86 Intraccllular Extractives [Sept 



inosinic acid. Of the former we can say little except that it yields 

 hypoxanthin on oxidation. Inosinic acid has been known since the 

 time of Liebig, who first isolated it. Since that time it has received 

 considerable attention. Chemically it is similar to, though much 

 simpler in Constitution than, the nucleic acids in other tissues. It 

 differs from these in containing an oxypurin instead of an amino- 

 piirin radical. The work of Burian, and of Levene and Jacobs,^ 

 indicates that hypoxanthin is in gkicoside-hke combination with 

 f/-ribose. This in turn is combined with orthophosphoric acid to 

 form an ester. Other nucleic acids probably have a similar Consti- 

 tution but contain instead of ortho-phosphoric acid one of the com- 

 plex poly-basic phosphoric acids. These complex acids are united 

 with a pentose or hexose, which in turn is combined with purin 

 and pyrimidin bases. That inosinic acid plays a somewhat different 

 role in muscle than do the nucleic acids of other tissues is indi- 

 cated by the comparatively large amount in which it occurs. This 

 is much greater than would be expected from the small number of 

 nuclei in muscle. 



Carnosin, which was first obtained from extract of beef by 

 Gulewitsch and Amiradzibi,^ is a substance about whose nature and 

 significance little is known. Histidin has been isolated from the 

 products of hydrolysis of carnosin and it has been suggested that 

 carnosin is a dipeptid of histidin and alanin. Occurring as it does 

 in fairly large quantity, von Fürth and Schwartz""^ having found 

 almost as much nitrogen in the fonii of carnosin as they did in the 

 form of creatin, it is probably of considerable physiological im- 

 portance. 



The extractive that has been studied more than any other is 

 creatin. This is apparently an essential constituent of muscle. It 

 is probably the precursor of the Creatinin of the urine but the re- 

 lation between the two is not as simple as was formerly believed 

 to be the case. Folin^ has shown that the conversion of one into 



° For a general review of the biochemistry of nucleic acids, see Levene : 

 Journal of the American Chemical Society, 1910, xxxii, p. 231. 



' Gulewitsch and Amiradzibi : Zeitschrift für physiologische Chemie, 1900, 

 XXX, p. 565. 



'Von Fürth and Schwartz : Biochemische Zeitschrift, 1911, xxx, p. 413. 



*Folin: The Chemistry and Biochemistry of Kreatin and Kreatinin. Fest- 

 schrift für Olof Hammarsten, 1906 (III). 



