TURNOVER OF LECITHIN, CEPHALIN AND SPHINGOMYELIN 



339 



Tablk 27. — Spkcikio Activity ok Dii-fehent P 



Fr.\ctions in thk Rat'.s Liver 



Weight of the rat: 222 gm 



All labelled phosphate was injected subcutaneoiisly 



at the start of the experiment; 24 houre later, the 



rat was killed 



Liver fraction 



Relative specific 

 activity'"' 



Labile P . 



Lecithin P 



CephaUn P 



Non-labile acid-soluble P 

 Protein P 



100 

 117 



82 



103 



31 



<"' The figures are given relative to the labile acid-soluble P, the value of which, after 24 hours?, (;losely 

 corresponds to that of the inorganic P. 



Experiments with frogs 



The turnover figures of eephalin and lecithin extracted from the frog's 

 liver were found, as would be expected, to be lower than the correspond- 

 ing figures found in experiments with mammalia. The specific activity 

 of the eephalin P was found to be much higher than that of the lecithin P. 



Table 28. — Specific Activity of Different P 



Fractions in the Liver of a Frog 

 Labelled phosphate was injected into the lymph-sack 

 of a frog kept at 20° all through the experiment 



(4 hours) 



Ratio of specific activity of cephalin and lecithin = 6. 



Experiments with laying hens 



That, in a laying hen, the specific activity of cephalin P of the liver 

 is found, after the lapse of 5 hours, to be slightly higher than that of 

 lecithin P, while in experiments with rabbits a very great difference 

 was found, is just the result which we have to expect in view of the 

 arguments discussed on p. 335. In the course of 5 hours, the phosphatide 

 molecules present in the liver of the hen are renewed to an extent which 

 in the case of the rabbit is first reached after the lapse of many hours . 



22* 



