A Faculty is a certain power, and efficient cause, proceeding from the temperament of the part, and the performer of some actions of the body. There are three principal Faculties governing mans body as long as it enjoys its integrity: the Animal, Vitall and Natural.

The Animal is seated in the proper temperament of the Brain, from whence it is distributed by the Nerves into all parts of the body which have sense and motion. This is of three kinds, for one is moving, another sensitive; the third principal. The sensitive consists in the five external senses, sight, hearing, taste, smell and touch. The Moving principally remains in the Muscles and nerves, as the fit instruments of voluntary motion. The principal comprehends  the Reasoning faculty, the Memory and Fantasie. Galen would have the Common or inward sense to be comprehended within the compass of the Fantasie, although Artistotle distinguishes between them.

The Vitall abides in the Hart, from whence heat and life is distributed by the Arteries to the whole body: this is principally hindered in the diseases of the Breast; as the Principal is, when any disease assails the Brain; the prime action of the vital faculty is pulsation, and that continued agitation of the Heart and Arteries, which is of threefold use to the body: for by the dilatation of the Heart and Arteries the vital spirit is cherished by the benefit of the Aire which is drawn in; by the contraction thereof the vapors of it are purged and sent forth, and the native heat of the whole body is tempered by them both.

The last is the Natural faculty which has chosen its principal seat in the Liver, it spreads or carries the nourishment over the whole body; but it is distinguished into 3. other faculties; the Generative which serves for the generation and forming of the Issue in the womb; the Growing or increasing faculty which flourishes from the time the Issue is formed, until the perfect growth of the solid parts into their full dimensions of Length, height and breadth. The nourishing faculty which as servant to both the other repairs and repays the continual effluxe, and waste of the three-fold substance; for Nutrition is nothing else but a replenishing, or repairing whatsoever is wasted or emptied. This nourishing faculty endures from that time the Infant is formed in the womb until the end of life. 

It is a matter of great consequence in Physicke to know the 4 other faculties, which as servants attend upon the nourishing faculty; which are the Attractive, Retentive, Digestive, and Expulsive faculty.

1. The Attractive draws that juice which is fit to nourish the body, that I say which by application may be assimilated to the part. This is that faculty which in such as are hungry draws down the meat scarce chawed, and the drink scarce tasted, into the gnawing and empty stomach.   
2. The rententive faculty is that which retaines the nourishment once attracted untill it be fully laboured and perfected concocted; and by that meanes it yeels no small assistance to the digestive faculty. For the naturall heat cannot performe the office of concoction, unlesse the meat be embraced by the part, and make some stay therein. For otherwise the meat carryed into the stomacke never acquires the forme of Chylus, unlesse it stay detained in the wrincles thereof, as in a rough passage, untill the full time of Chylification. 
3. The Digestive faculty assimulates the nourishment, being attracted and detained into the substance of part whose faculty it is, by the force of the inbred heate and proper disposition or temper of the part. So the stomacke plainely changes all things which are eat and drunke into Chylus, & the liver turnes into Chylus into blood. But the Bones & Nerves convert the red and liquid blood which is brought down unto them by the capillary or small veins, into a white and solid substance. Such concoction is far more laborious in a Bone and nerve, than in the Musculous flesh. For the blood being not much different from its nature, by a light change and concretion turnes into flesh. But this Concoction will never satisfie the desire of Nature and the parts, unlesse the nourishment purged from its excrements, put away the filth and drosse, which must never enter into the substance of the part. 
4. Wherefore there do not onely two sorts of excrements remaine of the first and second Concoction, the one thicke, the other thin, as we have said before; but also from the third Concoction which is performed in every part. The one of which we conceive onely by reason, being that which vanisheth into Aire by insensible Transpiration. The other is knowne sometimes by sweats, sometimes by a thicke fatty substance stayning the shirt; sometimes by the generation of haire and nailes, whose matter is from fuliginous and earthly excrements of the third Concoction. Wherefore the fourth Faculty was necessary which might yeeld no small helpe to nourishment: 

It is called the Expulsive, appointed to expell those superfluous excrements which by no action of heate, can obtaine the forme of the part. Such faculties serving for nutrition are in some parts two-fold; as some common, the benefit of which redounds to the whole body, as in the ventricle, liver & veines; Others onely attending the service of those parts in which they remaine, and in some parts all these 4. as well common as proper, are abiding and resident, as in those parts we now mentioned: some with the 4. proper have onely two comon, as the Gall, Spleene, Kidneies and Bladder. Others are content onely with the proper, as the simular and Musculous parts, who if they want any of these 4. faculties, their health is decayed either by want of nourishment, an ulcer, or otherwise. The like unnatural affects happen by the deficiency of just and laudable nourishment. But if it happen those faculties do rightly performe their duty, the nourishment is changed into the proper substance of the part, and is truly assimulated, as by these degrees. First it must flow to the part, then by joyned to it, then agglutinated, and lastly as we have said, assimulated. Now we must speake of the Actions which arise from the faculties.