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ADVENTURES IN RADIOISOTOPE RESEARCH 



Table 21. — Renewal of Lecithin, Cephalin and Sphingomyelin 

 Rabbit VII. — Weight: 2.4 kgm 

 Subcutaneous injection during 11.5 hours 



<i) Turnover rate calculated on the assumption that the formation of phosphatides took place with 

 incorporation of cellular inorganic P. 



("> Turnover rate calculated on the assumption that the formation of phosphatides took place with 

 incorporation of extracellular inorganic P. 



(3) Fraction extracted with cold ether. 



<^) Fraction extracted, after removal of the ether-soluble lecithin, with hot alcohol. 



Table 22. — Renewal of Lecithin, Cephalin 

 AND Sphingomyelin 

 Rabbit VIII. — Weight: 2.0 kgm 

 Subcutaneous injection during 9 days 



organs is renewed at the same rate, some fractions showing a much faster 

 turnover rate than others. These fractions could differ either in their 

 chemical composition or in their location in the cells. Numerous chemi- 

 cally different cephalins and lecithins exist differing, for example, in 

 the type of fatty acids they contain. It is, however, not probable that 

 the difference in the chemical constitution is responsible for the remark- 



