TURNOVER OF LECITHIN, CEPHALIN AND SPHINGOMYELIN 



337 



plasma and the interspaces. The extracellular space of the brain tissue 

 was calculated from the chlorine or sodium distribution to amount to 

 30 per cent of the weight of the tissue<i\ 



Table 24. — Formation of Labellkd PHO.snrATini-s ix titf: Brain of thk KAumr 



In view of the foregoing statements, we cannot give exact figures 

 for the specific activity of the extracellular and cellular inorganic P 

 of the brain. Since these figures enter the calculation of the turnover 

 rate of the brain phosphatides the calculation cannot be carried out. 

 A further complication arises from the fact that the decomposition of 

 the brain creatinephosphoric acid prior to the extraction of the inorga- 

 nic P could not be avoided in our experiments. The brain creatine P 

 may be appreciably less active than the brain inorganic P. This fact 

 would lead to a dilution of the labelled inorganic P by non-labelled 

 inorganic P. We record, therefore, in Table 24, a) the specific activity 

 of the brain phosphatide P relative to the plasma inorganic P, h) relative 

 to the brain total inorganic P, and c) relative to the liver phosphatide P. 

 While the brain phosphatides are found to be much less active than the 



Table 25. — Formation of Labelled Lecithin and Cephalin 

 IN the Brain of the Rabbit 



Kelative specific activity 



<•) In this case, the total activity was injected at the start of the experiment. 



<i^ J. F. Manery and B. Hastings, J. Biol. Chem. 127, 657 (1939). 



22 Hevcsy 



