70 THE SIMPLER NATURAL BASES 



Creatine and creatinine are interconvertible. The change from the 

 former to the latter substance can be brought about quantitatively by 

 heating with acid or even without a solvent (see appendix). 



According to Gottlieb and Stangassinger [1907, 1908, i] creatine 

 is also converted into creatinine by autolytic ferments. The hydra- 

 tion of creatinine to creatine is brought about (partially) by alkalies ; 

 for instance by standing for a long time in solution in lime water 

 (Liebig), ammonia (Dessaignes), or by boiling with lead hydroxide 

 (Heintz [1849]). 



Although fresh muscle contains at most only traces of creatinine 

 (Grindley and Woods [1906], Mellanby [1908]), the evaporation 

 of the extract in the presence of the natural acids of the muscle may 

 cause a considerable anhydration to creatinine, so that the latter sub- 

 stance may be abundant in commercial meat extracts. According to 

 Grindley and Woods [1906] beef contains 0-41 per cent, fish 0-31 

 per cent., chicken O'24-o*29 per cent, of creatine ; in beef extracts they 

 found 0-55-479 per cent, of creatine and O'83-5'27 per cent, of creati- 

 nine ; the total creatine + creatinine in meat extract is however fairly 

 constant, generally about 6 per cent. Baur and Barschall [1906] 

 give as maximum 1*25 per cent, of creatine and 3 per cent, of creatinine. 



Supposed existence of several creatinines. Johnson [1892] con- 

 sidered that the creatinine from urine was not identical with that 

 obtainable from creatine, and Thesen [1898] obtained a yellow " iso- 

 creatinine " from fish. The supposed differences in these cases are 

 however due to insufficient purification, as shown by Poulsson [1904], 

 Toppelius and Pommerehne [1896] and by Korndorfer [1904, i]. 

 Similarly the xantho-, chryso-, and amphicreatinine of Gautier 

 [1896, Ch. I] were doubtless also impure, as already suggested by 

 Brieger [1886, i, p. 10, Ch. I], Indeed, no one has apparently thought 

 it worth while to re-investigate them. 



The quantitative estimation of creatinine appears to have been at- 

 tempted first by Heintz [1849]; Neubauer [1863] then worked 

 out a method depending on the isolation of the base as zinc chloride 

 compound. Salkowski showed that Neubauer's method gives results 

 which are often much too low, and proposed modifications [i 886, 1 890]. 

 Gregor [1900] attempted to utilise the copper reducing power and 

 Edlefsen [1908] has suggested a method depending on the forma- 

 tion of creatinine salicylate, but all these methods have been displaced 

 by Folin's colorimetric method, depending on the use of Jaffa's reaction 

 (see appendix). 



Since creatine can be quantitatively converted into creatinine the 



