342 ADVENTURES IN RADIOISOTOPE RESEARCH 



Table 31. — Extent or Renewal of the Petrol-ether 

 Soluble Phosphatide Mixture -Extracted from the 



Organs of the Rabbit in the Course of 4 Hours 

 The results are computed from the figures of Tables 2 — 7. 



Organ 



Percentage of phosphatides 

 renewed during the experiment 



AC) 



B<*) 



Small intestine (mucosa) 19.6 3.7 



Liver 16.7 3.1 



Lungs 8.1 1.2 



Stomach 7.7 i 0.9 



Muscle 7.3 0.11 



Kidney 6.2 4.3 



Spleen 5.2 0.74 



Corpuscles 5.2 0.33 



Heart 4.0 0.50 



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

 ncorporation of cellular inorganic P. 



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

 ncorporation of extracellular inorganic P. 



lecithin could not be formed in the last mentioned way, since in that 

 case (see column 5 of Table 32) nine times as much labelled lecithin 

 should have been formed in the course of 12 hours than was found after 

 4 hours. Similar considerations apply to the muscle lecithin where in 

 the course of 12 hours seventeen times as much labelled lecithin should 

 have been formed as after 4 hours. Such an increase with time is highly 

 improbable. 



If we consider the two possibilities of the formation of cephalin, i. e. 

 incorporation either of cellular or of extracellular labelled inorganic P, 

 we arrive at the following result. If the labelled cephalin is formed inside 

 the liver cells, as much as 1/4 became labelled within 4 hours; thus, 

 1/4 of the total cephalin present undergoes a rapid renewal, the remain- 

 ing 3/4 being comparatively inert. In the course of the following 8 hours, 

 hardly any further increase of the amount of newly formed cephalin 

 can be noticed. That the remaining part of the cephalin is also renewed, 

 though at a very slow rate, is, however, shown by the fact that, after 

 9 days, most of the cephalin present at the start of the experiment 

 was found to be labelled. Muscle cephalin behaves in an analogous way. 



If we now consider the possibility that the labelled cephalin is formed 

 with incorporation of extracellular P, we arrive at an entirely different 

 interpretation of the results. The amount of labelled liver cephalin 

 formed in the course of 12 hours then works out to be about three times 

 that formed duiing 4 hours. This result is quite plausible. The result 

 obtained in the case of the muscle cephalin, where as much as five times 

 more labelled cephalin should have been formed in the course of 12 



