RENAL CALCULI 463 



Normal human urine contains oxalic acid in very small amounts. On 

 ordinary diet Fiirbiger found 20, Dunlop 17, Autenrieth and Barth 15 

 milligrams per day. This oxalic acid comes in part from the ingested 

 food. 



The resorption of oxalate in the digestive canal depends on the solu- 

 bility. The greater part of the oxalic acid of vegetables is in the form of 

 the insoluble calcium salt whose solubility is increased by the presence of 

 hydrochloric acid. The acidity of the gastric juice is doubtless of great 

 influence. According to an investigation by Dunlop,- Mohr and Salomon, 

 the excretion of oxalic acid in urine can be increased by feeding HC1 and 

 diminished by feeding alkalies. The amount of oxalic acid in urine, there- 

 fore, becomes with a vegetable diet very variable. But it is to be observed 

 that even when feeding a soluble oxalate, only a small portion is excreted 

 in the urine. G. Klemperer found that of 100 mg. oxalic acid 15 mg. were 

 excreted in the urine, 10 mg. in the feces, while the remainder was not to 

 be found and presumably was broken up in the intestine by bacteria. The 

 resorption of the soluble oxalate also depends on the amount of calcium 

 present at the same time. Consequently it does not seem strange that the 

 most contradictory findings are made concerning the resorption and ex- 

 cretion of the oxalic acid from the food. Abeles found that after eating 

 spinach containing 140 mg. of oxalic acid none appeared in the urine. 

 Lommel(ft) also found that after a diet rich in oxalic acid no more ap- 

 peared in the urine than with an oxalic acid free diet. Whether oxalic 

 acid is excreted by the intestines is not known. Pohl and Faust have 

 shown that injected oxalic acid appears in the urine and we may conclude 

 from these findings that resorbed oxalic acid is not broken down. 



To the oxalic acid of the food is added as a further exogenous source, 

 that which comes from the breaking up of other constituents of the food. 

 This portion arises in the same way as the oxalic acid which the organism 

 forms in its own metabolism and should therefore be reckoned with the 

 endogenous oxalic acid. 



Auerbach first established that dogs fed with meat and fat, i.e., oxalic 

 acid free food, excreted oxalic acid. W. Mills confirmed this result. 

 Afterwards Luthje(o-) observed that a fasting dog at the 12th to 16th day 

 still gave out an average of 9 mg. oxalic acid in the urine and that on a diet 

 consisting exclusively of milk and sugar. Human urine contained oxalic 

 acid on the llth day of this food. Mohr and Salomon found the same 

 thing. Oxalic acid is therefore proved to be a normal metabolism product 

 and the question arises from what does it come. 



The observation that in plants and in microorganisms oxalic acid is a 

 product of sugar led to the assumption that the carbohydrates are the 

 mother substance of oxalic acid in man and in other animals. It is now, 

 however, agreed that such a relationship does not exist. Fats also are no 



