CHEMICAL BASIS OF THE ANIMAL BODY. 1267 



in caustic soda. It also yields with hydrochloric acid a rela- 

 tively insoluble salt which crystallizes readily, whereas the 

 corresponding salt of paraxanthine is readily soluble. They 

 may by this means be separated the one from the other. 



Heteroxanthine does not give the ordinary reaction for xan- 

 thine with nitric acid and caustic soda, but yields a brilliant 

 coloration on the application of Weidel's test (see sub xan- 

 thine). Like the other xanthine bases it gives an insoluble 

 salt with an ammoniacal solution of nitrate of silver. 



3. Paraxanthine. C 7 H 8 ]M" 4 2 . (Dimethylxanthine.) Isom- 

 eride of Theobromine. 



Like heteroxanthine it occurs in very small amounts in urine. 

 It is soluble with difficulty in cold water, but is more soluble 

 than xanthine; is much more soluble in hot water, insoluble in 

 alcohol and in ether. It crystallizes readily in characteristic 

 flat, somewhat irregular, six-sided tables when its solutions are 

 slowly evaporated, or in needles if rapidly. It forms, as do the 

 preceding subtsances, a crystalline salt with nitrate of silver; 

 this like the corresponding compound of xanthine is soluble in 

 strong nitric acid (sp. gr. 1*1) at 100°, and may thus be sepa- 

 rated from hypoxanthine. It may be separated from xanthine 

 by means of its greater solubility in cold water, and from 

 heteroxanthine by the difference in the solubility of its salts 

 with sodium and hydrochloric acid. 



Paraxanthine gives Weidel's reaction but not the ordinary 

 xanthine test with nitric acid and caustic soda. 



4. Carnine. C 7 H 8 N 4 3 . 



Closely allied in composition to the preceding base, but as 

 yet of unknown constitution, carnine occurs only as a constitu- 

 ent of 'extract of meat," of which it forms about one per cent., 

 although it has been stated to occur also in urine (?). 



It crystallizes in white masses composed of very small 

 irregular crystals ; it is soluble with great difficulty in cold, 

 readily soluble in hot water, insoluble in alcohol and in ether. 

 It unites with acids and salts to form crystallizable compounds. 

 Of these the more important are the salts with basic lead 

 acetate, soluble in boiling water, and with nitrate of silver, 

 insoluble in strong nitric acid and ammonia. Carnine gives 

 Weidel's reaction when only a small amount of chlorine water 

 is employed, but the test fails if any excess is used. 



Carnine bears an interesting relationship to hypoxanthine, 

 into which it may be converted by treatment with chlorine or 

 nitric acid, or still more readily by bromine. 



C 7 H 8 N 4 3 + Br 2 = C 5 H 4 N 4 . HBr + CH 3 Br + C0 2 . 



