It is impoffible, or extremely difficult, to perceive, even with the beft Microscopes, the differences of the fmall Pores of Plants, and the internal filtrations of their Juices; and though one could diftinguifh fomething herein, yet would it be extremely difficult to divine the particular proprieties which must be produced by these differences.

The colours of Flowers, Fruits, &c. cannot give any indication of thefe Proprieties; for the Flowers of Nappel and Aconite are blue, as well as thofe of Buglofs and Succory. There are Apples and Pears which have a bad Taste, though they have most lively and moft beautiful Colours. There are poifonous Fruits which have colours like thofe of Cherries and Apricocks; and though the Milkthiftle has in it a white Juice as well as the Lettice, there is notwithstanding a very great difference in their Proprieties.

The indications which may be drawn from Odours are also extremely uncertain. There is a Species of Mushrooms which please the smell and yet are poifonous: The Apples of the Mandragora have an agreeable Odour enough, tho' moft pernicious Qualities. Among feveral Melons which have equally an agreeable Smell, fome have an excellent Tafte, and others are flat and infipid.

Rosemary, Myrtle, Lavender, Wormwood, &c. which have odoriferous Leaves, throw out, in the beginning of their refpective Diftillations, an Oil which the Chymifts call Effential, whence we may conjecture that their odour proceeds from their oily and inflamable parts; but the odoriferous Flowers, as the Rofe, Jonquile and Pink, accord not at all with this Hypothefis.

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If we rub between our Fingers the Leaves of Baum, they grow more odoriferous, as if their ugly and fulphureous parts, which are lefs volatile than watery Vapours, stood in need of being chafed to facilitate their evaporation; but the Leaves of a Rofe being thus rubbed lofe their fmell.

The Musk Cranebill does not fmell till after Sun-fet, and it is difficult to give any other Reafon for it, than that its Odour is produced by fome very fubtle and light Particles, which rife all alone without any mixture of watery Vapours, though the Plant be not heated.

The Flowers of Myrtle and Wormwood throw out armoniac Spirits in the beginning of their diftillations; whereas the greatest part of odoriferous Flowers yield only acid.

Frankincense burnt is of a grateful Odour; burnt Rofes and Wine caft into the Fire, give ftinking Vapours.

From which Experiments it is eafy to conclude, that good or bad Odours proceed fometimes from the mixture of two or three particu lar Principles, and at other times from the mixture of two or three others; but that these different Combinations cannot be well known, and though they were, they would not make us know the unions or feparations of the other Principles which are the principal virtues of Plants.

Savours may also easily deceive us.

Amongst bitter Herbs fome are poisonous, others wholesome; there are fome that are equally infipid which have qualities extremely different; neither can we certainly tell what are the Principles which conftitute favours, and confequently we cannot found upon the Taste and

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certain knowledge of the particular virtues of Plants, and of their different proprieties.

Nor can they be any more known by the operations of Chymiftry; for we fhall find a great many nourishing Plants, which in their diftillations yield Salts, Oils, Spirits, &c. alike in taste, fmell, and other effects with thofe given by Hemlock and Tithymalles.

Arum which takes one by the Throat, and Water-pepper which is fo very biting upon the Tongue, yield fixed and volatile Salts, and Spirits, and Oils very near like thofe of Lettice and Purflain which are almoft infipid.

Wine and Darnel intoxicate, which neither Wheat nor Sugar will do, though we may draw a burning Spirit from thefe Matters as well as from Wine and Darnel.

Shall we fay that Plants which abound with a light and armoniac Spirit will heat? And that thofe which have a great deal of acid Spirit cool? That fuch whofe fixed Salt refembles common Salt, because it does not trouble diffolved fublimate, will have other virtues than those whofe Salts are drawn from the Lees of burnt Wine, which we call Salt of Tartar? But all thefe Conjectures are deceitful, for Succory, Lettice, and feveral other Herbs which are cooling, discover not any acid, but a great deal of light or armoniack Spirit. The Nettle does the fame thing, though it be apparently very different from Lettices and Succories.

Young growing Plants yield none, or a very fmall quantity of acid Spirit, but a great deal of armoniack, even in the beginning of their diftillation; but being come to their maturity, and ready to dry, they yield a great deal of acid, and but a very little armoniack Spirit,unless at the end

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of their diftillation; and yet we generally make no diftinction between the virtues which they have being young, and those which they have when adult.

The extract of Galls mingled with Eggs in a Difh, coagulates them, and makes them look as if they were boiled; Spirit of Wine does the fame thing, and thefe Matters drefs them as foon as if the Dish was put upon a fufficient Fire; Sal Armoniack and Salt of Tartar have contrary Effects to thofe of Galls and Spirit of Wine, for they hinder the Blood from coagulating, if when newly drawn from the Veins, we mingle with it Water wherein thefe Salts are diffolved; and we cannot say that in Galls and in Spirit of Wine there is no Sal Armoniack, or lixivial Salt; whence it is evident that diftillations cannot give us any knowledge of thefe imperceptible. mixtures and unions, any more than make us judge and determine what accident it is which makes rotten Wood luminous; or why Ox dung does not heat, and that of Horfes and Sheep, which live on the fame Grafs, actually does.

If we find a difference in the Salts of fome Plants after diftillation, this may proceed becaufe fome do not retain by an exact union fome other Principles which the Fire could not feparate, or that the Fire even made new unions; and thus the Fire may take away a noxious quality from one Plant, and give the like to another, which had nothing of it before; for fince their virtues proceed from the different unions and mixtures of fome Principles, and Chymistry introduces new unions and feparations, it may draw Poifon from a falutary Plant, and a good Medicine from a poisonous one; but it will never make us know what caufes their goodnefs or malignity in their

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natural State, and we shall of neceffity be obliged to wait a long while before we fhall be able to bring about this Discovery. We We may also say that Plants, fuch as they are in their natural State, will rather make us acquainted with their virtues, than when they are changed by diftillation, and we may prove it by the following. Reafons.

The Principles of Plants being mixed in the Earth, and each of them finding there its corrective, we do not obferve therein any odour or favour, or scarce any virtue falutary or hurtful; and the decoctions of common Earths will do no manner of harm to those who fhall drink of them; but the particular difpofition of each Plant diverfly ranging thefe Principles, caufes to appear in the Flowers, Bloffoms, and Fruits of certain Plants, most beautiful and moft lively Colours, exquifite favours, agreeable odours, and in other Plants ill Scents, Bitterness, &c. which fignal diverfity makes them to be eafily diftinguished from one another, and fometimes give us Conjectures good enough to know their goodness or malignity; whereas the action of Fire confounds all these things, and it is alfo difficult to difcern by the Senfes from what Plants proceed the Waters, Oils, and other Matters drawn from them by distillation.

We may likewife doubt whether fome of the most active Principles of Plants, as those which cause Poifon, or ferve for the cure of Diftempers, do not evaporate by the great heat of the Furnace through the Retorts and bolt-heads of Glafs, fince we observe that the virtue of mineral Waters is loft or diminished in a few days by being carried from one place to another, though the Veffels which contain them are fealed up