TURNOVER OF LECITHIN, CEPHALIN AND SPHIN(;OMVRTJN 



335 



able difference in the turnover rate of the different cephahn fractions. 

 The specific activity of successive fractions of cephalin (^rystalHsed 

 repeatedly from alcoholic or other solutions docs not vary appreciably 

 (comp. p. 341). A much more probable explanation of the difference 



Tablk 23. — Renewal of Lecithin and Ckphalin 

 Rabbit IX. — Weight: 2.. 5 kgm 

 Subcutaneous injection during 50 daj'S 



<'' Calculated on the assumption of formation inside the cells (with incorporation of plasma inorganic P). 

 ''' Calculated on the assumption of formation outside the cells (with incorporation of plasma inorganic P). 



20- 



10- 



12 Hours 

 Fig. 5. Turnover of lecithin and cephalin in the liver. 



mentioned above is that in some parts of the cell a decidedly more 

 pronounced enzymatic breakdown and building up of cephalin takes 

 place than in others. In experiments of short duration, we mainly mea- 

 sure the rejuvenation taking place in these favoured districts. The beha- 

 viour of lecithin is different in that we do not encounter such a pronoun- 

 ced variation in the rate of turnover of different fractions. The average 

 lecithin molecule is, however, renewed at a similar rate as the average 

 cephalin molecule. This explanation is suggested by the fact that, while 



