| FIG. 39.—Indistinct crystalline sediment (dumb-bell crystals) of calcium carbonate. Similar crystals are formed by calcium oxalate and calcium sulphate (after Funke). |
(3) Ammonium Urate Crystals.—This is the only urate deposited in alkaline urine. It forms opaque yellow crystals, usually in the form of spheres (Plate IV, and [Fig. 63]), which are often covered with fine or coarse spicules, "thorn-apple crystals." Sometimes dumb-bells, compact sheaves of fine needles, and irregular rhizome forms are seen (Fig. 40). Upon addition of acetic acid they dissolve, and rhombic plates of uric acid appear.
| FIG. 40.—Crystals of ammonium urate (one-half of the forms copied from Rieder's Atlas, the others from nature). |
| PLATE IV |
| Sediment of alkaline fermentation (after Hofmann and Ultzmann). |
These crystals occur only when ammonia is present in excess. They are generally found along with the phosphates in decomposing urine and have no clinical significance.
B. ORGANIZED SEDIMENTS
The principal organized structures in urinary sediments are: tube-casts; epithelial cells; pus-corpuscles; red blood-corpuscles; spermatozoa; bacteria; and animal parasites. They are much more important than the unorganized sediments just considered.
1. Tube-casts.—These interesting structures are albuminous molds of the uriniferous tubules. Their presence in the urine probably always indicates some pathologic change in the kidney, although this change may be very slight or transitory. Large numbers may be present in temporary irritations and congestions. They do not in themselves, therefore, imply organic disease of the kidney. They probably occur only in urine which contains, or has recently contained, albumin.
While it is not possible to draw a sharp dividing-line between the different varieties, casts may be classified as: (1) Hyaline casts; (2) waxy casts; (3) granular casts; (4) fatty casts; (5) casts containing organized structures—(a) epithelial casts; (b) blood-casts; (c) pus-casts; (d) bacterial casts. As will be seen, practically all varieties are modifications of the hyaline.