286 ADVENTURES IN RADIOISOTOPE RESEARCH 



from the comparison of the specific activities of the phosphatide P and the 

 inorganic P as to what extent the phospliatide molecules got labelled we are 

 apt to get values which are possibly too high. A trustworthy value could be 

 obtained by keeping the specific activity of the inorganic P of the plasma 

 constant by continuous injection of labelled phosphate of varying concentration 

 and by thus avoiding a decrease in the specific activity of the inorganic P 

 of the plasma, which is used for the synthesis of the phosphatide molecules 

 in the liver and elsewhere. In the above case we can, however, conclude that 

 a very appreciable part of the liver phosphatide molecules most have been re- 

 newed within the 28 hours of the experiment. In experiments on isolated livers 

 in which the skeleton and other organs are not present it is easy to calculate 

 from the ratio of the specific activities of inorganic P and phosphatide P the 

 amount of newly formed phosphatides. In an isolated liver of a cat in the 

 course of 2.5 hours about 1% of the phosphatide molec-ules present are newly 

 formed. If in the course of 2.5 hours in an isolated liver of a cat about 1% 

 of the phosphatide content is renewed there can be hardly any doubt that in 

 the liver of a living hen in the course of 28 hours a large part of the phos- 

 phatide found is synthetised during that interval: in the liver of a living animal 

 the enzymatic and other actions necessary for the synthesis of phosphatides 

 are certainly as abundant as in an isolated liver and the phosphatide formation 

 in the liver of a laying hen could hardly be less than in that of a cat. We are led 

 to the same conclusion by the following consideration. The daily amount of phos- 

 phatide P tranfered from the plasma into the ovary is, in the case of the hen in 

 qviestion, which was lading one egg every other day, about 50 mgm. The main 

 source of phosphatide production is, as we wiU see, the Uver, and an amount 

 not very far from 60 mgm must therefore have been produced daily in the hver 

 of the hen. Since the latter containing 38 mgm of phosphatide P, a large amount 

 of the liver phosphatide must have been renewed during the experiment. A similar 

 conclusion applies to the plasma phosphatides, the 50 mgm phosphatide P being- 

 carried by the plasma, the total content of which is 20 mgm, the plasma phospha- 

 tide molecules must have been renewed repeatedly. 



We are thus led to the result that the main source of phosphatides in a laying- 

 hen is the liver and that more than one half of the phosphatide molecules present 

 in the hens liver were newly formed during the 28 hours preceding the admini- 

 stration of labelled phosphate. That the greatest part of the phosphatides is formed 

 in the liver of a laying hen and reach the ovary through the plasma is very clearly 

 shown in an experiment in which the hen was killetl only 5 hours after admi- 

 nistration of the labelled phosphate. 



The acid soluble P of the liver, other than inorganic, mainly derived from P 

 ester, shows, as seen in Table 11, a higher specific activity than the phosphatide 

 P present in the liver. 



Experiment on a hen killed after five hours 



3.8 cc. of physiological sodium chloride solution containing 10 mgm labelled 

 sodium phosphate were injected subcutaneously into a hen which weighed 1800 

 gms. The hen, which layed previously one egg daily weighing about 45 gm was 

 kiUed after the lapse of 5 hours. The results obtained are seen in Table 12. Two 

 separate determinations were carried out, the values found and also their 

 average are given. 



As seen from Table 12 the specific acti\ity of the phosphatide P, which is a 

 measure of newly formed phosphatides, is by far the greatest in the liver and 

 markedly higher than that of the plasma phosphatide P. Contrary to the 28 hour 



