554 WASTE-PRODUCTS 



one, depending upon the reduction of the concentration of the urates 

 in the tissue-fluids, and the tendency of the tissue-enzymes to spon- 

 taneously reestablish the normal equilibrium between the blood and 

 the tissues. 



The only amino-acid which normally occurs in urine is Glycocoll, 

 or amino-acetic acid, which, in very small amounts, appears to be a 

 constant constituent. If, however, an excess of leucine or alanine be 

 introduced into the circulation they will appear in the urine. It would 

 appear that, normally, deaminization and utilization are too rapid to 

 permit of the accumulation of amino- acids in the blood in sufficient 

 amount to cause elimination by the kidneys. If, however, the rate of 

 deaminization be slowed, as, for instance, in degenerative changes of 

 the liver induced by chloroform-necrosis or phosphorus-poisoning, then 

 a variety of amino-acids may appear in the urine. It is also stated by 

 Loewy that the amino-acid content of the urine is increased at high 

 altitudes. 



When the urea, creatinine, uric acid and glycocoll of the urine are 

 added together, there is always a considerable remainder of nitrog- 

 enous excretion. Part of this arises from the sulphur-containing and 

 conjugated excreta which are about to be described, part is stated by 

 Abderhalden and Pregl to be present in the form of Polypeptides which 

 yield glycocoll, leucine, alanine, glutamic acid and phenylalanine on 

 hydrolysis. When all the nitrogen in hitherto defined substances is 

 summed up, however, there is still a small remainder which, although 

 it arises from substances excreted in small amount, may nevertheless 

 be of physiological importance. It is derived in part from exogenous 

 and in part from endogenous metabolism. 



CONJUGATED EXCRETA. 



A variety of substances occur in the urine which arise from the 

 union of a genuine excretory product with another molecule which 

 serves as a vehicle to accomplish its elimination. Such excreta are, 

 for example, the Conjugated Glucuronic Acids which are normally pres- 

 ent in the urine in small amounts and are greatly augmented by the 

 ingestion of certain poisons, of which a partial list has been given in a 

 previous chapter (Chapter III). The function of the glucuronic acid 

 moiety of the molecule appears to be in the main to render harmless 

 the associated substance which is usually of a toxic character. Only 

 definite classes of toxic substances are eliminated in this manner, 

 however. 



The Glucuronates which normally occur in the urine are in the main 

 the phenyl, indoxyl and skatoxyl glucuronates, the latter two in very 

 small amounts, The phenol, indoxyl and skatoxyl radicals are derived, 

 it is believed, mainly from putrefactive decomposition of aromatic 

 amino-acids, particularly tyrosine and tryptophane, by the intestinal 

 bacteria. These substances are in themselves very toxic, but their 



