Where nervous Fibres and Blood Vessels concur to the Constitution of the Organ, the Tumor is ever accompanied with a painful Inflammation. Such being the Operation of prepared Mercury, it is capable of disordering the Animal Œconomy in many Ways, according to the Functions of the affected Parts. A complete Examination of them would swell these Sheets beyond the proposed Size; I therefore reserve it for the Subject of a future Publication. Here I confine myself to the Effects of Mercurial Salts on the Organs of Vision, in Order to account for the Phænomena of the Disease about which I am treating. Mercurial Particles, carried into the minute Vessels of the ocular Muscles, irritate them: Irritation is soon followed by Contraction and Obstruction; thus the whole Substance of the Muscles becomes inflamed, and their Bulk swelled. Hence from the inward Pression, Stiffness and obtuse Pain, which are felt in this Disease. That the Light’s Rays, which fall on the Eye, may express a distinct Image on the[20] Choroïdes, they are to have their Focus thereon. This cannot be effected, except when this Membrane is at a certain Distance from the Lens; and this Distance is ever relative to the Position of Objects. Rays reflected by proximate Objects, being less refrangible, have their Focus more distant from the Lens, than Rays reflected by remote ones. In order to distinguish Objects at various Distances, the Soul therefore approaches the Choroïdes to, or remove it from, the Crystaline; that is to say, the Soul alters the Figure of the Eye:--An Alteration ever effected by the Motions of ocular Muscles. Thus, when the Motion of these Muscles is obstructed by their swelling, it is plain that there is no being able to see clearly Objects at several Distances. When viewing remote Objects, the Eye is retracted towards the Bottom of the Orbit by the Contraction of its strait Muscles; for as they contract, these Muscles bring back the anterior Hemisphere of the Globe (to which their Apponevroses are adhering) to the posterior one; they thereby approach the Choroïdes to the Crystaline. Thus the strait Muscles of the Eye being swelled and contracted by irritating Mercurial Particles, Objects cannot be distinguished but at one particular Distance.[21] When viewing near Objects, the Eye, laterally compressed by its oblique Muscles, seems to be forced out of the Orbit. Its Globe being thereby lengthened, the Choroïdes is more distant from the Crystaline. But as the Eye has only two oblique Muscles to four strait ones, when its Muscles are all swelled to the same Degree, the Choroïdes is more retracted towards the Crystaline by the former, than it is retracted from by the latter. Thus near situated Objects cannot be so clearly distinguished as the remote.