It is only necessary to add a few further remarks, in order to shew in what particular complaints chalybeates, even in their most perfect state, are pernicious. By this means many of the diseased will be guarded against a fatal error: and as the prejudice in favour of such applications is so universally prevalent, it is hoped a few pages allotted to this subject will be deemed a most essential service to a deluded community. By removing such a pernicious partiality, the health, if not the lives of thousands, may be saved, to the great enjoyment of themselves and their relatives. Dr. Knight says very justly, "that the explication of the manner of the operation of chalybeate medicines in human bodies is grounded upon false principles, and not matters of fact; to wit, that all chalybeate preparations, in a liquid form, owe their medicinal efficacy to the metal dissolved, whether in an aqueous or spirituous menstruum, retaining its metallic texture." To avoid entering into the whole detail of this interesting argument, it is only here stated in support of the above assertion, that as mineral waters are impregnated with a combination of sulphurs, salts, and earth, their virtues cannot be properly ascribed, as they have been, to the metals which they contain. It might be further proved, that iron cannot possibly enter the blood, retaining its essential qualities; for metals in general, except mercury, are suspended in liquids in _solutis principiis_, or principles disengaged, which are thus deprived of their metallic properties. Iron, entering the body as a volatile vitriolic acid, cannot act by its specific gravity as mercury does; it therefore acts _per accidens_, and not _per se_. But admitting that waters, however impregnated with iron, are efficacious in checking all diarrhoea and other profuse evacuations, by closing the relaxed vessels, and incrassating the fluids, yet as they prove sometimes so astringent as to stop the natural secretions, the consequences are frequently cramps, dangerous convulsions, which often end in fevers, inflammations, and mortifications, their indiscriminate use should be most cautiously avoided. Chalybeates, thus contracting the least pervious glands, should not be taken in acute inflammations, or in any complaints that are attended with a quick and strong pulse, a plethora, or extravasation of humours. They are equally dangerous in all nervous contractions, or where the blood is got into the arteriolae, or capillary vessels. Thus, instead of acting like the sanative tea, which softens, smoothes, and unbends the two constringed fibres, the vitriolic salts of this mineral water but more contract the fibrillae, by operating like so many wedges, which ultimately tear, rend, or divide the tender filaments. It must, however, be admitted that mineral waters are very beneficial in cachexies, scurvies, jaundice, hypochondriacal and hysterical affections. Having paid this