EXCRETIONS 499 



amounts of benzoic acid or sodium benzoate would appear to be harmless. 

 Hippuric acid is found in the urine of herbivorous animals, such as the 

 horse and cow, in large amount, but only about 0.7 gram per day occurs 

 in human urine. Certain fruits and berries, cranberries in particular, 

 contain appreciable amounts of benzoic acid, while certain aromatic sub- 

 stances of vegetables are ultimately converted to benzoic acid. It may also 

 be formed by the putrefactive decomposition of the phenylamino acids in 

 the intestine. Benzoic acid or sodium benzoate is often used as a pre- 

 servative in canned fruit and catsup. All these factors contribute to the 

 hippuric acid output. It is stated that hippuric acid is decreased in fevers 

 and in certain kidney disorders where the synthetic activity of the renal 

 cells is diminished. 



Oxalic Acid. Oxalic acid in the form of calcium oxalate usually oc- 

 curs in the urine in very small amounts, about 0.02 gram in 24 hrs. Oxa- 

 lic acid is probably formed from the metabolism of proteins and fat. Its 

 output may be increased by the ingestion of foods which contain oxalic 

 acid. Such foods are cabbage, spinach, apples, grapes, etc. 



Aromatic Oxyacids and Derivatives. Under this heading may be men- 

 tioned phenol, p-cresol, indoxyl, scatoxyl, indol acetic acid and homogen- 

 tisic acid. These substances are all formed from the amino-acids, trypto- 

 phan, tyrosin and phenylalanin. Homogentisic acid is apparently formed 

 as a result of abnormal oxidation of the last two amino-acids men- 

 tioned. It occurs in alkaptonuria, a comparatively rare anomaly of metab- 

 olism. In this condition the excretion may amount to as much as 16 

 grams per day, although ordinarily it is less, i. e. } 3 to 5 grams. Intestinal 

 putrefaction (in rare instances, putrefaction elsewhere in the body) gives 

 rise to the formation of the other bodies mentioned. Phenol, />-cresol, and 

 indoxyl are eliminated in the urine partly in combination with sulphuric 

 acid, constituting the ethereal sulphates. Indoxyl-potassium-sulphate, or 

 indican, appears to depend upon the amount of intestinal putrefaction, 

 and to be an excellent index of it, but the same can hardly be said of the 

 ethereal sulphates as a whole, indicating that in part they have another 

 origin. Under normal conditions from 5 to 20 mg. of indican are excreted 

 per day, but in conditions showing excessive intestinal putrefaction as 

 much as 200 mg. may be eliminated. In certain of these cases indol acetic 

 acid is excreted, giving rise to the so-called urorosein reaction. According 

 to the recent studies of Folin and Denis the larger part of the phenols 

 (phenol, p-cresol, etc.) are excreted in the free form. The daily elimina- 

 tion of phenols appears to average about 300 mg., of which about 60 per 

 cent is free and 40 per cent conjugated. 



Sugar. Sugar appears to be present in normal urine in very small 

 amounts. As a result of the recent studies of Benedict, this subject has 

 attracted considerable interest, Normal urine apparently contains from 

 0.02 to 0.2 per cent of sugar with an average of about 0.07 per cent. Of 



