RELATIONSHIP OF PHOSPHOLIPINS TO SYNTHESIS 465 



It is evident that the immersion of the blastulae for twenty-four hours 

 in a 0.15 per cent, solution of lecithin enormously retards their develop- 

 ment. Especially remarkable is the fact that after development has 

 actually proceeded to the gastrula stage it shows a tendency to undergo 

 reversion, retracing the course of development to the blastula stage. 



If purpuratus eggs are fertilized by sperm in more dilute solutions of 

 lecithin in sea- water (0.003 per cent, to 0.015 per cent.) the fertilization- 

 membranes are not dissolved sufficiently rapidly to affect development. 

 In these solutions, as has been stated, development is not appreciably 

 retarded until the blastula stage is reached, probably for the reason 

 that colloids cannot traverse the fertilization membrane, and hence 

 the lecithin cannot penetrate the cells of the embryo until the fertiliza- 

 tion membrane has been ruptured. Thereafter development is very 

 markedly retarded and the retardation is greater the greater the con- 

 centration of the lecithin. The eggs are not injured by the lecithin, 

 however, as they will ultimately develop to normal plutei if left in 

 these solutions for a sufficient length of time. 



The action of Cholesterol is so very generally antagonistic to that of 

 lecithin that one might anticipate tjiat it would, as in fact it does, 

 antagonize the effects of lecithin upon the development of sea-urchin 

 eggs. If cholesterol, suspended in a mixture of T ^ sodium oleate 

 and sodium chloride be mixed with lecithin in equal proportions 

 the retarding action of the lecithin upon the development of sea- 

 urchin eggs is almost completely neutralized. The slight retardation 

 which is observed in these mixtures may be due to the Sodium Oleate 

 which is employed to keep the cholesterol in suspension, since sodium 

 oleate is very toxic for sea-urchin eggs and embryos. 



Cholesterol itself, when added to sea-water, has no influence upon 

 the rate of development of the eggs. The emulsions of cholesterol 

 are, however, coagulated by the salts in sea-water and the cholesterol 

 is completely thrown out of suspension in the form of coarse flocculi. 



Since the preparations of "lecithin" employed in these experiments 

 simply consisted of the mixture of phospholipins which is thrown out 

 of an ether extract of egg-yolks by the addition of acetone, it cannot 

 be definitely decided whether the effects observed were in reality due 

 to lecithin or possibly to some other Phospholipin present as an admix- 

 ture in these preparations. The significant feature of these results 

 lies, however, in the fact that if the phospholipins within the egg itself 

 and in other developing tissues behave similarly to the "lecithin" 

 from yolks of eggs, then their progressive disappearance during nuclear 

 synthesis must result in a proportionate diminution of their retarding 

 effect, so that the auto-acceleration of nuclear synthesis, alluded to 

 above, may wholly or in part be due to the consumption of phospho- 

 lipins which is incidental to the process; progressive removal of a 

 retarder being, of course, equivalent in its effect to the progressive 

 addition of a catalyzer. 



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