PURINE BASES. 713 



constant for the same individual. According to SiVEN, 1 with purine-free 

 diet the elimination of purines is lowest at night and highest in the morn- 

 ing hours. Rest and work do not show any positive difference. As 

 the four true nuclein bases have been treated in Chapter II, it only 

 remains to describe the special urinary purine bodies. 



HN CO 



I I 

 Heteroxanthine, C 6 H6N 4 2 , 7-monomethylxanthine, OC C.N.CH 3 , was first 



CH 



HN C.N 



detected in the urine by SALOMON. It is identical with the monomethylxan- 

 thine which passes into the urine after feeding with theobromine or caffeine. 

 SALOMON and NEUBURG 2 found heteroxanthine in the urine of a dog fed entirely 

 upon meat, and this was probably formed by a methylation in the body. 



Heteroxanthine crystallizes in shining needles and dissolves with difficulty 

 in cold water (1592 parts at 18 C.). It is readily soluble in ammonia and alkalies. 

 The crystalline sodium salt is insoluble in strong caustic alkali (33-per cent) and 

 dissolves with difficulty in water. The chloride crystallizes beautifully, is rela- 

 tively insoluble, and is readily decomposed into the free base and hydrochloric 

 acid by water. Heteroxanthine is precipitated by copper sulphate and bisul- 

 phite, mercuric chloride, basic lead acetate and ammonia, and by silver nitrate. 

 The silver compound dissolves rather easily in dilute, warm nitric acid; it crystal- 

 lizes in small rhombic plates or prisms, often grown together, forming charac- 

 teristic crosses. Heteroxanthine does not give the xanthine reaction, but does 

 give WIEDEL'S reaction, according to FISCHER (see Chapter II). 



CH 3 .N CO 



! I 



l-Methylxanthine, CH 6 N40 2 , OC C.NH , was first isolated from the 



urine and studied by KRUGER, and then by KRUGER and SALOMON. 3 It is diffi- 

 cultly soluble in cold water, but readily soluble in ammonia and caustic soda, 

 and does not give an insoluble sodium compound. It is readily soluble in dilute 

 acids, and it crystallizes from its acetic-acid solution in thin, generally hexagonal 

 plates. The chloride is decomposed into the base and hydrochloric acid by 

 water. 1-methylxanthine gives crystalline double salts with platinum and gold. 

 It is not precipitated by basic lead acetate, nor when pure by basic lead acetate 

 and ammonia. With ammonia and silver nitrate it gives a gelatinous precipitate. 

 The silver-nitrate compound crystallized from nitric acid forms rosettes of united 

 needles. With the xanthine test with nitric acid it gives an orange coloration 

 on the addition of caustic soda. It gives WEIDEL'S reaction (according to FISCHER) 

 beautifully. 



CH..N CO 



I I 

 Paraxanthine, C 7 H 8 N 4 02, 1.7-dimethylxanthine, OC C.NCH 3 , urotheo- 



HN C. 



bromine (THUDICHUM), was first isolated from the urine by THUDICHUM and 



1 Skand. Arch. f. Physiol., 18. 



2 Salkowski's Festschrift, Berlin, 1904. 



3 Kriiger, Arch. f. (Anat. u.) Physiol., 1894; Kriiger and Salomon, Zeitschr. f. 

 physiol. Chem., 24. 



