The spirit is subtle and Aery substance, raised from the purer blood that it might be a vehicle for the faculties (by whose power the whole body is governed) to all the parts, and the prime instrument for the performance of their office. For they being destitute of its sweet approach do presently cease from action, and as dead do rest from their accustomed labors. From hence it is that making a variety of spirits according to the number of the faculties, they have divided them into three; as one animal, another vital, another natural.

The animal hath taken his seat in the brain; for there it is prepared and made, that from thence conveyed by the nerves is may impart the power of sense and motion to all the rest of the members. An argument hereof is, that in the great cold of winter, whether by the intercepting them in their way, or by the concretion, or as it were freezing of those spirits, the the joints grow stiff, the hands numb, and all the other parts are dull, destitute of their accustomed agility of motion, and quickness of sense. 

It is called Animal not because it is the life, but the cheife and prime instrument thereof; wherefore it hath a most subtle and aery substance: and enjoys diverse names according to the various condition of the sensories or seats of the senses into which it enters; for that which causeth the sight, is named the visive: you may see this by night, rubbing your eyes, as sparkling like fire. That which is conveyed to the auditory passage, is called the auditive or hearing; that which is carried to the instruments of touching, is termed the tactive; and so of the rest.

This animal spirit is made and labored in the windings and foldings of the veins and arteries of the brain, of an exquisite subtile portion of the vital brought thither by the carotid arterie, or sleepy arteries, and sometimes also of the pure air, or sweet vapor drawn in by the nose in breathing. Hence it is, that with ligatures we stop the passage of this spirit, from the parts we intend to cut off. An humor which obstructs or stops its passage, doth the like in apoplexies and palsies, whereby it happens that the members situate under that place do languish and seem dead, sometimes destitute of motion, sometimes wanting both sense and motion.

The vital spirit is next to it in dignity and excellency, which hath its cheife mansion in the left ventricle of the heart, from whence through the channels of the arteries it flows into the whole body, to nourish the heat which resides fixed in the substance of each part, which would perish in short time unless it should be refreshed by heat flowing thither together with the spirit. And because it is the most subtle next to the animal, nature (lest it should vanish away) would have it conteined in the nervous coat of an artery, which is five time more thick, than the coat of the veins, as Galen, out of Herophilus, hath recorded.

It is furnished with matter from the subtile exhalation of the blood, and that air which we draw in breathing. Wherefore it doth easily and quickly perish by immoderate dissipations of the spitituous substance, and great evacuations; so it is easily corrupted by the putrifaction of humors, or breathing in of pestilent air and filthy vapors, which thing is the cause of the so sudden death of those which are infected with the plague. This spirit is often hindered from entering into some part by reason of obstruction, fulness, or great inflammations, whereby it follows that in a short space, by reason of the decay of the fixed and inbred heat, the parts do easily fall into a gangrene and become mortified.

The natural spirit (if such there by any) hath its station in the liver and veins. It is more grosse and dull than the other, and inferior to them in the dignity of the action, and the excellence of the use. The use thereof is to help the concoction both of the whole body, as also of each several parts, and to carry blood and heat to them.

Besides those already mentioned, there are other spirits fixed and implanted in the simular and prime parts of the body, which also are natural, and natives of the same place in which they are seated and placed. And because they are also of an airy and fiery nature, they are so joined or rather united to the native heat, that they can no more be separated from it, than flame from heat; wherefore they with these that flow to them are the principal instruments of the actions, which are performed in each several part; and these fixed spirits have their nourishment and maintenance from the radical and first-bred moisture, which is of an airy and oily substance and is as it were the foundation of these spirits and the inbred heat. Therefore without this moisture no man can live a moment. But also the cheife instruments of life are these spirits together with the native heat. Wherefore this radical moisture being dissipated and wasted, (which is the seat, fodder, and nourishment of the spirits and heat) how can they any longer subsist and remain? Therefore the consumption of the natural heat followeth the decay of this sweet and substance-making moisture, and consequently death, which happens by the dissipating and resolving of natural heat.

But since then these kind of Spirits with the natural heat, is contained in the substance of each similar part of our body (for otherwise it could not persist) it must necessarily follow, that there be as many kinds of fixed Spirits, as of similar parts. For because each part hath its proper temper and increase, it hath also its proper spirit, and also its own proper fixed and implanted heat, which heere hath its abode, as well as its original. Wherefore the spirit

and heat which is seated in the bone, is different from that, which is impact into the substance of a nerve, vein or such other similar part; because the temper of these parts is different, as also the mixture of the elements from which they first arose and sprung up. Neither is this contemplation of spirits of small account, for in these consist all the force and efficacy of our nature.

These being by any chance dissipated or wasted, we languish, neither is any health to be hoped for, the flour of life withering and decaying by little and little. Which thing ought to make us more diligent, to defend them against the continual effluxe of the threefold substance. For if they be decayed, there is left no proper indication of curing the disease, so that we are often constrained, all other care laid aside, to betake ourselves to the restoring and repairing the decayed powers. Which is done by meats of good juice, easie to be concocted and distributed, good wines and fragrant smells.

But sometimes these spirits are not dissipated, but driven in and returned to their fountains, and so both oppress and are oppressed; whereupon it happens we are often forced to dilate and spread them abroad by binding and rubbing the parts. Hitherto we have spoke of these things which are called natural, because we naturally consist of them; it remains that we now say somewhat of their adjuncts and associates by familiarity of condition.