Page:Cyclopaedia, Chambers - Volume 2.djvu/535

 PUR

PUPILLA, Pupil, n Anatomy, a little Aperture, in the '"luoie oi me Uvea, and Ins of the Eye j thro' which the A *u_\suf Light pals to the Cryftalline, in order to be painted on the Retina, and caufe Vu.on. See Eye and Vision. 'Tis obiervcd, that as we are fotced to ufe various A-
 * rtures to our Optic Glaffcs; fo Nature has made a like

'rovilion in the Eyes of Animals, whereby to /hut out too much, and admit fufficient Light; by the Changes in the Aperture of the Pupil. Sec Telescope.

t

( 912 ) PUR

The "Purgation of Mercury is performed by paflini. it thro a Chamois Skin. SeeMEReuRY.

Gold \spurged by the Coppcl, Cementation, Mfe See Gold, Coppel, £fc.

The Purgations of other Metals are perform'd by repeated Furious, £sc. s *» M ,. ~ . - c^-

See Metal, iSc,

Purgation, Catharfis, in Medicine, is an excretory

Motion, arifing from a quick and orderly Contraftion of the

flefhy Fibres of the Stomach, and Interlines; whereby the

1 he Siruclure ot the Uvea ana Iris is luch, as that by their Chyle, corrupted Humours, and Excrements lods'd therein

Aperture, the Pupil, is contradable and dilatable at plea- are protruded further and further; and at length quite ex'

fure; fo as to accommodate itfelf to Objects, and to ad mit more or fewer Rays, as the Object being more vivid and near, or more obfeure and remote, requires more or lefs Light It being a constant Law, that the more lu- minous the Object, the fmaller the 'pupil; and again, the nearer the Object, the fmaller the Pupil j and vice verfi. See Uvea and Ray.

This Alteration ot the Pupil is effected by certain Mufcu- lar Fibres on the Outride of the Uvea; which are form'd of Nerves detach \t hither from the Sclerotica — Thefe Fi- bres proceeding, ftraighr, from their Origin towards the Centre, terminate in the Orbicular Limb or Verge of the Pupil, which confi. is of Orbicular Mufcles j whereby the

Figure and Space of the Pupil are defined. The firft, or

longitudinal Fibres, dilate the Aperture of the Pupillai the latter, or orbicular ones, conftringe it.

Some Authors, however, attribute the Motions of the Pupilla to the Ligamentum Ciliare; and others think, that

both this, and the fibres of the Uvea, concur herein

Wu.Derham adds, that while the Pupil opens, and fhuts; the Ligamentum Ciliare dilates, or compreffes the Cryflal- line, and brings it nigher to, or further from the Retina, as the Object is mure or lefs remote. See Ciliare, &c.

The Figure of the Pupil in various Animals, is wonder- fully adapted to their various Circumftances and Occafions. In fome, e. gr. in Man, 'tis round; that Form being fit- teft, for the petition of our Eyes, and the various ufe we make of them in all Directions.

In others, 'tis elliptic or oblong; in fome of which, e.gr. the Horfe, Sheep, Ox, l£c. the Ellipfis is tranfverfe, and the Fifltire large, to enable them to fee laterally and even with a little Light; and thereby both to gather their Food the better in the Kiehr, and to avoidDangers on either fide — In others, e.gr. the Car, the Ellipfis is erect; and alfo capa- ble ot opening very wide and fhu. ting very clofe; by means of the latter of which, that Animal can exclude all, but, as it were, a tingle Ray of Light, and fo avoid all the In- conveniences of the bright Sun; and by the former can take in all the fainted Rays, and thus avoid the Inconve- niences of the Night. An incomparable Provision for thefe Animals, which are to watch and way-lay their Prey both by Day and Night; to fee upwards and downwards; to climb, SSc. See Eye.

FUP1LLAR1TY, the State of a Pupil; in oppofition to Puberty. See Puberty.

Hence, alfo, Pupil comes to be ufed, by way of Exten- sion, in Univerfities, <£c. in the fenfe of Alutnnus, for a Youth under the Education, or Difcipline of any one.

PUREECK Stone, fee Stone.

PURCHASE, in Law, the Acquisition of Goods, viz. Lands, Tenements, $$c. by means of Money; in contra- diftinction to thofedefcending from Anceflors. See Goods.

Purchase, in the Sea-Language, has the fame Signifi- cation with draw, at Land.— Thus, they fay the Capftan purchafes a-pace, i. e. draws in the Cable a-pace : And when they cannot draw or hale any thing in with the Tackle, they fay, the Jackie will not purchafe.

PURE, fomething free of any admixture of foreign or heterogeneous Matters. See Purification.

Hence Pur a Eleemofyna, Pure Alms, a Tenure whereby the Churchmen hold Lan<is in Scotland, fomewhat on the footing of the primitive Clergy. See Tithes.

¥v re Hyperbola, in Geometry, is an Hyperbola without »ny Oval, Node, .Spike, or Conjugate Point. See Curve.

Pure Mathematics, fee Mathematics.

FURFLEW, a Term in Heraldry, expreffing Ermines, Peans, or any of the Furs, when they compofe a Bordure rounda Coat of Arms. SeePEAN, Bordure, tfc.

--, .-ngth quite ex- cluded the Body. See Excretion, Stomach, Intes- tines, l$c.

Purgations one of the principal Species of Evacuat ion. See Evacuation.

For the Means and Manner wherein it is effetled, fee Purgative.

Purgation, in Law, is the clearing one's felf of aCrime whereof he is accufed before a Judge. See Try al.

Of thefe Purgations there was antiently much ufe in England; cfpecially touching Matters of Felony charged on Clerks; and they are ftill retained in the Ecdefiaftical Court, in fufpicion of Incontinently, i$c.

fttrgntitm is either Canonical, or Vulgar.

Canonical is that prefcribed in the Canon- Law; the Form whereof, now obtaining, is, that the Party /hall take his Oath he is clear of the Fact obje3ed; and bring fo many ot his honeft Neighbours, not above twelve, as the Court fhall affign him, to fwear, on their Confciences, they be- lieve he fwears truly.

The Vulgar, and mod antient Manner, was by Fire, or Water, or Combat; ufed by Infidels, and by Chriftians too, till abolifhed by the Canon Law. See Ordeal, Wa- ter, Combat, i5c.

Combat, tho' now difufed, may yet be flill praflifed by the Laws of the Realm, in Cafes where Evidence is want- ing, and the Defendant ratherchufes Combat than any other Trial. SeeSuTHDURE, Duel, Champion, i£c.

Purgation, in Tragedy, a Term which Arillotle ufes for rhe Effect of Tragedy on the Mind.

That Fhilofopher obferves, rhat Tragedy, by means of the Terror and Companion which it excites, purges thofe Paffions out of the Soul.

Indeed, Corneille adds, that Tragedy frequently makes thofe Paffions, inftead of purging 'em; fo that he takes Arijlotle's Purgation to be no more than a Chimtera. See Tragedy.

Menfirual Purgations, the Catamema or Menfes of Women. See Menses.

PURGATIVE, or Purging Medicine, a Medicament which evacuates the Impurities of the Body by Stool 5 call'd alfo a Cathartic. See Stool, Purgation and Cathartic.

Purgatives are divided, with regard to their Effect, into Gentle, Moderate, and Violent.

Gentle Purgatives are fuch as operate very mildly; as tamarinds, CaJJia, Manna, Rhubarb, Senna, and moft of the Mineral Waters. See Cassia, Manna, Rhubarb tie. '

The Moderate purge fomewhat more briskly, as Jalap, Scammony, &c. See Jalap and Scammony.

The Violent operate exceffively; as Coloquintida, Helle- bore, Laureola, &c. SeeCoLocjuiNTiDA, Hellebore, £=?c.

Purgatives are, again, divided with regard to the Hu- mour they evacuate, into Phlegmagogues, Cholagogues, Me- lanogogues, and Hydrogogues; each whereof fee under its proper Article Phlegmagogue, Cholagogue, i£c.

The modern Phyficians reject this Divifion; andihewthe Operations of all Purgatives to be alike.

theory of the Operation of Purgatives.

Purgatives make one of the moft important Articles in Medicine— Their Effect is produced by vellicating and irritating the nervous Fibres of the Stomach and Inteffines 5 and thereby urging 'em to an Expulfion. See Stomach and Intestine.

An Idea of the Manner of their Operation is thus given

Thus they fay, He beareth Gules, a Bordure Purflew, us by Dr. Cheyne. Ve J?,; ^Si'IS, ' h c" '^ B °,- rt! ure! s Ve ."y-. A Purgative Medicine being received into the Stomach,

by the Mouth, its Particles do there vellicare or ftimulate.

PURGATION, the Aft o( purging, fcowering, or puri- fying a thing, by feparating and cartying off any Impurities found therein. See Purification.

Purgation, in Pharmacy, is a cleanfing of a Medicine by retrenching its Superfluities; as the Wood and Seeds out of Caffia, Stones out of Dates Tamarinds and other Fruits.

Purgation is alfo ufed in Chymiftry for feveral Prepa- rations of Metals, and Minerals; to clear 'em of their Im- purities : more ufually call'd Purification. See P«r. ifi.

VATION.

the Fibres of the Stomach, and thereby increafe rhedigeftive Faculty, i. e. bring the mufcular Fibres of rhe Stomach and the Mufcles of the Abdomen and Diaphragma into more frequent Contractions than ordinary; till the Medicine is admitted into the Inteffines, the Fibres and Glands where- of being more fenfible than thofe of the Stomach, (whofe Parts by the frequent, rough Contacts of one againlt ano- ther, and of the grofs Bodies often thrown into it, are as it were, deadned) it eafily moves and brings "'em into frequent, forcible ContraSions, whereby thefe Glands are

fqueez'd*