AM Of N'T AND COMPOSITION OF THE URINE 563 



within the body. The amount of ammonia in the urine, therefore, is a 

 measure of the acid bodies of the blood. For the latter reason the deter- 

 mination of the ammonia excretion in urine is of some clinical importance. 

 The ingestion of mineral acids increases the ammonia excretion, while 

 alkalies tend to reduce it. During: fasting and in diseases such as 

 diabetes, where there is an abnormal metabolism, the amount of ammonia 

 in the urine is increased. Ordinarily the daily output of ammonia nitro- 

 gen does not exceed 0.5-0.6 gm., constituting 3-5 per cent of the total 

 amount of nitrogen. According to Nash 20 and Benedict the formation 

 of the urinary ammonia occurs in the kidneys. Thus, there is more am- 

 monia in the blood of the renal vein than in that of the systemic circula- 

 tion, and the latter does not become increased by intravenous injection 

 of acid. That the kidney produces ammonia is further shown by the fact 

 that this decrease* in the blood after complete nephrectomy. 



Creatinine. On a meat-free diet the daily excretion of creatinine is 

 remarkably constant, amounting to from^T to 11 nig. per kilogram of 

 body weight. For this reason its determination is accepted as an in- 

 dispensable feature in metabolism investigations involving urine analy- 

 sis. Any gross variation from the normal amount indicates the certain 

 failure of the attendants to collect all of the twenty-four-hour specimen 

 of urine. 



The creatinine is one of the last of the urinary constituents to accumu- 

 late in the blood during renal insufficiency, and for this reason affords 

 a reliable prognostic indication concerning the patients' condition. A 

 rise in the creatinine concentration of the blood is evidence of serious 

 renal disease, patients with concentrations of 5 mg. never recovering 

 (Chase and Myers). 7 The concentration of creatinine in the urine is 

 about 100 times greater than in the blood, in which there is 1-2 mg. per 

 100 c.c. 



In adult man creatine does not appear in the urine save during starva- 

 tion or wasting diseases. In woman it is absent save after postpartum 

 resolution of the uterus. Children commonly excrete creatine along 

 with creatinine until the middle years of childhood. 



The Purine Bodies and Uric Acid. The most important purine in 

 human urine is uric acid. Xanthine is the next in importance, and small 

 amounts of hypoxanthine, guanine, and adenine are found. 



The human body has the almost unique distinction among mammals 

 of not being able to destroy any of the uric acid it produces, and hence 

 all the uric acid formed during metabolism must be excreted in the urine. 

 Unfortunately the kidney appears to be less competent to rid the body 

 of this waste than it is of the other urinary metabolites, and one of the 



