And Chrystallography. This subject can scarcely be considered as a medical one, since, perhaps, the deposition of bony matter, more certainly calculous concretions, are the only instances of crystallization in the human body. Yet, as chemistry has made such gradual and effectual encroachments on medicine, and as the variety of crystals are often mentioned in these pages, a short account of this subject is, in every view, necessary and proper.

Linnaeus, who made, very early, some imperfect and ineffectual attempts to arrange minerals from their external appearances, spoke of the more obvious and common forms, which salts and other bodies assume, when passing from a state of fluidity to that of a solid. The chemical mineralogists, who, under the guidance of Cron-stedt, succeeded, turned the attention of philosophers from the obvious properties to the component parts; when, in 1772, the first edition of Rome de I Isle's Chrystallography appeared; and the second edition, in five volumes, was published in 1783. About this period Bergman, in a separate dissertation, greatly illustrated the subject. Since that time, the attention of mineralogists was again directed to external forms, by the abbe Haiiy; who, in numerous papers, published in the Journal des Mines, and afterwards, in 1801, in a separate work, in four volumes octavo, explained, with mathematical accuracy, all the different forms of crystals; taught us the mode of their construction, by a successive application of molecules; and pointed out the way in which the primitive chrystal may be detected. The form of the crystals, in a great variety of solids, has thus been traced; and so constant is the crystallization of the same ingredients', that, in more than one instance, the crystallographer has instructed the chemist; in general, his fiat has confirmed the chemical analysis. Chrysun, (from gold). An epithet of two collyria for the eyes, and also of two pessaries for the uterus, in .AEtius.