ii6o THE METABOLISM OF NUCLEIN AND [pt. iii 



10-4. Creatinine, Creatine and Guanidine 



The presence of creatine and creatinine in the unincubated avian 

 egg was at one time a matter for dispute. In 191 1 Salkovski and 

 Kojo independently reported the existence of traces of creatinine in 

 the fresh egg, akhough four years before Mellanby had completely 

 failed to find any there. However, there has always been agreement 

 that organised embryonic tissues contain creatine and creatinine. 

 Krukenberg in 1880 detected the presence of the latter substance in 

 the muscle tissue of foetal calves at various ages. Later, Mendel & 



Days->5 10 



Fig. 356. 



Leavenworth isolated 0-03 per cent, creatine from the muscles of a 

 265 mm. foetal pig — a low figure, the adult value being 0-45 per 

 cent. Mellanby himself estimated the creatinine in the embryonic 

 chick from the 14th day onwards, and some years later I obtained a 

 series of figures parallel with his, but rather lower. These are shown 

 in Fig. 354. There was little doubt but that the substance was present 

 from the very beginning of development, and in 1924 Tiegs was able 

 to demonstrate it by a colour test in the heart of the 4th-day embryo 

 and in the general body tissue on the 5th day. Still later Fiske & 

 Boyden reported a soUtary value for the 8th day of development, also 

 shown in Fig. 354, 



