2. In Alkaline Urine.—(1) Phosphates.—While most common in alkaline urine, phosphates are sometimes deposited in neutral or feebly acid urines. The usual forms are: (a) Ammoniomagnesium phosphate crystals; (b) acid calcium phosphate crystals; and (c) amorphous phosphates. All are readily soluble in acetic acid.
(a) Ammoniomagnesium Phosphate Crystals.—They are the common "triple phosphate" crystals, which are generally easily recognized (Figs. 37 and [63], and [Plate IV]). They are colorless, except when bile-stained. Their usual form is some modification of the prism, with oblique ends. Most typical are the well-known "coffin-lid" and "hip-roof" forms. The long axis of the hip-roof crystal is often so shortened that it resembles the envelop crystal of calcium oxalate. It does not, however, have the same luster; this, and its solubility in acetic acid, will always prevent confusion.
| FIG. 37.—Various forms of triple-phosphate crystals (Ogden). |
When rapidly deposited, as by artificial precipitation, triple phosphate often takes feathery, star- or leaf-like forms. These gradually develop into the more common prisms. X-forms may be produced by partial solution of prisms.
(b) Acid Calcium Phosphate Crystals.—In feebly add, neutral, or feebly alkaline urines acid calcium phosphate, wrongly called "neutral calcium phosphate," is not infrequently deposited in the form of colorless prisms arranged in stars and rosets (Fig. 38, 1). The individual prisms are usually slender, with one beveled, wedge-like end, but are sometimes needle-like. They may sometimes take forms resembling tyrosin (Fig. 38, 2), calcium sulphate, or hippuric acid, but are readily distinguished by their solubility in acetic acid.
Calcium phosphate often forms large, thin, irregular, usually granular, colorless plates, which are easily recognized (Fig. 38, 3).
| FIG. 38.—Crystals of calcium phosphate: 1, Common form (copied from Rieder's Atlas); 2, needles resembling tyrosin (drawn from nature); 3, large, irregular plates (from nature). |
(c) Amorphous Phosphates.—The earthy phosphates are thrown out of solution in most alkaline and many neutral urines as a white, amorphous sediment, which may be mistaken for pus macroscopically. Under the microscope the sediment is seen to consist of numerous colorless granules, distinguished from amorphous urates by their color, their solubility in acetic acid, and the reaction of the urine.
The various phosphatic deposits frequently occur together. They are sometimes due to excessive excretion of phosphoric acid, but usually merely indicate that the urine has become, or is becoming, alkaline.
(2) Calcium carbonate may sometimes be mingled with the phosphate deposits, usually as amorphous granules, or, more rarely, as colorless spheres and dumb-bells, Fig. 39, which are soluble in acetic acid with gas-formation.