FORMATION- OF PHOSPHATIDES IX THE BKAIX TISSUE OF ADILT ANIMALS 24 7 



The total phosphorus present, amounting lo 1.39%, is distributed 

 between protein, phosphatides and acid soluble compounds in tiie iollow- 

 ing manner. 



Protein P 6.8% 



Phosphatide P 67.6% 



Acid soluble P 25.6%, 



the largest amount of phosphorus being thus present as phosphatide. 

 Let us assume that labelled sodium phosphate is introduced per os or 

 by injection into the animal body and that after the lapse of some 

 time some of the inorganic phosphorus present in the brain tissu(> is 

 found to be labelled. Such an observation is not to be interpreted as 

 a formation of new brain tissue because the inactive phosphate ions 

 can be replaced by labelled ones through a simple exchange process. 

 The phosphate present in the lecithin molecule cannot, however, be 

 replaced through a simple exchange process i.e. the labelled phos- 

 phate can only enter the lecithin molecule during a synthesis of the 

 latter. The presence of labelled lecithin molecules in the brain is there- 

 fore a proof that a synthesis of lecithin has taken place after the intro- 

 duction of the labelled sodium phosphate into the animal body. Though 

 it was highly improbable that the phosphate present in the lecithin- 

 molecule could be replaced by labelled phosphate through a physical 

 exchange process, we tested this point by carrying out the following 

 experiment. We shook 10 cc. of cats blood at 37" for 4 hours with 

 2.5 cc. of isotonic sodium chloride solution containing labelled phos- 

 phorus. 10 cc. of blood contain about 1.2 mgm of phosphatide and 

 0.4 mgm of inorganic phosphorus, the latter being labelled by the 

 activity added. The lecithin was then extracted. The extraction was 

 made with ether -f- alcohol and the extract was shaken for several 

 hours with calcium phosphate to remove any inorganic labelled 

 phosphate which might be present in the extract. Of the 10,000 

 radioactive units only 3 units were found in the blood phosphatide 

 extracted. Even this very slight exchange is probably due to en- 

 zymatic actions occurring in the blood. From an experimental point of 

 view blood seemed to be a very suitable liquid to carry out an exchange 

 experiment and as the exchange observed was only a very slight 

 one it did not seem of interest to pursue the subject further and carry 

 out exchange experiments in liquids from which enzymes had been 

 removed. In this connection we may, however, mention an experiment 

 in which blood containing labelled phosphate was allowed to circulate 

 through an isolated liver. 



Professor Lundsgaard being engaged on liver perfusion experi- 

 ments kindly added a solution (3 cc.) containing labeUed phosphorus 

 of negligible weight to the blood used in his experiments. In 10 cc. 



