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PLATE XI.

OXALATE OF LIME.

Oxalate of lime seldom forms a granular deposit, which sinks to the bottom of the vessel, but usually the crystals are buoyed up by the small quantity of mucus which the Urine contains. In removing a portion of the deposit, therefore, it is desirable not to plunge the pipette quite to the bottom of the glass.

Deposits consisting of octohedra increase very much after the Urine has been passed. Some specimens which have been allowed to stand for twenty-four hours or longer deposit an abundant sediment, consisting of large crystals, while the Urine may have been quite destitute of crystals immediately after it was passed. I have never observed this in the case of the dumb-bell crystals, which, there is reason to believe, are formed in the kidney, and probably undergo no further change.

Crystals of oxalate of lime may be preserved as permanent objects in creosote fluid. Glycerine and Canada balsam refract so highly that the crystals are hardly visible when mounted in these media.

The form of the crystal is that of a flattened octohedron, with one axis much shorter than the other two; and the different appearances produced by the position in which the crystal is placed are so peculiar, that some observers have mistaken these for distinct forms of crystals. The most important characters are represented in fig. 1, and these were copied from a glass model made to resemble the crystal itself. The figures have been compared with real crystals of large size, which were made to rotate in the field of the microscope, by moving very slightly the thin glass covering the preparation.

PLATE XI.

OXALATE OF LIME.-OXALURATE OF LIME.

Fig. 1. a, b, c, d, e.-Appearances of the same crystal of oxalate of lime viewed in different positions. The crystal is supposed to be seen first lying upon one of its broad surfaces, and then gradually rotated from the observer until one edge is opposite to the eye.

f, g, h.-The same crystal seen sideways, one of the lateral angles being towards the eye.

i. An octohedral crystal mounted as a dry object.
k.—Unusual form of compound crystal of oxalate of

lime.

Fig. 2.-Dumb-bell crystals, and allied forms of oxalurate of lime.

a to f.-Circular and oval forms.

g to m.- Crystals approximating in form to the dumb-bell.

n to s.-Regular and irregular crystals.

t to w.-Perfect dumb-bell crystals. The three first figures subjected to the prolonged action of acetic acid.

t.-A crystal which had been allowed to soak for several weeks in strong acetic acid. The crystalline material is almost entirely dissolved away, leaving the organic matter in the form of a cell-wall. In u the action has not extended so far. In v the action of the acid is very slight; and in w a crystal is represented in its ordinary state,

Fig. 3. Large dumb-bell crystals, from the Urine of a child two years old, suffering from jaundice. These crystals were perfectly symmetrical.

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