Practical physiological chemistry : a book designed for use in courses in practical physiological chemistry in schools of medicine and of science . peridin. It alsoresponds to the murexid test (see page 249) and to Schiffsreactiqn (see page 249). Urates.—The urate sediment may consist of a mixtureof the urates of ammonium, calcium, magnesium, potassiumand sodium. The ammonium urate may occur in neutral,alkaline or acid urine, whereas the other forms of urates areconfined to the sediments of acid urines. Sodium urateoccurs in sediments more abundantly than the other urates. 324 PHYSIOLOGICAL CH

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Practical physiological chemistry : a book designed for use in courses in practical physiological chemistry in schools of medicine and of science . peridin. It alsoresponds to the murexid test (see page 249) and to Schiffsreactiqn (see page 249). Urates.—The urate sediment may consist of a mixtureof the urates of ammonium, calcium, magnesium, potassiumand sodium. The ammonium urate may occur in neutral, alkaline or acid urine, whereas the other forms of urates areconfined to the sediments of acid urines. Sodium urateoccurs in sediments more abundantly than the other urates. 324 PHYSIOLOGICAL CHEMISTRY, The urates of calcium, magnesium and potassium are amor-phous in character, whereas the urate of ammonium is crystal-line. Sodium urate may be either amorphous or crystalline.When crystalline it forms groups of fan-shaped clusters orcolorless, prismatic needles (Fig. 102, below). Ammoniumurate is ordinarily present in the sediment in the burr-likeform of the thorn-apple crystal, i. e., yellow or reddish-brown spheres, covered with sharp spicules or prisms (PlateVI, opposite page 324). The urates are all soluble in hydro- FlG. 102.. Acid Sodium Urate. chloric acid or acetic acid and their acid solutions yield crystalsof uric acid upon standing. They also respond to the murexidtest. The clinical significance of urate sediments is very simi-lar to that of uric acid. A considerable sediment of amor-phous urates does not necessarily indicate a high uric acidcontent, but ordinarily signifies a concentrated urine havinga very strong acidity. Cystin.—Cystin is one of the rarer of the crystalline uri-nary sediments. It has been claimed that it occurs moreoften in the urine of men than of women. Cystin crystal-lizes in the form of thin, colorless, hexagonal plates (Fig. 32, PLATE VI.