394 PHYSIOLOGICAL CHEMISTRY 



the aUantoin will reduce the solution. Compare with the result on uric acid, 

 page 381. 



AMINO -ACIDS 1 



Certain of these acids are always present in normal urine. The 

 excretion of total amino-acid nitrogen by a normal adult averages 

 0.4-1.0 gram per day or about 2-6 per cent of the total nitrogen. 

 Free amino-acid nitrogen (see van Slyke procedure, Chapter IV) is 

 considerably less than this, and ordinarily constitutes 0.5-1 per cent 

 of the total nitrogen. The amount may be largely increased in disorders 

 associated with tissue waste, e.g., typhoid, acidosis, pronounced atrophy 

 of the liver, etc. For tests on amino-acids see Chapter IV. 



AROMATIC OXYACIDS 



Two of the most important of the oxyacids are parahydroxy- 



phenyl-acetic acid, 



CH 2 .COOH, 



OH 



and parahydroxy-phenyl-propionic acid, 



CH 2 .CH 2 .COOH. 



OH 



They are products of the putrefaction of protein material and tyrosine 

 is an intermediate stage in their formation. Both these acids for the 

 most part pass unchanged into the urine where they occur normally in 

 very small amount. The content may be increased in the same manner 

 as the phenol content, in particular by acute phosphorus poisoning. A 

 fraction of the total aromatic oxyacid content of the urine is in combina- 

 tion with sulphuric acid, but the greater part is present in the form 

 of salts of sodium and potassium. 



Homogentisic Acid or di-hydroxyphenyl-acetic acid, 



OH 



|CH 2 .COOH, 



OH 



*For a full discussion see Underbill's "The Physiology of the Amino Acids," Yale 

 University Press, November, 1915. 



