Analysis, conducted with care, leads us, however, to form some conjecture of the nature of the vegetable. The expressed juices of the green and watery plants (the oleraceae) are slightly laxative and cooling; in the language of the Boerhaavians, aperient; of the cruciform plants (the tetradynamiae of Linnaeus,) antiscorbutic. Bitter extracts are tonic, often anthelmintic; oils and mucilages demulcent; essential oils generally-stimulant and carminative; and resins either purgative or diuretic. Whatever opinion, however, be formed of the advantages of analysis in investigating the nature of plants, it has certainly assisted the pharmaceutical treatment of vegetable remedies, and, in the animal kingdom, has been of the greatest utility in showing the fallacy of many boasted remedies, from the identity of their nature, or their insolubility. Even musk and castor we find nearly approaching in their nature to resins, and the gluten of vegetables to animal substances. In the mineral kingdom, our obligations to chemistry are too numerous for repetition, and too obvious to detain us. We shall only remark, among these, the antidotes discovered to some of the most active poisons, and the advantages we derive from our power of preparing artificial mineral waters.

The utility of natural history in investigating the properties of medicines is very considerable. To be able to acertain with certainty the identity of any plant is an object of no little importance, as it prevents our disappointment in future trials. Were it not for the assistance of natural history, the greater part of the experience of the ancients would have been useless; and were it not for the aid of Caspar Bauhine, we should wander through their works, like the first travellers in the American forests. All around would be unknown: we could neither appreciate their views, nor follow their examples; yet we have known commentators on the ancient authors, who, supposing they meant some given medicine, were little anxious what it might be. A deep knowledge of botany, however, is unnecessary. We now know more than 50,000 species, and of these scarcely a hundred are employed in general practice; and of the latter, two-thirds, or even a greater proportion, are useless. Yet the principles of the science should be known, for the reasons just mentioned; and, above all, the foundation of the natural orders for the reasons and purposes already assigned. (See Botany.) One great advantage is, that if a given plant cannot be procured, a similar one may be selected from its natural order; and the author of the little tract on botanical analogy has shown, in a variety of entertaining examples, how the same remedy has been extolled and forgotten; repeatedly, at different periods, and under different names, revived.

Observation and experience are, on the whole, the safest guides; but here again we are lost in wildernesses or fogs. Numerous remedies, recommended as certain, are found to fail: what we have ourselves, at different times, considered to be firmly established as proofs of holy writ, at others we have found less substantial than the shadow of a shade. In every step we feel the truth of the Hippocratic axiom "experientia fallax." If those whose education and experience contribute to point out the danger of deception, find that the post hoc is not always equivalent to the propter hoc. how many sources of deception must surround those not accustomed to such observations ? Yet medicines are commended by men of the first character, rank, and abilities, as certain remedies; every newspaper teems with affidavits, and we are deemed incredulous indeed it wc disbelieve a bishop or a judge. Medical evidence differs greatly from every other: we are obliged to act on the result of reasoning often extremely insufficient; our decisions on the effects of medicines, on the contrary, require the most rigorous examination. If a man asserts, for instance, that he has been cured of a consumption by Godbold's syrup, it implies several positions extremely doubtful. How can he ascertain that the disease was a consumption? for in this respect the most judicious practitioner is often deceived. But, admitting that it is so, we know that vomicae are often completely discharged: we know that an ulcer spontaneously heals, and it is as probable that diet and regimen may have effected the cure, as a medicine equally inconsiderable in its powers. If then we cannot trust to experience, what must be our resource? Though nothing may be certain in the operation of medicines, and our evidence only establish different degrees of probability, yet a rigorous scrutiny in the investigation of every fact respecting this part of the science will greatly facilitate our progress in similar circumstances. Authors on the materia medica abound with assertions respecting the properties and use of every medicine, and the most inert is often represented in colours too glaring for even the most active. This partly arises from the want of discrimination just mentioned, but more often from an anxiety to display the extent of their own learning; and such are the accumulated recommendations which the student finds, that he thinks his only labour a selection. So frequent are his disappointments, that he at last mistrusts even the most respectable authorities. Who will cleanse this Augaean stable? It will require an Herculean hand; and the little that can be done in a general work like this can scarcely lessen the labour. We not, however, mispend our time, if we examine shortly the conduct of the best authors on this subject.

In this enumeration we should have omitted the systems of the astrologers and the signaturists, but that the fancies of the latter still remain. The former we may safely neglect, though not wholly forgotten by the empirical old women of the country, who still prefer collecting plants at the full or new moon. The signaturist prefers plants which resemble the part diseased; and euphrasia is still used for complaints of the eyes, though its original claim to notice arose from a black spot in its corolla resembling the pupil; and the pulmonaria is employed in diseases of the lungs, because its form, its texture, and its spotted areolae, afford a distant resemblance to these organs. Crollius is the great authority of this sect: but to return to more rational authors.