RATE OF PENETRATIOX OF PHOSPHATIDES THROUGH THE CAPILLARY WALL 203 



at once, the next step being the continuous escape of the labelled phos- 

 phatide molecules through the capillary wall and their replacement 

 by other phosphatide molecules, originally located in the organs, which 

 diffuse in the opposite direction, namely through the capillary wall, 

 into the plasma. Since the phosphatide content of the plasma remains 

 practically constant during the experiment, the exodus of a certain 

 quantity of phosphatides must be followed by the influx of about th(> 

 same amount. Tn view of th(> very minute turnover of ])ho,sphatiflos 



O = first experiment 

 ■/■ = second experiment 



250 min. 



Fig. 1. Rate of disappearance of labelled phosphatide molecules 



fiom the plasma. 



in the blood, the number of labelled phosphatide molecules which an> 

 decomposed in the plasma during the experiment can be neglected. 

 The processes described above are going on under strictly physiological 

 conditions. The replacement of ordinary phosphorus (^iP) by radioactive 

 phosphorus (^^P) in some of the phosphatide molecules can certainly 

 not be considered to entail the introduction of a non-physiological com- 

 ponent into the circulation, as such a replacement cannot influence the 

 chemical l)ehaviour of the phosphatide molecules to any significani 

 extent. 



The rate at which the labelled phosphatides escape from the plasma 

 of rabbits is seen in Tables 1 and 2, and also in Fig. 1. The figures of the 

 tables were obtained by comparing the radioactivity of the phospha- 

 tides present in 1 cc. plasma samples of rabbit B, taken at different 

 intervals, with that of the phosphatides of an equal plasma volume 



