252 ADVENTURES IN RADIOISOTOPE RBSBARiClH 



of blood with an inorganic phosphorus content of 4.5 mgm per 100 

 cc, 0.75 mgm of phosphorus; if we inject radioactive phosphorus 

 (1000 units) of negligible weight, 1 activity unit will indicate 0.75/1000 

 mgm of the phosphorus originally present in the plasma. In the 

 blood plasma, however, numerous fast processes take place in which 

 the phosphorus atoms are involved; this is shown by investigations 

 carried out with labelled P. We get beside other reactions, a partition 

 of the phosphate ions between the plasma and the phosphate in the 

 skeleton, and in view of the very large preponderance of the latter a large 

 part of the labelled phosphate ions will soon be present in the skeleton. 

 Sim.ilar considerations apply to the muscles and other organs. The com- 

 paratively large amount of phosphorus ester present in the blood cor- 

 puscles will also take part in a dynamic interchange with the labelled 

 phosphorus atoms present in the plasma. In the course of the last two 

 years Prof. E. Lundsgaard and one of us have carried out and extended 

 investigation of this point, to be published shortly. As a result of the 

 processes just mentioned, only a few, let us say 10, units remain behind 

 of the 1000 activity units introduced into the plasma, while the total 

 inorganic phosphorus content of the plasma is unchanged and amounts 

 as before to 0.75 mgm. The effect will be that 1 activity unit will now 

 indicate as much as 0.75/10 mgm (i.e. much more) phosphorus. On 

 account of the rapid dynamic happenings in the animal body our scale 

 of indication will rapidly change and, the function representing this 

 change being a very intricate one. One way to obtain some infor- 

 mation is the following. We make an experiment of very short du- 

 ration in which 1 activity unit does actually indicate 0.75/1000 

 mgm of labelled phosphorus; then we make a longer experiment and 

 determine experimentally the activity of the inorganic phosphorus 

 present in the plasma. If only 10 activity units are now present then 

 1 activity unit indicates 0.75/10 mgm P at the latter stage. The activity 

 accumulated at the early stage will be correctly interpreted by making 

 use of the first mentioned scale, that accumulated at the last stage 

 by making use of the last mentioned scale. In some cases we have followed 

 the labelled P content of the blood continuously. Let us now consider 

 the rat killed after 1 hour, the blood plasma of the animal containing 

 0.75 mgm inorganic phosphorus, a 4.2 • lO^^th part i.e. 3.2 • 10"^ mgm of 

 this was converted into brain lecithin phosphorus. This being a very 

 small part of the brain lecithin phosphorus, the reverse reaction can bo 

 disregarded and the amount of labelled brain lecithin phosphorus 

 formed in 100 hours can be taken as a hundred times as much, i.e. 3.2- 10"^ 

 mgm i.e. 8 mgm of the brain lecithin is newly formed in the course 

 of about 4 clays. The calculation of the weight of labelled phosphorus 

 was carried out on the basis of an analysis of the activity of the blood 

 and of the brain lecithin after the lapse of one hour. Now one part of 



