FORMATION OF PHOSrHATIDES IX THE BI5AIN TISSTK OF ADULT ANIMALS 251 



RELATIVE ABUNDANCE OF LABELLED PHOSPHORUS IN THE BR4IN 

 COMPARED WITH THE AMOUNT PRESENT IN OTHER ORGANS 



The relative abundance of labelled phospliorus in different organs 

 (activity per mgm phospliorus) is seen from Table 5. 



Tahlk .") 



Aiiiinal 



K'iUiMl after 



Total Bi-aii 

 (A) 



liraiii 



liecithiu 



(B) 



Bone 



Rat 5 days 



Rat 3 days 



Rat 1 hour 



Mouse j 21 days 



Rabbit I 27 days 



2.12 

 2.12 

 2.12 



0.94 

 fi.lO 



2.34 

 2.10 

 0.40 

 1.08 

 6.10 



0.9 

 1.0 

 .5.3 

 0.9 

 1.0 



1 (tibial 



1 



1 „ 



1 ,r 



1—3.5* 



* 1 = Tibia diaphysis, 2.6 = Jaw, 3.5 = Tibia epipliysis. 



As is seen from the above figures the ratio between labelled phosphorus 

 in the whole brain and labelled phosphorus in brain lecithin shifts in 

 favour of the latter with increasing time; furthermore that the percent- 

 age replacement of phosphorus atoms in the brain by labelled phosphorus 

 atoms is not very different from that found in the case of the phosphorus 

 atoms of the bone. 



Note added in proof : Professors Artom, Perrier, Sarsana. 

 Santagello and Segre most kindly sent us a manuscript of a paper 

 in which the formation of lipidic phosphorus in different organs has 

 been demonstrated by using radioactive phosphorus as indicator. They 

 found the most marked metabolism in the liver, the intestinal mucosa 

 and the kidney, the least in the brain and the muscles. 



WEIGHT OF THE NE\> LY FORMED LECITHIN 



So far we have only calcula1(>d lecithin phosphorus formed as a per- 

 centage fraction of the total activity given to the animal. In what 

 follows, we will try to calculate the amount of newly formed labelled 

 lecithin in grams. This is a more difficult problem. If we inject 1 mgm 

 of phosphorus showing an activity of 1000 units we know that lh(> 

 presence of 1 unit of activity indicates Vioon "^g"^ o^ ^^^^ phosphorus 

 atoms injected. Now in the blood plasma of a rat we have for 17 cc. 



