SEPARATION OP THE PUBIN BASES. 407 



formed during the demethylation of caffein and of the other higher 

 homologues. The possibility of this taking place must be conceded. 

 On the other hand it is evident that the purin group undergoes to a 

 large extent complete cleavage. These simpler products are as yet 

 unknown but it is easy to see that pyrimidin derivatives and even 

 creatinin may originate during the cleavage of purin bodies. Wiener's 

 observations on uric acid show that this purin body is not only a nuclein 

 cleavage product but that it may also be a synthetic one. Further- 

 more he has shown that uric acid is not only being made but is also 

 being constantly destroyed within the body. This process of for- 

 mation and of decomposition results in the normal minimum excre- 

 tion of uric acid (see page 344). If, however, the latter change is 

 diminished or inhibited the amount of uric acid becomes apparently 

 increased and may lead to disease conditions such as rheumatism. 

 The same view may be extended to the purin bases and the rela- 

 tively large elimination of these bodies in leukemia may be due not 

 only to increased formation but also to decreased destruction. 



For the pharmacological action of caffein and other paiins see 

 page 345. 



Caffein was discovered in 1820 by Eunge. It can be readily 

 prepared from xanthin or from either of the mono-methyl or di- 

 methyl derivatives. It has been synthesized from the mono-, di-, 

 tri-, and tetra-methyl uric acids. In other words it can be prepared 

 from uric acid direct (Fischer). It has also been synthesized from 

 di-methyl urea and cyanacetic acid (Traube). 



Separation of the Furin Bases. 



The detection and separation of the purin bases in urine offers 

 considerable difficulty which will be readily understood when it is 

 remembered that as many as fourteen of these bases have been found 

 in that secretion. Most of these, as indicated elsewhere, do not 

 represent tissue metabolism proper but rather cleavage products of 

 the purins contained in the food and drink. 



Neubauer's method, which has been employed in some modifica- 

 tion or other for the isolation of purin bases, depends upon the fact 

 that they are precipitated from an ammoniacal solution by an am- 

 moniacal silver solution. This reaction, as Kriiger has pointed out, 

 is given by all xanthin bases which contain an imido group capable 

 of substitution. It is not given by caffein, the fully methylated 

 xanthin, or by dimethyl hypoxanthin. The further separation of 

 the bases is accomplished by dissolving the silver precipitate, 

 together with a little urea, to destroy any nitrous acid, in boiling 

 nitric acid of 1.1 specific gravity. The hot solution is filtered, and 

 from the filtrate, on cooling, the "hypoxanthin fraction " of Salomon 

 — hypoxanthin, guanin, carnin, adenin, and episarkin, crystallize 

 as the corresponding silver nitrate compounds. That portion of 



