CHEMICAL BASIS OF THE ANIMAL BODY. 1265 



regarded by plant-physiologists as waste-products of the vege- 

 table organism, and are thus found chiefly in those parts of the 

 plant which are on their way to removal, viz. the bark, leaves 

 and seeds. 



1. Xanthine. 



C 6 H 4 N 4 2 . 



NH- CH 



CO C — NH 



NH— C= N 



CO. 



First discovered in a urinary calculus, and called xanthic 

 oxide. More recently it has been found as a normal, though 

 very scanty, constituent of urine, muscles, and several other 

 tissues, such as the liver, spleen, thymus, brain-substance, etc. 

 It occurs in larger quantities, together with hypoxanthine, in 

 'extract of meat,' and is also found in traces in vegetable tis- 

 sues, — lupins, malt seedlings and tea. In nearly all cases it 

 is accompanied by hypoxanthine. The amount which is pres- 

 ent in any of the above tissues and fluids is so small that none 

 of them, except perhaps the extract of meat, affords a con- 

 venient source for its preparation. To obtain it in quantity 



Fig. 217. Xanthine hydrochloride, 

 C 5 H 4 N 4 0.2.HC1. (Kiilme.) 



Fig. 218. Xanthine nitrate, 

 C 5 H 4 N 4 2 . HKOs. (Kiilme.) 



guanine is treated with nitrous acid, and the nitro-product thus 

 obtained is reduced in ammoniacal solution with ferrous sul- 

 phate. It may also be prepared artificially from hydrocyanic acid 

 and water in presence of acetic acid. When pure it is a colour- 

 less powder, requiring about 14,000 parts of water for its solution 

 at ordinary temperatures and 1400 at 100°. Insoluble in alcohol 

 and in ether, it dissolves readily in dilute acids and alkalis 

 (characteristically in ammonia) forming crystallizable com- 

 pounds. 



Reactions. The discrimination of members of the xanthine 

 group is not easy, since, from their close relationship, they yield 

 many reactions in common. The following are characteristic 

 of xanthine. 



i. WeideVs reaction. The substance is warmed with freshly 

 prepared chlorine-water and a trace of nitric acid as long as any 

 gas is evolved: it is then carefully evaporated to dryness and, 

 if xanthine is present, the residue turns pink or purplish-red 



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