314 



ADVENTURES IN RADIOISOTOPE RESEARCH 



We may get some, though very restricted, information by comparing 

 the heavy hydrogen (D) content of the organ phosphatides with that 

 of the organ glycerides. After the lapse of 10 hours, the ratio 



liver phosphatide D kidney phosphatide D 



liver glyceride D 



kidney glyceride D 



where D denotes the relative heavy content of the total "non-exchange- 

 able" hydrogen, was found to be 1 : 2. 



EXPERIMENTAL PROCEDURE 



The labelled phosphate of negUgible weight, dissolved in physiological sodium 

 chloride solution, was injected into the vena jugularis of the rabbit drop by drop 

 during the experiment. Per hour 2.5 ec. were injected; the experiment took usually 



Fig. 1. Change of the specific activity of the plasma inorganic P 

 during continuous intravenous injection of labelled phos- 

 phate to a rabbit. (Specific activity = per cent of the labelled P 

 injected, found in 1 mgm. P). 



4 hours. By taking small samples from the ear vein at different intervals, the 

 change in the activity of the plasma was followed. In several cases, we extracted 

 the inorganic P of the plasma and measured its specific activity (activity per mgm 

 P), in others we contented ourselves with the measurement of the total activity 

 of the plasma which, in experiments of short duration, is solely due to the inorga- 

 nic phosphate present. 



The labelled P was injected drop by drop into the vena jugularis in order to 

 obtaLa a comparatively small and easily accountable change in the activity level 

 of the plasma (see Fig. 1). If aU the labelled P is injected at the start of the experi- 

 ment, as in our early experiments and in all experiments carried out by other 

 workers with labelled P, the activity level of the plasma is very high at the begin- 

 ning, and it is slow at the end of the experiment (see Fig. 2). If the labelled P is 

 given by subcutaneovis injection or by mouth, the activity of the plasma first 

 increases with time and later decreases (see Fig. 3). The sensitiveness of the radio- 



