But amongst many others, I met with none more observable than this [Schem. 5.]
Fig. X. pretty Shell (described in the Figure X. of the fifth Scheme) which, though as it was light on by chance, deserv’d to have been omitted (I being unable to direct any one to find the like) yet for its rarity was it not inconsiderable, especially upon the account of the information it may afford us. For by it we have a very good instance of the curiosity of Nature in another kind of Animals which are remov’d, by reason of their minuteness, beyond the reach of our eyes, so that as there are several sorts of Insects, as Mites, and others, so small as not yet to have had any names; (some of which I shall afterwards describe) and small Fishes, as Leeches in Vinegar; and smal vegetables, as Moss, and Rose-Leave-plants; and small Mushroms, as mould: so are there, it seems, small Shel-fish likewise, Nature shewing her curiosity in every Tribe of Animals, Vegetables, and Minerals.

I was trying several small and single Magnifying Glasses, and casually viewing a parcel of white Sand, when I perceiv’d one of the grains exactly shap’d and wreath’d like a Shell, but endeavouring to distinguish it with my naked eye, it was so very small, that I was fain again to make use of the Glass to find it; then, whilest I thus look’d on it, with a Pin I separated all the rest of the granules of Sand, and found it afterwards to appear to the naked eye an exceeding small white spot, no bigger than the point of a Pin. Afterwards I view’d it every way with a better Microscope and found it on both sides, and edge-ways, to resemble the Shell of a small Water-Snail with a flat spiral Shell: it had twelve wreathings, a, b, c, d, e, &c. all very proportionably growing one less than another toward the middle or center of the Shell, where there was a very small round white spot. I could not certainly discover whether the Shell were hollow or not, but it seem’d fill’d with somewhat, and ’tis probable that it might be petrify’d as other larger Shels often are, such as are mention’d in the seventeenth Observation.

Observ. [XII]. Of Gravel in Urine.

I Have often observ’d the Sand or Gravel of Urine, which seems to be a tartareous substance, generated out of a saline and a terrestrial substance crystalliz’d together, in the form of Tartar, sometimes sticking to the sides of the Urinal, but for the most part sinking to the bottom, and there lying in the form of coorse common Sand; these, through the Microscope, appear to be a company of small bodies, partly transparent and partly opacous, some White, some Yellow, some Red, others of more brown and duskie colours.

The Figure of them is for the most part flat, in the manner of Slats or such like plated Stones, that is, each of them seem to be made up of several other thinner Plates, much like Muscovie Glass, or English Sparr to the last of which, the white plated Gravel seems most likely; for they seem not onely plated like that, but their sides shap’d also into Rhombs, Rhomboeids, and sometimes into Rectangles and Squares. Their bigness and Figure may be [Schem. 7.]
Fig. 2. seen in the second Figure of the seventh Plate, which represents about a dozen of them lying upon a plate ABCD, some of which, as a, b, c, d seem’d more regular than the rest, and e, which was a small one, sticking on the top of another, was a perfect Rhomboeid on the top, and had four Rectangular sides.

The line E which was the measure of the Microscope, is ¹⁄₃₂ part of an English Inch, so that the greatest bredth of any of them, exceeded not ¹⁄₁₂₈ part of an Inch.

Putting these into several liquors, I found oyl of Vitriol, Spirit of Urine, and several other Saline menstruums to dissolve them; and the first of these in less than a minute without Ebullition, Water, and several other liquors, had no sudden operation upon them. This I mention, because those liquors that dissolve them, first make them very white, not vitiating, but rather rectifying their Figure, and thereby make them afford a very pretty object for the Microscope.

How great an advantage it would be to such as are troubled with the Stone, to find some menstruum might dissolve them without hurting the Bladder, is easily imagin’d, since some injections made of such bodies might likewise dissolve the stone, which seems much of the same nature.

It may therefore, perhaps, be worthy some Physicians enquiry, whether there may not be something mixt with the Urine in which the Gravel or Stone lies, which may again make it dissolve it, the first of which seems by it’s regular Figures to have been sometimes Crystalliz’d out of it. For whether this Crystallization be made in the manner as Alum, Peter, &c. are crystallized out of a cooling liquor, in which, by boyling they have been dissolv’d; or whether it be made in the manner of Tartarum Vitriolatum, that is, by the Coalition of an acid and a Sulphureous substance, it seems not impossible, but that the liquor it lies in, may be again made a dissolvent of it. But leaving these inquiries to Physicians or Chymists, to whom it does more properly belong, I shall proceed.