572 



THE CHEMISTR Y OF THE URINE. 



If two salts contain an electrical ion in common (or without great inac- 

 curacy we may say, a base or acid in common), each decreases the solubility 

 of the other, whereas salts which contain no base or acid in common 

 may mutually increase each the other's solubility. Thus the presence of 

 sodium chloride in solution will diminish the solubility of sodium urate, 1 

 and ammonium chloride that of ammonium urate ; but the presence of 

 either of these chlorides will increase the solubility of (say) calcium 

 phosphate. These laws will be found to have important application in 

 the explanation of certain urinary phenomena. 



In addition to products which arise from metabolism in the tissues, 

 the urine contains substances which are derived more directly from the 

 ingesta. These comprise a large proportion of the normal inorganic 

 constituents, which are always found ir*the diet in excess of the needs 

 of the organism ; and they may consist also of substances accidental or 

 accessory to the diet, or again of drugs, or of substances experimentally 

 introduced into the body. 



Some of these, while taking no share in metabolism proper, may 

 form " conjugated " or synthetic compounds with certain intermediate 

 products of metabolism, and so modify excretion. Thus glycin and 

 glycuronic acid are substances capable of easy oxidation in the body, 

 and are therefore not properly terminal products of metabolism ; but 

 they are protected from oxidation and are eliminated as synthetic 

 compounds with certain aromatic substances, whenever the latter are 

 absorbed in sufficient quantity from the bowel. 



QUANTITATIVE COMPOSITION OF THE URINE. 



The figures which follow are from the well-known table given by 

 Parkes, representing the normal twenty-four hours' excretion of the chief 

 urinary constituents : 



In the following analyses, derived from Bunge, all the figures were 

 obtained from the same individual. They represent the twenty-four 

 hours' excretion of a young man ; in the one case, upon a diet con- 

 sisting entirely of beef with a little salt and spring water; in the 



1 As was shown experimentally by Sir William Roberts, before the general principle 

 enunciated above had been developed by Nernst. 



