"K LABELLED EED CORPUSCLES IN BLOOD VOLUME MEASUREMENTS 577 



and also the percentage of ^-K which leaves the corpuscles during a 



given time. 



From the fact that after the lapse of 15 minutes 1 gm of red corpuscles 



was found to contain 0.205 times as much ^^K as did 1 gm of plasma and 



100 gm of blood to contain 40.1 gm of red corpuscles follows that, out of 



100 counts added to the plasma 12 penetrated into the erythrocytes. 



As the potassium content of the plasma amounted to 17.8 mgm % it 



follows that 12% of 10.7 mgm = 1.28 mgm of those potassium atoms, which 



were in the plasma at the start of the experiment, are found 15 minutes 



later in the corpuscles, and vice versa. When making this statement we 



failed to consider the increase in sensitivity of the radioactive indicator 



in the course of the experiment. The plasma activity decreased during 



the experiment, took 15 minutes from 100 to 88.0, and correspondingly 



its mean value during the experiment was 94.0. From these figures 



it follows that the amount of potassium which interchanges between 



plasma and red corpuscles in the course of 15 minutes is not 1.28 mgm 



1.28 



but = 1.36 mgm. 



0.94 



As the red corpuscles contained 325 mgm % potassium, thus those 

 present in 100 ml of blood 130 mgm the 1.36 mgm of potassium, which 

 move from the corpuscles into the plasma in the course of 15 minutes 

 amounts to 1.0 % of the potassium content of the erythrocytes. If we 

 inject labelled erythrocytes into the circulation we can thus expect that 

 1.0% of their ^^K content is given off to the plasma in the course of the 

 first 15 minutes. 



The loss of *^K by the active corpuscles when introduced into an 

 inactive circulation can thus be expected to be smaller than the loss of 

 radiophosphorus by ^^p labelled corpuscles during the same time. Reeve 

 (1949); Nylin (1951). This conclusion is borne out by the results of 

 experiments in which 42K labelled blood or red corpuscles were injected 

 Into the circulation and are demonstrated in Figs. 1 and 2. After injecting 

 labelled blood into the circulation, the activity of the red corpuscles 

 seems to remain unchanged during 1 hr within the error of the method, 

 which amounts to about 3 %. Injection of labelled red corpuscles is 

 followed by an initial loss of about 2 % of their ^^j^ content, followed by 

 a further loss of 5 % in the course of the first 2 hours. As we found a loss 

 of 43 % in the course of 24 hours, the mean loss of ^^K by the labelled 

 erythrocytes per hour works out to be 2.1 %, a figure almost identical 

 with that found by Sheppard and slightly larger only than the new 

 figure found byRAKKER in in t^iYro experiments. That no perceptible loss 

 of ^^K by the erythrocytes was observed following injection of labelled 

 whole blood may be due to an entrance of ^^K from the labelled plasma 

 into the unlabelled corpuscles, which may compensate slight losses of 

 •*2K by the red corpuscles. 



37 Hevesy 



