336 FUNCTIONS OF NUTRITION. 



a turbidity by coagulating the albumen. Alcohol, in equal volume, 

 will have the same effect ; and a solution of potassium ferrocyanide, 

 acidulated with acetic acid, will also produce coagulation. When all 

 these tests have been applied, no doubt will remain as to the presence 

 or absence of albumen. 



Deposits in the Urine. 



The deposits which appear spontaneously in the urine consist either : 

 1st, of some of its normal ingredients, thrown down in consequence of 

 a change in its composition ; or 2d, of exudations from the urinary 

 passages, owing to diseased local conditions. Those belonging to the 

 first class are the earthy phosphates and the urates. The most common 

 of those belonging to the second are blood, mucus, and pus. 



Deposits of the Earthy Phosphates. These deposits are always of a 

 white color, and are seldom abundant. When the urine is first passed, 

 they are disseminated through its mass in the form of a light cloudiness, 

 which settles slowly to the bottom of the vessel. The urine is alkaline 

 or neutral in reaction, and is usually of less than the average specific 

 gravity. The precipitate is amorphous, presenting no crystalline forms 

 under the microscope. It is at once redissolved on the addition of an 

 acid, and presents all the chemical reactions belonging to the earthy 

 phosphates. The alkaline condition of the urine, causing this deposit, 

 may be due to temporary diminution in the quantity of uric acid pro- 

 duced in the system, or to a formation of alkaline carbonates from the 

 use of fruits or vegetables containing salts of the vegetable acids. 



Deposits of the Uraies. The urates appear as a deposit when their 

 formation in the system is unusually abundant in proportion to the 

 urine, so that they are no longer held in solution. The urine is nearly 

 always concentrated, highly colored, above the average specific gravity, 

 and of a strongly acid reaction. The deposit is sometimes nearly white, 

 but usually of a light pink or even red color, according to the concen- 

 tration of the urine. If allowed to settle in a white porcelain vessel, 

 and the supernatant fluid poured off, the deposit is sometimes left as a 

 brick-red stain on the inner surface of the vessel, forming what is known 

 as the " brick-dust " sediment. 



Deposits of the urates are recognized by the two following characters. 

 First, they never appear while the urine is still warm, but only after it 

 has cooled ; the urine, when first passed, being always perfectly clear, 

 and becoming turbid on repose. Secondly, the urine, however turbid, 

 if heated in a test-tube, becomes again clear, usually before reaching the 

 boiling point. Both these characters depend on the solubility of the 

 urates at high temperatures. 



In rare cases, when urine is turbid with the urates and also contains 

 albumen, a double effect may be produced by the application of heat. 

 When the specimen is first heated, it clears up, owing to the solution 

 of the urates ; but, on approaching the boiling point, it again becomes 

 turbid from precipitation of the albumen 



