THE NUCLEOPROTEIDS. 277 



except inosic acid (from extract of beef) which forms crystalline salts, 1 

 are amorphous and react acid. They are easily dissolved in water con- 

 taining ammonia or alkali, and form insoluble salts with the heavy metals. 



Phosphoric acid is, as we have said, quite generally found among the 

 cleavage-products of the nucleic acids. We do not know how it is united 

 in the molecule. The occurrence of representatives of the group of purine 

 bases is especially important. They vary according to their origin, and 

 the number of bases participating in the constitution of the nucleic acids 

 is also a variable one. J. Piccard 2 early met with these compounds in his 

 investigations of the nucleins. The numerous observations of A. Kossel 3 

 have indicated their wide distribution, and also the nature of the purine 

 bases present. 



We wish to state in advance that the purine bases are very closely related 

 to an important metabolic end-product, uric acid, not only from a purely 

 chemical point of view, but also because recent experiments have indicated 

 intimate biological connections. We wish, therefore, to describe briefly 

 the most important points with regard to the constitution of this class of 

 bodies. It will then be easier for us to follow the individual purine bases 

 in their course through the organism, and to judge of the part they play in 

 metabolism. 



Uric acid, the earliest known member of this series, was discovered in 

 urine and bladder stones, as far back as 1776, by Scheele 4 and Bergmann. 5 

 We will add that Pearson 6 has shown the presence of uric acid in "chalk- 

 stones," and that Fourcroy and Vauquelin 7 shortly after proved it to be an 

 essential constituent of the excrement of birds. Finally William Prout, 8 

 in 1815, found that the excrement of the boa-constrictor contained as 

 much as 90 per cent of uric acid. 



Uric acid was thoroughly investigated by Liebig. A large number of 

 its important decomposition products also became known, without, how- 

 ever, indicating the true constitution of the acid itself. Wohler and Liebig 9 

 mention its close relation to allantoine, even then regarded as a component 

 of the allantoic fluid. They obtained urea and alloxan by treating uric acid 



1 J. von Siebig: Ann. 62, 317 (1847) and Haiser: Monatsh. 16, 190 (1895). 



2 J. Piccard: Ber. 7, 1714 (1874). 



3 A. Kossel: Z. physiol. Chem. 4, 290 (1880); find. 7, 7 (1882); find. 10, 248 (1886); 

 12, 241 (1888). 



4 K. W. Scheele: Examen chimicum Calculi urinarii, Opuscula II, 73 (1876). 



6 T. Bergmann: Opuscula IV, 232 (1876). Cf. E. Fischer: Ber. 32, 435 (1899). Cf. 

 also Synthesen in der Purin- und Zuckergruppe, F. Vieweg & Sohn, Braunschweig, 

 1903, and Untersuchungen in die Puringruppe (1882-1906), J. Springer, Berlin, 1907. 

 K. Bunte: Inaug. Diss. Berlin, 1905. 



8 Pearson: Phil. Trans, of the Royal Soc. London, 15, 1798. 



7 Ann. de chim. 56, 258 (1905). 



8 Ann. Phil. 5, 413 (1815). 



9 Ann. 26, 241 (1838). 



