330 ADVENTURES IN RADIOISOTOPE RESEARCH 



lecithin is not. It was even reported^^) that cephalin prepared from cattle- 

 blood or cattle-brain enhances, while lecithin inhibits the clotting of 

 rabbits blood. The role of the phospholipids as transport agents of fats 

 was much discussed, this role being often ascribed to lecithin alone. 

 In our first experiments, we determined the turnover rate of lecithin 

 and cephalin in the organs of rabbits 4 hours after intravenous injection 

 of labelled phosphate. We found the turnover rate of cephalin extracted 

 from the liver, the intestinal mucosa and other organs to be pronoun- 

 cedly faster than that of lecithin. Simultaneously, Chargaff^^) found 

 the rate of rejuvenation of cephalin extracted from the liver and the 

 intestinal tract of rats to be slower than that of lecithin. We were first 

 inclined to explain this difference in the findings of Chargaff and 

 ourselves by the fact that the former investigated the turnover process, 

 in contradistinction to us, in carnivorous animals. We soon found, 

 however, that it is the duration of the experiment which is decisive for 

 the higher or lower rate found for the cephalin turnover. We will, in what 

 follows, first describe the experimental procedure used. 



Experimental procedure 



The tissue is dried with cold acetone and extracted first with ether 

 and then with boiling alcohol. The second process is repeated several 

 times. The solutions obtained were evaporated to dryness and taken up 

 by petrol-ether in the presence of pulverised dry sodium phosphate. 

 The latter was added in order to remove traces of active phosphate 

 possibly present. The process was then repeated in the absence of phos- 

 phate and the dry residue taken up in ether. The next step was to pre- 

 cipitate the cephalin from the solution by adding 96 per cent alcohol. 

 The filtrate obtained was evaporated and the residue containing lecithin 

 extracted with ice-cold alcohol. This procedure was repeated and the 

 purified lecithin obtained precipitated as chloro-cadmium-lecithin. The 

 compound obtained was thoroughly washed with ether in order to remove 

 traces of chloro-cadmium-cephalin possibly present. 



The cephalin was prepared from the alcoholic precipitate obtained 

 in the early treatment of the phosphatide mixture. To obtain pure 

 cephalin the precipitate was repeatedly dissolved in ether and precipi- 

 tated with alcohol. 



To secure sphingomyelin the fraction insoluble in petrol-ether was 

 collected and treated alternatively with ether and ice-cold alcohol. 

 The last residue thus obtained was dissolved in a mixture of methyl 

 .alcohol and chloroform. By adding ether to this solution purified sphingo- 



^i^Y. Ok.\rmura, Mitt. med. Oes. Okoyama 48, 1585 (1936). 

 ^2)E. Chargaff, J. Biol. Chem. 128, 592 (1939). 



