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tion, that no Disease requires copious bleeding so much as the Ophthalmia.

OPHTHALMICS, Medicines proper for Diseases of the Eyes; as Ophthalmic Waters, Ophthalmic Powders, Ointments, &c. See EYES.

There is an excellent Ophthalmic prepared of Sugar of Saturn.

The fifth Pair of Nerves of the Brain, dividing into three Branches; the firft is call'd Ophthalmic, because it goes to the Eye: This again fubdivides into two Branches, after fending out feveral Twigs which encompass the Optic Nerves, and are diftributed in the Choroides. See NERVE. OPHTHALMOGRAPHIA, that Branch of Anatomy which confiders the Structure and Compofition of the Eye; the Ufe of its Parts, and the principal Effects of Vifion. Sec EYE. Our Countryman, Dr. William Briggs, has publiſhed an excellent Opbibalmographia, and Plempius another. The Word is form'd from the Greek οφθαλμος, Eye; and γραφη, Defcription. OPHTHALMOSCOPIA, that Branch of Phyfiognomy which confiders a Perfon's Eyes; to deduce thence the Knowledge of his Temperament, Humour, and Manners. See PHYSIOGNOMY. OPIATE, in Medicine, any Compofition wherein Opium is an Ingredient. Sce OPIUM. The Word is frequently alfo apply'd to Confections, Anti- dotes, and Eleétuaries; the fome fay 'tis only properly applicable to foft Compofitions: In which fenfe it is de- fined an internal Remedy, varioufly compofed of Powders, Pulps, Liquors, Sugar, or Honey, reduced into a foft Con- fillence. See CONFECTION, ELECTUARY, &c. The Opiate of Solomon is a Compofition of great Fame, fo call'd from one Solomon, a Phyfician, its Inventor; and first published by Laurence Forbert. There are a particular kind of Opiates, call'd Incarnatives, for the Teeth and Gums, made of Alum, Sumach, Lig- num Aloes, Myrrh, Mattic, &c. reduced into Powder. OPIATES is alſo uſed in the general for all Medicines given with an Intention to procure Sleep; in which fenfe the Word is of the fame Import with Narcotics, Hypnotics, Soporifics, and Pacifics. See SLEEP, NARCOTIC, HYP- NOTIC, &c. The Operation of Opiates, or the manner wherein they produce their Effect in the Body, Dr. Quincy thus lays down: All Pain is a Stimulus on the Part affected, and is at- tended with Contractions of the pained Membranes, which occafion a greater Afflux than ordinary of the nervous Juice that way: On the other hand, Pleaſure, or a delightful Senfation in any part, is accompanied with a ſmooth Undu- lation, and eafy Reflux of the nervous Juice towards the Brain. This is, as it were, the Entertainment of the Mind; with which being taken up, it doth not determine the Spirits to the Organs of Motion: that is, there is fuch a Relaxa- tion of the mufcular Fibres, and fuch a Diſpoſition of the nervous Fluid, as is neceffary to Sleep. See PAIN, &c. Now, 'tis fhewn that an agreeable Senfation produced in the Stomach, together with a diftention of its Membranes, is the immediate Caufe of that Sleepinefs, to which we are inclinable after Eating; the one engaging the Mind, the other acting on the Body. For Pleafure amufes the Soul, and the Fulness of the Veffels in the Brain, checks and hinders, in fome meafure, the derivation of the nervous Juice into the Organs. Now, to apply this; a moderate Dofe of an Opiate, ufually tranfports People with a pleafing Senfation, to that degree, that, as they often exprefs themselves, they are in Heaven; and tho they do not always fleep, (which pro- ceeds from the prefentation of pleafing Images to the Mind fo ftrongly, that, like Dreams, they do over-engage the Fancy, and fo interrupt the State of Reft) yet they enjoy fo perfect an Indolence and Quiet, that no Happiness in the World can furpafs the Charms of fo agreeable an Extafy. Thus we have from thefe Medicines, but in a far more eminent degree, all thofe Effects which are obferred to follow upon that grateful Senfe in the Stomach, which a moderate Fulness produceth. For no Bodies are fo fit and able pleafingly to affect our fenfible Membranes, as thofe which confift of volatile Parts, whofe Activity is tempered and allay'd by the Smoothness of fome which are lubricating and oily; for they lightly rarify the Juices of the Stomach, and caufe a pleasant Titillation of its nervous Coat, whereby there is induced an agreeable Plenitude, and the Mind is entertained with Ideas of Satisfaction and Delight. OPI Opiates are found to abate immoderate Secretions and Evacuations, which they do by removing that Irritation of the Organs, whereby they are occafion'd. And herein lies the incraffating Quality of thofe Medicines, in that the twitching Scnfe upon the Membranes of the Lungs, Bowels, &c. being leffen'd, the sharp Humour is fuffer'd to lodge there in a greater Quantity, before it is fo troubleſome as to be thrown off and expell'd; it being all one as if there were no Irritation of the Part, if the uneafy Senfe thereof be not regarded by the Mind. And these Effects will all be heightned by the Mixture of the Opiate Particles with the Blood; which is hereupon rarify'd, and diftends its Veffels, eſpecially those of the Brain; and this does still, to a greater degree, leffen the Influx of the nervous Fluid to the Parts, by preffing upon the Tubuli, or little Canals, through which it is derived. Whence the reafon of that Difficulty of breathing, which Opiates occafion; this Symptom being in- feparable from the Rarefaction of the Blood in the Lungs. OPINION, a probable Belief; or a doubtful, and un- certain Judgment of the Mind. See BELIEF. And thus, we easily fee upon what Mechaniſm the other Virtues of Opiates depend; for their eafing Pains, checking Evacuations, &c. proceed not only from the Mind's being taken up with a pleafing Senfe, whereby it is diverted from a difagreeable one; but all Pain being attended with a Contraction of the Part, the Relaxation of the Fibres, which they caufe, eludes and deftroys the Force of the Stimulus. Opi ion may be ftrictly defined the Affent of the Mind to Propofitions not evidently true at firſt fight; nor deduced, by neceffary Confequence, from others that are fo; but fuch as carry the Face of Truth. See TRUTH, and ERBOR, alfo FAITH, &c.

The Schools define it, Affensus Intellectus cum formidine de opposito; An Affent of the Understanding, with some fear or distruft on the contrary part. Thus the Logicians say, that Demonstrat on begets Science, or Knowledge; and probable Arguments beget Opinion. See KNOWLEDGE and PROBABILITY.

Wherever the Mind's Acquiescence in a Truth proposed to it, is accompanied with any Doubt, this is what we call an Opinion. See DOUBTING.

Plato makes Opinion a Medium between Knowledge and Ignorance; clearer and more express than Ignorance; yet more obscure and unsatisfying than Knowledge. See IGNORANCE.

OPISTHOTONOS, in Medicine, a kind of Convulsion, wherein the Body is bent backwards, so as to form, as it were, a Bow; in which sense the Word is used in opposition to Emprosibotonos, wherein the Body is sent forwards. See CONVULSION.

The Opistbotonos arises from a tonic Motion of the Muſcles of the posterior Parts of the Body; especially those on the back of the Head.

The Word is compounded of the Greek οπισω, backward, behind, and τεινειν, tendere, to ſtretch, bend. OPIUM, in Pharmacy, &c. a Juice drawn from the Head of the black Poppy, and afterwards inspissated. See POPPY.

When the Juice flows of itself, thro' Incisions made in the Poppy Heads, it is properly call'd Opium; when drawn by Expression, it assumes the Name of Meconium. See MECONIUM.

The difference between the Qualities and Virtues of the two Juices, is very considerable: The former is preferable on all accounts; but it is exceeding rare; the Turks, among whom it is produced, and who make great use of it, never allowing it to be exported: so that it is the latter that is ordinarily uſed among us, and fold for Opium.

"Tis moftly brought from the Levant and Cairo; generally very impure; the Levantines, to shorten their Labour, and to have the more Juice, drawing it equally from the Heads and the Leaves of Poppies, by Expression, and then reducing it to the thickness of an Extract by Fire.

It must be chosen dry, the smoothest, and blackest possible, of a drowsy smell, and neither rugged, nor sticky, nor all in a Mass.

"Tis a popular Error, that there is any such thing as white Opium; for tho' the Juice as it runs from the Heads of the Poppies be of a Milk-colour, it always becomes of a very deep brown as it thickens. Wherever it is found yellowish or soft, 'tis a sign the Juice has not had Fire enough.

Prepared Opium is call'd Laudanum; of which there are two Kinds: the one, Simple; extracted by means of Rain- Water, and Spirit of Wine: The other Compound, call'd Laudanum Opiatum; wherein there enter several other Ingredients. See LAUDANUM.

The Uses of Opium are to sooth Pain, to excite Sleep, to stop Vomiting and Loosenesses. Its Dose is from half a Grain to two Grains. Some Persons, who have much habituated themselves to it, can take 50 or 60 Grains. Charas says, he has taken 12 Grains himself; and adds, he knew one who made no scruple of 36. And in the Philos. Trans. we have an instance of one Mrs. Lovelock, who, in a Fever, in three days time, took 102 Grains.

It raises the Spirits, occasions agreeable Sensations, and has much the same effect with Wine or strong Spirits. The

Turks ordinarily take to the quantity of a Drachm when