248 ADVEXTURES IN RADIOISOTOPE RESEARCH 



of blood used for 4 hours, 7 of the 10,000 radioactive units added were 

 found in the isolated lecithin phosphorus; the liver perfusion has thus 

 a positive effect on the formation of labelled lecithin. 



We may also mention that in 1 cc. of the blood of a cat killed li.> 

 hours after injecting a negligible weight of labelled phosphorus, we found 

 a lecithin phosphorus activity amounting to 2 % of the activity found 

 in 1 cc. of plasma, while the acid soluble phosphorus present in 1 cc. 

 of blood corpuscles contained, as Professor Lundsgaard found, an 

 activity of 12.5% of that of the plasma, about 2/3 of this being present 

 in the phosphorus esters. A detailed study of the distribution of the 

 labelled phosphorus between plasma and blood corpuscles is being carried 

 out by Professor Lundsgaard and one of the present writers. 



EXTRACTION OF PHOSPHATIDES 



The usual method of extracting phosphatides is by means of alcohol- 

 ether mixtures. In this method of extraction a small part of the 

 inorganic phosphorus present is dissolved as well; but in view of the 

 preponderance of phosphatide phosphorus in the brain the error thus 

 introduced can generally be disregarded. Under the peculiar condi- 

 tions which prevail in the investigation of the formation of labelled 

 phosphatides the error mentioned above can however become very 

 embarassing. We introduce labelled inorganic phosphorus into the 

 animal body per os or by subcutaneous injection. Now it is possible 

 that only a very small amount of this is converted into labelled phos- 

 phatide phosphorus so that even of a trace of the labelled inorganic 

 phosphorus is extracted by the alcohol-ether mixture, our results can 

 be seriously falsified. This is best seen from the following example: 

 brain tissue is shaken in vitro with a solution of labelled inorganic 

 phosphorus containing 10,000 relative radioactive units, and 0.1 mgm 

 phosphorus; the solution is then removed and the dried tissue extracted 

 with alcohol -j- ether. The presence of as little as 10~* mgm of in- 

 organic phosphorus in the extract corresponds to 10 relative radioactive 

 units and may be partly or wholly responsible for the activity of the 

 extract. For this reason, although conditions in experiments in vivo 

 are much more favourable than those in the example above, we chose 

 a method of extraction more suitable for our special case than the alcohol- 

 ether extraction. 



The procedure adopted by us was as follows. We dried the brain 

 tissue with acetone and extracted the phosphatides by prolonged shaking 

 with carefully dried ether; the extract obtained was evaporated to 

 dryness and dissolved a second time in ether in the presence of a large 

 excess of finely powdered dry sodium phosphate. We had found that 



