264 ADVENTURES IN RADIOISOTOPE RESEARCH 



of rabbit A. The phosphatides were extracted by making use of Bloor's 

 method. After being converted into phosphate by wet ashing, an aliquot 

 part of the solution obtained was used in the colorimetric measurement 

 of the P content, another to secure an ammonium magnesium phosphate 

 precipitate, the activity of which was determined by a Geiger counter. 

 The calculation of the amount of labelled phosphatides present in 

 Ihe total plasma of the rabbit from that found in 1 cc. necessitates 

 the knowledge of the total plasma volume. This was calculated from the 

 blood volume and the known haematocrit value. The blood volume was 

 determined by making use of a method recently described (Hahn and 

 Hevesy, 1940). This method is based on the measurement of the dilution 

 of a known volume of corpuscles containing labelled organic P compounds 

 in the circulation of the animal, the blood volume of which is to l)c 

 determined. In experiments on rabbits, the injection of foreign plasma 

 was preceded by the removal of a corresponding volume of blood, as 

 described above. In experiments on chicks, however, no blood was 

 removed beforehand. 



EXPERIMENTS ON RABBITS(i^ 



(1) Some of the results obtained were previously published bj' us in a note to 

 Nature 144, 204 (1939). — F. E. Haven and W. F. Bale [J. Biol. Chem. 129, 23 

 (1939)] injected emulsions containing labelled phosphatides prepared from the 

 liver of the rat into the circulation of another rat and found the labelled phospha- 

 tides to accumulate mainly in the liver and the spleen. 



As seen in Tables 1 and 2 and also in Fig. 1 , half of the labelled phosphatides 

 introduced into the plasma leave the circulation by penetrating through the capil- 

 lary wall in the course of about an hour. As the non-labelled phosphatides can be 

 expected to show the same behaviour as the labelled ones, we can conclude that, 

 from aU phosphatide molecules present at the start of the experiment in the 

 plasma, half will no longer be present after the lapse of about an hour, and will 

 be replaced by others which were previously' located in the organs. 



Table 1. — Rate of Escape of Labelled 

 Phosphatides through the Capillary 

 Wall of a Rabbit Weighing 2.4 kgm 



First experiment 



Time 



Per cent of labelled phos- 

 phatides injected into the 

 jugular vein, present in 

 the total plasma 



mill. 

 30 „ 



82 ., 



100 



ti.5..S 

 39.8 



120 „ 27.2 



247 „ . 17.6 



