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A TEXTBOOK OF PHYSIOLOGY 



Indoxyl is formed from indol (C 8 H 7 N) and probably in the intest inal 

 wall during absorption. Indol is formed as the result of bacterial 

 action upon tryptophane. 



The best test for indican is to add to the urine some concentrated 

 HC1 containing a trace of ferric chloride. Upon shaking with a little 

 chloroform, indigo blue, or occasionally indigo red, is formed. 

 Normal urine gives but a trace of colour, if any ; with excess of 

 indican the colour is deep. 



Phosphates. These are grouped as (1) alkaline phosphates of 

 potassium, sodium, and ammonium; (2) earthy phosphates of calcium 

 and magnesium. The two groups occur in about the ratio of 3 : 1. 

 Phosphoric acid forms three series of salts: Normal phosphate, 

 Na 3 P0 4 ,Ca 3 (P0 4 ) 2 ; mono-hydrogen phosphate, Na 2 HP0 4 ,Ca 2 H(P0 4 ); 

 di-hydrogen phosphate, NaH 2 P0 4 ,CaH.,(P0 4 ) 2 . The normal and 



FIG. 225. CALCIUM CARBONATE (FROM HUMAN URINE), x 400. 



mono-hydrogen phosphates are alkaline to litmus, the di-hydrogen 

 to acid. The three sodium phosphates and the di-hydrogen calcium 

 phosphate are soluble in water, the other two calcium salts are in- 

 soluble. The deposit of phosphates which sometimes occurs is due 

 to the earthy phosphates being precipitated when the urine loses its 

 acid reaction. When CO 2 is driven from urine by heating, such a 

 deposit of phosphates sometimes occurs. It is distinguished from a 

 coagulum of protein by the fact that it is readily soluble in acetic 

 acid. 



The earthy phosphates yield a white crystalline precipitate on the 

 addition of ammonia. The presence of phosphates generally may be 

 shown by adding nitric acid and ammonium molybdate to urine. 

 Upon heating this, a yellow precipitate is obtained. 



To estimate phosphates in the urine, some acid sodium acetate 

 is first added to the urine to prevent the formation of free nitric acid 



