RATE OF PEXKIHATIO.N Ul PHOSPHATIDES TJlKOKiH TJIE ( APILLAUV WALL 271 



tides brought inio the circulation from tlie intestine does not suffice to 

 compensate the loss of phosphatides by the plasma due to the uptake 

 of phosphatide molecules by the liver, we can hardly expect the amount 

 released by other organs to compensate the loss of the phosphatides. 

 We have thus, to conclude that in the liver not only a very marked 

 turnover of phosphatides takes place, but that phosphatide molecules 

 exchange also with great ease between the liver cells and the plasma. 



CALCULATION OF THE AMOUNT OF PHOSPHATIDES GIVEN OFF BY 



THE PLASMA TO THE LIVER 



We saw that, after the lapse of 4 hours, 29 to 38 per cent of the label- 

 led phosphatide molecules originally present in the plasma were found 

 in the liver of rabbits. We wish to calculate from the average of these 

 figures the total amount of phosphatides which, originating from the 

 plasma, reached the liver in the course of 4 hours. When calculating this 

 amount, we must envisage that large amounts of labelled phosphatides 

 were taken up by the liver and, to some extent, by other organs as 

 well and were replaced by non-labelled ones. These process clearly lead 

 to an increase of the sensitivity of the radioactive indicator in the course 

 of the experiment. While, at the start of the experiment, 1 count indi- 

 cates, for example, 1 fx mgm phosphatide P, at the end of the experiment 

 it will indicate the presence of 5 ^ mgm. 



Let us denote by L^ the concentration of the labelled phosphatide 

 molecules of the plasma at the start of the experiment, and by L^ that 

 found after the lapse of t hours. The amount of phosphorus corresponding 

 to Lq (average of the values obtained in two experiments) w-as found to 

 be 2.4 mgm. The decrease of the labelled phosphatide content of the plasma 

 is assumed to take place according to the equation 



where X is the constant of disappearance (analogous to the decay con- 

 stant of radioactive bodies). If the liver alone would take up phospha- 

 tide molecules from the plasma, the amount of labelled phosphatides 

 which, coming from the plasma, were located in the liver, would be 

 equal to X^ — L^. As this is not the case, w^e must determine experi- 

 mentally the percentage of the labelled plasma phosphatides present 

 in the liver at the end of the experiment, which we denote by E. To 

 arrive at the figure giving the percentage of the total amount of 

 plasma phosphatide molecules {X) which were found in the liver after 

 the lapse of/ hours, we must multiply E by 



