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There are, moreover, those who cherish a spirit of scepticism, from an idea that it denotes the exercise of a superior intellect; it must be admitted, that at that period in the history of Europe, when reason first began to throw off the yoke of authority, it required superiority of understanding as well as intrepidity of conduct, to resist the powers of that superstition which had so long held it in captivity; but in the present age, observes Mr. Dugald Stewart, “unlimited scepticism is as much the child of imbecility as implicit credulity.” “He who at the end of the eighteenth century,” says Rousseau, “has brought himself to abandon all his early principles, without discrimination, would probably have been a bigot in the days of the league.”

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He who is governed by preconceived opinions, may be compared to a spectator who views the surrounding objects through coloured glasses, each assuming a tinge similar to that of the glass employed; thus have crowds of inert and insignificant drugs been indebted to an ephemeral popularity, from the prevalence of a false theory; the celebrated hypothesis of Galen respecting the virtues and operation of medicines, may serve as an example; it is a web of philosophical fiction, which was never surpassed in absurdity. He conceives that the properties of all medicines are derived from what he calls their elementary or cardinal qualities, Heat, Cold, Moisture, and Dryness. Each of these qualities is again sub-divided into four degrees, and a plant or medicine, according to his notion, is cold or hot, in the first, second, third, or fourth gradation; if the disease be hot, or cold in any of these four stages, a medicine possessed of a contrary quality, and in the same proportionate degree of elementary heat or cold, must be prescribed. Saltness, bitterness, and acridness depend, in his idea, upon the relative degrees of heat and dryness in different bodies. It will be easily seen how a belief in such an hypothesis must have multiplied the list of inert articles in the materia medica, and have corrupted the practice of physic. The variety of seeds derived its origin from this source, and until lately, medical writers, in the true jargon of Galen, spoke of the four greater and lesser hot and cold seeds; and in the London Dispensatory of 1721, we find the powders of hot and cold precious stones, and those of the hot and cold compound powders of pearl. Several of the ancient combinations of opium, with various aromatics, are also indebted to Galen for their origin, and to the blind influence of his authority for their existence and lasting reputation. Galen asserted that opium was cold in the fourth degree, and must therefore require some corresponding hot medicine to moderate its frigidity.^[37]