AMOUNT, COMPOSITION, AND CHARACTER OF URINE 529 



of the blood. For the latter reason the determination 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 in- 

 creased. Ordinarily the daily output of ammonia nitrogen does not 

 exceed 0.5-0.6 gm., constituting 3-5 per cent of the total amount of 

 nitrogen. 



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

 remarkably constant, amounting to from 7 to 11 mg. per kilogram of 

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

 dispensable feature in metabolism investigations involving urine an- 

 alysis. 



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. Normally the blood contains from 1 to 2 mg. per 100 c.c. 



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 Meyers) 7 The concentration of creatinine in the urine is 

 about 100 times greater than in the blood. 



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. Among the 

 most interesting of the salts of the urine to the clinician are the urates, 

 because an accumulation of uric acid in the body was believed to be 

 responsible for many obscure clinical conditions. It is quite true that 

 the salts of uric acid are found in higher than normal amount in some 

 diseases, especially gout, leukemia, and chronic nephritis, but the many 

 vague theories associated with uric acid and disease have long ago been 

 exploded. 



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 



