MESOXALIC DI-UEEIDES. 139 



prove possible to prepare xanthine advantageously from uric acid, 

 still the fact of its close relationship thereAvith would lead us to 

 expect its more abundant existence than has hitherto been ima- 

 gined particularly, for instance, in the excreta of those animals 

 whose normal mode of tissue-waste results in the production of 

 uric acid rather than of urea. 



(146.) This expectation is strengthened by the extraction from 

 guano, the well-known dried excrement of sea-fowl, of a feeble 

 base called guanine, which bears to xanthine the same often- 

 referred-to relation that ammonia bears to water, as shown in the 

 following series of formulae : 



C 5 N 4 H 3 (H)0 Hypoxanthine. 



C S N 4 H 3 (HO)0 Xanthine. 



C 5 N 4 H 3 (H 2 N)0 Guanine. 



C 5 N 4 H 3 (HO) 3 Uric acid. 



Just, in fact, as uric acid, and doubtless xanthine, yield by oxi- 

 dation parabanic acid and urea, so does guanine yield by oxidation 

 parabanic acid and amido-urea or guanidine,* thus : 



Xanthine Parabanic Urea 



C 5 N 4 H 3 (HO)0 + H a O + 3 = C 3 N 2 H 2 3 + CN a H 3 (HO) + C0 2 ? 



G-uanine Parabanic Guanidine 



C 3 N 4 H 3 (H 3 N)0 + H 2 + 3 = C 3 N 4 H 2 3 + CN a H 3 (H 2 N) + C0 a . 



Moreover, xanthine itself occurs in small quantity as a secondary 

 product of the above oxidation of guanine, and may be obtained 



* By the oxidation of kreatine, which has been already described as a 

 polymerone of glycolic acid, methylamine, and urea, its glycolic residue is 

 converted into oxalic acid, while its methylamine and urea residues are left 

 in combination to form methylainido-urea or methyluramine, a compound 

 homologous with amido-urea or guanidine, thus : 



CN 3 H 3 (HO) Urea. 



CN 2 H 3 (H 3 N) Guanidine. 



CN 2 H 3 (CH 3 HN) Methyluramine. 



Again, biuret C 2 N 3 H 5 O a , or C 2 N.5H 3 (H s lS[)O a , may be regarded as carbo- 

 guanidinic acid, just as allophan C 2 N 3 H 4 3 or CaN a H 3 (HO)0 2 is regarded as 

 carb-ureic acid. 



