RELATIONSHIP OF PHOSPHOLIPINS TO SYNTHESIS 463 



plasmic material must be established, a disproportion which subsequent 

 development corrects. 



The Synthesis of Nuclear Material is a self-accelerated or autocatalyzed 

 phenomenon. This follows from the fact that each successive cell 

 division occupies about the same length of time as the preceding one, 

 but the number of nuclei which results from the divisions is at each 

 division twice as great as in the preceding one. The rate of production 

 of nuclei therefore forms a geometrical progression in time intervals 

 which constitute an arithmetical progression. The synthesis of nuclear 

 material thus evidently accelerates the formation of fresh nuclear 

 material- (Loeb.) 



The question now presents itself as to the origin of the materials 

 from which the nuclei are synthesized. The most characteristic 

 constituent of the nucleus is Nucleic Acid which is built up by the 

 combination of purine bases, a carbohydrate radical and phosphoric 

 acid. The derivation of the first two of these components from 

 proteins and from carbohydrates previously present in the egg is 

 readily conceivable but the question of the origin of the phosphoric 

 acid component suggests several interesting possibilities. In the first 

 place it is evidently not derived from the external medium which 

 bathes the cells, for perfectly normal development will occur in Van 

 t'Hoff 's Solution, which contains no phosphates. The phosphoric acid 

 which is required for the synthesis of nucleins must therefore be derived 

 from some constituent of the egg-cell. Two groups of constituents 

 present themselves as abundant sources of phosphoric acid, namely 

 inorganic phosphate and the Phospholipins, of which egg-lecithin may 

 be taken as a type. Now we have no evidence whatever that nucleic 

 acid can be synthesized directly from inorganic phosphates, but we 

 have, on the contrary, a great deal of evidence which goes to show that 

 phospholipins contribute in the synthesis of nuclear materials. Thus, 

 Miescher has shown that during spermatogenesis in the salmon the 

 " lecithin "-content of the tissues diminishes, Hoppe-Seyler has pointed 

 out that the Lecithin-content of embryonic tissues is exceptionally 

 high and Mesernitzky and Plimmer and Scott and others have shown 

 that the lecithin-content of hen's eggs which is initially very high, 

 progressively diminishes during the development of the embryo. That 

 the same process occurs in the development of the sea-urchin egg 

 has been shown by Robertson and Wasteneys, who estimated the pro- 

 portion of alcohol-soluble phosphorus in eggs which had just been 

 fertilized and again in eggs which had developed to blastulse and plutei. 

 The following were the results obtained with the developing eggs of 

 Strongylocentrotus purpuratus: 



Percentage of the total phosphorus 

 present in alcohol-soluble forms. 



Stage of development. Experiment I. Experiment lI7 



Fertilized eggs . . . . 39.5 46.5 



Blastulse 36.5 38.8 



Plutei 35.2 35.1 



