314 BACTERIAL POISOKS. 



Now that uric acid has been prepared synthetically, this 

 forms the final step in the complete synthesis of xanthine. 

 By further action of nascent hydrogen the xanthine in turn 

 is converted into hypoxanthine. The reverse operation, 

 the conversion of hypoxanthine into xanthine, though re- 

 ported by Streckeb has not been confirmed by Fischer 

 or by KosSEL. It is, therefore, evident that these bodies 

 form a continuous oxidation series with uric acid as the 

 final product. Although this change is unquestionably the 

 one which goes on in the animal economy, yet all attempts 

 to reproduce it in the laboratory by oxidation with potas- 

 sium permanganate or nitric axiid have apparently yielded 

 only negative results. Again, xanthine may be prepared 

 from guanine by putrefaction of the latter, or by oxidation 

 with nitrous acid. The change may be represented by this 

 equation : 



C,H,Np + HNO, = QH.NA + N^ + H,0. 



GuANiNK. Xanthine. 



This reaction, first described by Strboker (1858), corre- 

 sponds exactly to the one by which Kossel has transformed 

 adenine into hypoxanthine (see page 289). 



Gautier, starting out on the hypothesis that xanthine 

 is a polymerization-product of hydrocyanic acid, has en- 

 deavored to prepare it directly from this compound. In- 

 deed, he claims to have succeeded in effecting the synthesis 

 of not only xanthine, but also its homologue, by simply 

 heating hydrocyanic acid in a sealed tube with water and a 

 little acetic acid, the latter being added to neutralize any 

 ammonia that might form. He expresses the reaction as 

 follows : 



llHCl^ + iHfi = CgH^N^Oj + CgHeNPa + SNH,. 



Xanthine. Methtl-xanthine, 



l^early all of the methods that have been employed for 

 the preparation of xanthine are based upon its precipitation 

 as the insoluble silver compound. From the urine it can 

 be isolated according to the method given under paraxan- 

 thine, on page 322. It may also be obtained from the 



