And so do all the others, each one in its manner. For this is placed the example of the magnet stone, which, having near itself diverse metals, only attracts iron to itself, the others left aside. Then he who gave such virtue to this stone, also gave it to the members, so that each one should take for itself from that mass what was more conformable to its substance. The same we see in the choice of foods that animals make, because, if you should put together a piece of meat, and a little wheat, and another of grass, the sheep will attend to the grass, and the dog to the meat, and the hen to the wheat. Then he who gave to the animals this natural knowledge of the food that is fitting for them, also gave to the members this same instinct and nature, so that each one should take from that mass what was most fitting for it.
Let the fifth be that in this our body there is that brotherhood that the Apostle so many times commends to us, because all the members and senses serve one another, and all serve the common good, which is the conservation of the whole, but this with such order, that the less noble serve the more noble, and thus the first digestion of the food, which is made in the teeth, serves the second, which is made in the stomach, and this one the intestines, and these the liver, and the liver the heart and all the body, and the heart the brain, which is the most noble member (where the senate and the consuls reside, which are the exterior and interior senses) and thus it also provides sense to all the members, so that by this example it may be seen how the preeminence and dignity of the greater ones must be employed in the government and profit of the lesser ones.
There is also here another providence of the Creator, who does not consent that in this his house there be anything wasted and without profit, just as he did not wish that there be in the world an empty place, nor did he consent that the pieces of bread that had remained from the miracle of the five loaves be lost. Then for this reason he traced the government of our body in such manner that what in one part was left over as superfluous, in another should be necessary, as we see in the melancholy that the liver rejects, which serves as maintenance for the spleen, which
is a less noble member; as we see in the houses of the rich, where the servants maintain themselves from what is left over from the tables of their lords. And the same we see in the other superfluities that the liver, and the stomach, cast away from themselves.
Over all that has been said, another thing must be adverted to that no less declares the counsel of divine providence, and it is that, as Aristotle says, nature (that is, the author of it) does not make its works similar to a knife that there was on the island of Delos, which served for many offices and instruments, but for each office it ordered its own instrument, the eyes for seeing alone, the ears for hearing, the noses for smelling, etc. In which is seen the royalty of this house of our body, which the Creator fabricated for the dwelling of our soul, as for a thing created to his image and likeness. For we see that in a house of a squire or of some poor hidalgo many times there are no more than one or two servants who serve in all the offices of the house, but in the house of a king we see that there is a great number of offices and of officers, each one deputed for his office, because as the king is rich and powerful, he has the faculty and wealth to sustain all this number of officers. Then applying this to our purpose, there has been no royal house in the world (although it were that of Solomon, which put so great fright in the queen of Sheba) that had as many officers as the royal house of our body has, which the Creator fabricated (according as has been said) for the dwelling of our soul, in which, the offices being so many and so various, there will not be found one officer that has two offices joined together, but each one his own. And if any one seems to have more than one, it is by reason of the diversity of parts that there is in it. This is seen not only in the five exterior senses, but much more in the interior members. And thus he fabricated the stomach to cook the food, the guts to receive it and purge it, the liver to make the mass of the blood, the heart to create the spirits of life, the brains of the brain to create the animal spirits, the veins to distribute the blood, the arteries to carry the vital spirits, and the nerves to distribute the animal ones, and thus many others that we could here recount. All of which serves not only to declare the order of divine providence, but also for instruction and foundation of medicine. For, the quality and condition of the parts of the body being understood, and the dependence that they have one on another, the physicians know where they must apply the medicines, and in what place they must command the bleedings to be made, and where they must give the cautery of fire, with the rest. For we have already seen a very grave pain of sciatica that was in the hip of the thigh cured by giving a cautery in the ear, by the dependence that there is from this superior part to the other inferior one.
These general instructions now proposed, then, we shall descend to treat of the use and office of the principal parts of our body, so that we may see how perfectly they serve the faculty of the vegetative soul, which is to the sustentation of our life. And in the accommodation and proportion of these parts for this end we shall clearly see the artifice and wisdom of divine providence that traced and ordered this.