ORIGIN OF PHOSPHORUS COMPOUNDS IN HENS' EGGS 



289 



Table 14. — Ratio of the Specific Activity of Egg P and 



SoLTTIOX P 



DISCUSSION 



We saw that by investigating the labelled phosphorus content of 

 eggs or yolks we could draw conclusions as to the growth of the egg 

 or yolk since the date of administration of the labelled P. It is, for 

 example, possible to show that while the egg is in the oviduct not only 

 is no more yolk formed but also no new lecithin molecules are synthetised. 

 Should suitable enzymes be present, new and thus labelled lecithin 

 molecules could be formed without any growth of the yolk. The ovary 

 of a laying hen contains numerous tiny yolks growing at a slow rate; 

 by comparing the incorporation of labelled P by such yolks, we get 

 a quantitative measure of their relative growth since the administration 

 of the labelled P. When comparing the growth of small yolks with 

 large ones we can usually not obtain strictly quantitative results as 

 to the relative growth because of the much more rapid relative growth 

 of large yolks compared with that of small ones. 



Placing eggs in a solution containing labelled P for some days we 

 find the shell to contain an appreciable part of labelled P, while the 

 amount shown by the white and especially by the yolk is very small, 

 though easily measureable, even in the case of the yolk. No formation 

 of labelled lecithin is, however, found in the yolk. 



As to the formation of lecithin in the growing yolk, we arrive at the 

 following result: The phosphatides found in the yolk are synthetised 

 at least to a large extent in the liver and are transported through the 

 plasma to the ovary which extracts the phosphatides. This is most 

 clearly seen in the experiment in which the hen was killed only 5 hours 

 after the administration of the labelled sodium phosphate. In this experi- 

 ment the specific activity of the liver phosphatide P reached 54% of 



19 Hevesy 



