228 ORGANIC AGRICULTURAL CHEMISTRY 



accurate determination of total nitrogen in urine is a corn- 

 plicated chemical process, the former is used very largely as 

 a clinical method for judging the protein metabolism of 

 the body. This also will be considered in the experiment 

 study. 



Uric Acid. — This compound, closely related to urea in its 

 constitution (seep. 102), is an important constituent in man and 

 other flesh-eating animals, though present in quite small amounts. 

 The daily excretion is about 0.6 grams under normal conditions, 

 and represents about i.o per cent of the total urine nitrogen. 

 The amount varies greatly however under certain pathological 

 conditions. The source of uric acid is the metabolism of a 

 special group of proteins, viz. the nudeo-proteins, and in 

 mammals is one of the minor products of metabolism. In 

 birds, however, it is the chief nitrogenous metabolic product, 

 being formed similarly to urea in mammals. 



Creatinine. — This nitrogen compound is present in urine to 

 the amount of about 1.5 grams per day, equivalent to about 3.6 

 per cent of the total urine nitrogen. It is an anhydride of 

 creatine which is a normal constituent of muscular tissue. 

 Creatine is related to urea through guanidine which is imino 

 urea or 



/NH2 



HN =c<; 



Ammonia. — About 3.0 per cent of the total nitrogen in 

 urine is present as ammonia. The amount is, however, sub- 

 ject to considerable variation, depending upon the relative 

 amounts of acid and basic constituents of the food. If not 

 held by acids in a stable form, it is converted into urea. The 

 relative amounts of these two constituents are thus inter- 

 dependent and in pathological cases have been known to be 

 almost reversed. According to Sherman the amounts of the 

 different nitrogen compounds in urine per day following a 

 high protein diet are as follows ; 



