URINE AND ITS CONSTITUENTS. 723 



Tests for pyrocatechin. 



1 . Add dilute ferric chloride solution : a green color is evolved. 

 Add a little tartaric acid and then ammonia : the green color changes 

 to violet, but on acidifying with acetic acid the green color reappears. 



2. Add sodium hydroxide : the solution turns green, brown, and 

 black. 



3. Add lead acetate : pyrocatechin is precipitated as a lead com- 

 pound. 



4. Show that Fehling's solution and ammonio-silver nitrate solu- 

 tion are reduced by pyrocatechin, but that it does not act on alkaline 

 bismuth solution. 



Sodium, potassium, calcium, and magnesium occur in the urine 

 mainly as inorganic salts. They are derived from the food. The 

 amount present is not important clinically. 



Oxalic acid. The source of this acid in urine is unknown. Many 

 vegetables and fruits contain oxalates, which, after ingestion, are 

 secreted to a great extent unchanged. That oxalic acid occurs as a 

 metabolic product is shown by its excretion during starvation, and 

 also when the diet is exclusively protein and fat. It is believed that 

 the protein, and not the fat, is concerned here. An increased elimi- 

 nation of oxalic acid occurs in diabetes, icterus, and in the condition 

 called oxaluria. 



Enzymes in urine. Pepsin has been shown to be present in small 

 amount in normal urine ; lipase and a diastase have been found in a 

 few cases. 



Pathological constituents. While the normal constituents of 

 urine, and especially the quantity excreted in twenty-four hours, 

 give valuable information in regard to the whole process of metab- 

 olism taking place in the body, pathological constituents often show 

 with great precision abnormal conditions existing in the body, and 

 the qualitative or quantitative determination of pathological con- 

 stituents is therefore a valuable aid in diagnosing disease. Of patho- 

 logical constituents are of chief interest the proteins (albumin, globu- 

 lin, albumoses, peptones), sugars, and the constituents of blood or 

 bile. But many other substances occur at times, and should not 

 be overlooked in the examination. To these substances belong 

 acetone, diacetic acid, melanin, a compound giving the diazo-reac- 

 tion, etc. 



