336 CHEMISTBY OF THE LEVCOMAINS. 



The studies of Fischer in 1884 on uric acid led him to consider 

 this substance as a derivative of a hypothetical body, CjH^N^, to 

 which he gave the name purin. The remarkable researches of this 

 investigator during the past few years have shown that the zanthin 

 bases are actually related to uric acid and, that they also are deriva- 

 tives of purin. This parent substance of uric acid and of the 

 xanthin bases was not prepared until 1898, although as stated, its 

 existence was pointed out fifteen years before. The term purin 

 bodies therefore includes purin and all of its derivatives. The purin 

 bodies formed in the animal organism and appearing in the urine are 

 uric acid and the several xanthin bases. The expression purin 

 bases implies the same as the older terms xanthin, nuclein or allox- 

 uric bases. 



Before considering the individual purin bases it is desirable to 

 point out the main facts bearing upon the constitution or structure 

 of the members of this group. A thorough understanding of the 

 structural relationship of these several bodies is necessary in order 

 to appreciate the r6le which they play in tissue metabolism. The 

 waste product uric acid differs from xanthin in that it contains one 

 atom of oxygen more than does the latter. Xanthin in turn differs 

 in the same way from hypoxanthin. For some time the belief has 

 prevailed that the nuclei of cells contain the physiologically impor- 

 tant xanthin bases. These bases do not exist free but rather in com- 

 bination with proteid substances forming the so-called nucleinic 

 acids, or the more complex nucleins. When the nucleins undergo 

 metabolism the purin bases are set free, suffer more or less oxida- 

 tion and leave the body partly as uric acid and partly as cleavage 

 products such as the pyrimidin bodies, creatinin, allantoin, urea, 

 oxalic acid, etc. These successive changes may be rendered appar- 

 ent by comparing the formulae of these bodies — 



POBIN, C5H4N4. 



HyPOXAUTHIN, C5H4N4O. 

 XaHTHOT, C5H4N4O2. 



TJbic Acid, CsHiN^Oij- 



Although these four substances form a homologous group it does 

 not follow that uric acid can be readily prepared by oxidation from 

 either of the preceding or that vice versa it can be reduced to these 

 bases. The statement made by Strecker that hypoxanthin by the 

 action of fuming nitric acid yields a nitro-product, which on reduc- 

 tion gives xanthin, was taken to indicate that hypoxanthin possessed 

 a constitution similar to that of xanthin. Kossel, however, showed 

 in 1882 that this conversion of hypoxanthin into xanthin did not 

 take place, and in this he was confirmed by Fischer in 1884. In 

 the same way the observation of Rheineck, reported by Strecker, 

 that uric acid is converted by sodium amalgam into xanthin, and this 

 still further reduced to hypoxanthin, has been shown to be incorrect 



