OXALIC ACID, HIPPURIC ACID. 



dogs after being fed with uric acid excrete much calcium oxalate. It should, how- 

 ever, be pointed out that the oxalic acid may also result as an oxidation-product 

 from derivatives of the fatty-acid series. Oxalic acid is formed from oxaluric acid 

 by the taking up of water, together with the appearance of urea. 



Oxalic acid is wanting on a pure milk-diet. Almost all vegetable articles 

 of food contain it. The ingestion of substances that contain a considerable amount 

 of calcium oxalate, such as sorrel and tea, increases the excretion. Citric acid, 

 treated with ozone, yields carbon dioxid and oxalic acid. The presence of calcium 

 oxalate after the use of lemons is thus explained. Increased elimination of oxalic 

 acid in the urine is designated oxaluria, and is considered in part a sign of retarded 

 metabolism, as, for instance, from deficiency of oxygen, in the dog; and in part 



as dependent upon hyperacid- 

 ity of the gastric juice. It may 

 become dangerous in conse- 

 quence of the formation of cal- 

 culi. In conjunction with oxa- 

 luria, the uric acid has often 

 been found increased. The 

 amount of oxalic acid is in- 

 creased in the urine of jaun- 

 diced persons. According to 

 Neubauer, dissolved calcium 

 oxalate, held in solution by 

 acid sodium phosphate, also 

 occurs in the urine. The elim- 

 ination of this substance takes 

 place in crystalline form the 

 more completely, the more 

 nearly the urine approaches a 

 neutral reaction. 



Hippuric acid, C 9 H 9 NO 3 , 

 benzoylamidoacetic acid, oc- 

 curs in the urine of herbivora, 

 and as the principal represen- 

 tative of the nitrogenous prod- 

 ucts of metabolism; and in 

 human urine only in small 

 amount from 0.3 to 3.8 grams 



in a day. It is an odorless, monobasic acid, with a bitter taste, crystallizing in color- 

 less four-sided prisms; and it is readily soluble in alcohol, but only in 600 parts of 

 water. It is a conjugate acid and results in the body from benzoic acid (or from 

 the cuticular substance of plants, which is closely related to it) , or from oil of bitter 

 almonds, cinnamic acid, quinic acid (in hay), which are readily transformed by 

 reduction (quinic acid) or by oxidation (cinnamic acid) into benzoic acid, with 

 which glycin combines with the giving up of water. 



C 7 H 6 O 2 + C 2 H 5 NO 2 = C 9 H 9 NO 3 + H 2 O 



Benzoic Acid Glycin Hippuric Acid Water. 



The formation of hippuric acid is, accordingly, dependent principally upon 

 the food. It is, therefore, wanting in the urine of nursing calves, as well as after 

 the ingestion of such vegetables as possess no cuticula; as, for instance, earthy 

 bulbs and peeled vegetables. Similar syntheses of glycin occur in the organism 

 also after ingestion of many other substances, as, for instance, after administration 

 of substituted benzoic acids or of aromatic acids. As the albuminates also are 

 capable of yielding benzoic acid and oil of bitter almonds through oxidizing agents, 

 the hippuric acid may be formed in the body from disintegrating albuminates. 

 This explains the fact that it is found also in the urine of fasting persons. 



In the dog, the conjugation of hippuric acid takes place in the kidneys; in 

 frogs, also outside these organs. Kuhne and Hallwachs refer the formation to 

 the liver, Jaarsfeld and Stokvis to the kidney, the liver and the intestines. The 

 observation of Salomon that hippuric acid was present in the blood and in the 

 liver of nephrectomized rabbits after injection of benzoic acid into the blood 

 indicates that the formation does not take place exclusively in the kidneys. Fur- 

 ther, the hippuric acid formed in human beings may, under pathological condi- 

 tions, particularly when the reaction is alkaline and albuminuria is present, be 

 again decomposed in the urine, in consequence of a fermentative process. Whether 



FIG. 149. Kreatinin-zinc Chlorid: a, spherical aggregations with 

 radiate striation; b, groups after crystallization out of water; c, 

 less common form from alcoholic extract. 



