GUANIN. 379 



tion in the fact that both are substituted guanidins. Creatin is 

 regarded by Hoppe-Seyler as an intermediate product in the forma- 

 tion of urea, and a similar rdle probably belongs to guanin. It has 

 already been pointed out (p. 336) that the purin bases may break 

 up in part into pyrimidin bodies and these in turn may yield sim- 

 pler products. It is therefore possible for guanin to thus yield crea- 

 tinin which on hydration would give creatin. The formation of the 

 latter from hexon bases such as arginin is a like possibility. The 

 observation of Wiener that uric acid is destroyed by the muscle 

 and kidney of herbivora (beef, horse) and by the liver of carniv- 

 ora (dog, hog) emphasizes a like action of the muscles with respect 

 to the purin bases. From Stadthagen's experiments on dogs we 

 know that guanin ingested produces an increase in the amount of 

 uric acid and urea excreted, and the same is also true of the nuclein 

 derived from yeast. These results have led him to the conclusion 

 that in mammals uric acid is a direct, or more or less altered cleav- 

 age product of proteids, notwithstanding the fact that in birds it is 

 the result of synthesis in the liver (page 344). 



Guanin as ordinarily obtained, when ammonia is added to a solu- 

 tion of a salt, forms a white amorphous powder. According to 

 Horbaczewski * it can be obtained in a crystalline form by dissolving 

 the powder in a warm dilute alkali (1-2000), adding about one third 

 volume of alcohol and then acidulating with acetic acid. Any cloudi- 

 ness that forms is removed by filtration, after which the clear filtrate 

 is allowed to stand. In time the guanin crystallizes in rather large 

 roundish or irregular aggregates which resemble those of creatinin 

 zinc chlorid and consist of long prisms or pyramids microscopically 

 quite unlike those of xanthin. The crystals contain no water of 

 crystallization. 



The free base is insoluble in water, alcohol, ether, and ammonium 

 hydrate ; easily soluble in mineral acids, fixed alkalis, and in excess 

 of concentrated ammonium hydrate. It can be heated to above 200° 

 without undergoing decomposition. When evaporated with strong 

 nitric acid it gives a yellow residue, and this on the addition of 

 sodium hydrate assumes a red color, which on heating becomes 

 purple, then indigo-blue ; on cooling it returns to a yellow, passing 

 through purple and reddish-yellow shades, due, according to v. 

 Briicke, to absorption of water. This, the so-called xanthin reaction, 

 was supposed to be due to the formation of xanthin and a nitro- 

 product. It is given best by guanin, then by xanthin, and is not 

 given by either hypoxanthin or adenin. 



Nitrous acid converts it directly into xanthin, thus : 



C,H,N,0 + HNO, = C,H,Np, -F N, -f- Up. 



This reaction is identical with that of adenin, whereby hypo- 



^Zeiis. physiol. Ghem., 23, 226, 1897. 



