THE NUCLEOPROTEIDS. 



297 



others are only indirectly related to the decomposition products of nuclei ns. 

 The amount of such substances present in urine is small and varies. It 

 may be increased by a diet rich in purine bases. An increased elimination 

 of purine bases may also result from a greater destruction of leucocytes. 

 Heteroxanthine, 1 paraxanthine, 1 and Z-methylxanthine 2 are purines 

 which bear no relation to nuclein metabolism. They represent the most 

 important constituents of the so-called alloxuric bases of urine, and arise 

 from the caffeine, theobromine, and theophylline present in our table 

 accessories. The following formulae will give us an idea of the relations 

 between these substances: 



HN CO 



CO C . N . CH 3 



S C.N 



CH 



HN- 



Heteroxanthine 



= 7-Monomethyl- 



xanthine 



CH 3 . N CO 



CO C . NH 



[N C . N 



CH 



HI 



Z-Methylxanthine 



CH 3 . N CO 



CO C . N . 



HN C.1ST 

 Paraxanthine = l:7-Di- 

 methylxanthine 



CH 3 

 CH 



CH 



.CH 



CH 3 .N C 



Caffeine 



CH 3 . N C N 



Theobromine 



S 



CH 



CH 3 . N C N 

 Theophylline 



The relation of these alloxuric bases to the purine bases of tea, coffee, 

 and cocoa has been established by means of feeding experiments. 



Xanthine, hypoxanthine, guanine, and adenine are among the purine 

 bases which can be derived directly from the nucleic acids. The two 

 latter are not invariably present. They evidently appear only when 

 there is an increased decomposition of material containing nucleins with 

 relatively less oxidation. Usually they are evidently converted into the 

 corresponding oxypurines. Xanthine occasionally participates in the 

 formation of renal calculi. Pure xanthine calculi rarely occur. Uric 

 acid is usually a constituent of these bladder stones. These may occur 

 as small concretionary masses, or as large stones. They are often strati- 

 fied, in which cases uric acid layers alternate with those of calcium 

 oxalate. 



1 G. Salomon: Arch. Anat. Physiol. 1882, 426; 1886, 570. M. Kriiger and G. Sal- 

 omon: Z. physiol. Chem. 21, 169 (1895); Ber. 16, 195 (1883); 18, 3406 (1885). 



2 M. Kruger: Arch. Anat. Physiol. 1894, 553; M. Kriiger and G. Salomon: Z. physiol. 

 Chem. 24, 364 (1898). 



