402 A TEXTBOOK OF PHYSIOLOGY 



luria " where the oxalates are precipitated, but as a rule are not 

 increased, in the urine. Such patients generally suffer from an acid 

 dyspepsia, and have less acid sodium phosphate than usual in the 

 urine ; hence the oxalates fall out of solution. 



Hippuric Acid (C 9 H 9 X 4 3 ) occurs in human urine in small quantities 

 as sodium hippurate ( to gramme daily). It is much more plentiful 

 in the urine of herbivorous animals, such as the horse. It is increased 

 in man by the ingestion of fruits, such as mulberries and cranberries, 

 which contain aromatic acids which are oxidized to benzoic acid in 

 the body, and also by taking benzoic acid as a drug. Hippuric acid 

 is of interest, since its synthesis from benzoic acid and glycin takes 

 place by enzymic action in the kidney itself. If the kidney be perfused 

 with defibrinated blood containing these two bodies, hippuric acid is 

 formed. 



C 6 H 5 COOH+ CHoNHoCOOH = CH 2 NH.COC 6 H 5 .COOH + H.,0. 



Hippuric acid separates as crystals from the urine of the cow or 

 horse on standing after the addition of 125 grammes of ammonium 

 sulphate and 7-5 c.c. of concentrated sulphuric acid to 500 c.c. of urine. 

 The crystals, on evaporation with strong nitric acid, form nitro- 

 benzene, with the odour of oil of bitter almonds. 



Ammonia generally appears in small quantities in normal urine, 

 its amount varying according to the diet. When acids are introduced 

 into the body, or acid formation takes place in the organism, the 

 amount of ammonia in the urine is increased. The ammonia pro- 

 vided by the liver neutralizes the acids. This is sometimes the case 

 in diabetes mellitus and in eclampsia of pregnancy. 



Again, ammonia may be increased in the urine when the liver, 

 the chief seat of urea formation, is diseased. Normally, about 0-7 

 gramme of ammonia escapes conversion into urea. 



Chlorides. The chief chloride is that of sodium (1 gramme per 

 100 c.c. urine). It is derived chiefly from the " salt " of the food. 

 The presence of chlorides in urine may be shown by addition of silver 

 nitrate and nitric acid to the urine, when a white precipitate is obtained 

 which is soluble in ammonia. Without the addition of nitric acid, 

 the phosphates of the urine are also precipitated. 



To estimate the chlorides in the urine, they are precipitated by 

 excess of standard silver nitrate in presence of nitric acid. The excess 

 of silver nitrate is then found by titrating with a standard solution of 

 potassium or ammonium thiocyanate, using iron alum as the indicator 

 (Volhard's method). 



Chlorides are diminished in amount in the urine hi many febrile 

 affections, particularly pneumonia. 



Sulphates and Neutral Sulphur. Sulphur occurs in the urine in three 

 forms: (1) The inorganic sulphates; (2) the organic or ethereal sul- 

 phates; (3) neutral sulphur. 



Inorganic Sulphates occur as the compounds of sodium and potas- 

 sium. They are readily detected by adding a solution of barium 



