CH. XXXVII.] URINAKY DEPOSITS 567 



(NH 4 MgP0 4 + 6H 2 0). This crystallises in "coffin-lid " crystals (see 

 fig. 431) or feathery stars. 



(2) Stellar phosphate, or calcium phosphate ; this crystallises in 

 star-like clusters of prisms. 



As a rule normal urine gives no precipitate when it is boiled ; 

 but sometimes neutral, alkaline, and occasionally faintly acid urines 

 give a precipitate of calcium phosphate when boiled : this precipitate 

 is amorphous, and is liable to be mistaken for albumin. It may be 

 distinguished readily from albumin, as it is soluble in a few drops of 

 acetic acid, whereas coagulated proteid does not dissolve. 



The phosphoric acid in the urine chiefly originates from the phos- 

 phates of the food, but is partly a decomposition product of the phos- 

 phorised organic materials in the body, such as lecithin and nuclein. 

 The amount of P 2 5 in the twenty-four hours' urine varies from 2*5 

 to 3 '5 grammes, of which the earthy phosphates contain about half 

 (1 to 1-5 gr.). 



Tests for the Inorganic Salts of Urine. 



Chlorides. Acidulate with nitric acid and add silver nitrate ; a white precipitate 

 of silver chloride, soluble in ammonia, is produced. The object of acidulating with 

 nitric acid is to prevent phosphates being precipitated by the silver nitrate. 



Sulphates. Acidulate with hydrochloric acid, and add barium chloride. A 

 white precipitate of barium sulphate is produced. Hydrochloric acid is again added 

 first, to prevent precipitation of phosphates. 



Phosphates. i. Add ammonia; a white crystalline precipitate of earthy (that 

 is, calcium and magnesium) phosphates is produced. This becomes more apparent 

 on standing. The alkaline (that is, sodium and potassium) phosphates remain in 

 solution, ii. Mix another portion of urine with half its volume of nitric acid ; add 

 ammonium molybdate, and boil. A yellow crystalline precipitate falls. This test is 

 given by both classes of phosphates. 



Quantitative estimation of the salts is accomplished by the use of solutions of 

 standard strength, which are run into the urine till the formation of a precipitate 

 ceases. The standards are made of silver nitrate, barium chloride, and uranium 

 nitrate or acetate for chlorides, sulphates and phosphates respectively. 



Urinary Deposits. 



The different substances that may occur in urinary deposits are 

 formed elements and chemical substances. 



The formed or anatomical elements may consist of blood 

 corpuscles, pus, mucus, epithelium cells, spermatozoa, casts of the 

 urinary tubules, fungi, and entozoa. All of these, with the exception 

 of a small quantity of mucus, which forms a flocculent cloud in the 

 urine, are pathological, and the microscope is chiefly employed in 

 their detection. 



The chemical substances are uric acid, urates, calcium oxalate, 

 calcium carbonate, and phosphates. Barer forms are leucine, tyrosine, 

 xan thine, and cystin. We shall, however, here only consider the 

 commoner deposits, and for their identification the microscope and 

 chemical tests must both be employed. 



