256 



ADVENTURES IN RADIOISOTOPE RESEARCH 



An important objection can, however, be raised to our conclusion! 

 it may be argued that the intestinal tract might contain large amounts 

 of phosphorus other than the labelled phosphate administered by us, 

 the presence of which must be accounted for when carrying out the 

 above calculation. To investigate this point and to ascertain to what 

 extent the labelled phosphorus was resorbed, we killed the dog after the 

 last experiment, the results of which are seen in the table. We washed 

 ihe intestinal tract with water and determined both its total P content 

 and its labelled P content. We found by activity measurements 39.6 

 mgm labelled P and by chemical determination 175 mgm normal P. 

 Within six hours as much as 259.4 mgm of the 300 mgm administered 

 to the dog was thus resorbed. The 135 mgm. non-labelled phosphorus 

 reached the intestine, presumably along with the digestive fluids, so 

 that the 40 mgm labelled P were 'diluted' to 175 mgm. We determined 

 also the total acid-soluble phosphorus content of the intestinal mucose; 

 it was found to amount to about 40 mgm, bringing the above figures 

 up to 215 mgm. But even if we make the assumption that this dilution 

 was present during the whole of the resorption process we should get 

 the result 5.2 x 0.064 = 0.21 mgm per cent lecithin P. while an in- 

 crease of 2 mgm per cent was found in the blood lecithin P. 



It is of interest to compare the labelled P content resorbed with that 

 actually found in the l)lood stream of the dog. Six hours after the beginn- 

 ing of the experiment, as is seen in the table, only 4.6 per cent of the 

 amount resorbed was found. This result illustrates beautifully the great 

 rapidity of the phosphorus exchange in the body. As observed by us in 

 numerous cases, the individual phosphorus atoms present in the blood 

 stream exchange their places rapidly with others present in the different 

 organs. For this reason we can conclude with certainty that during our 

 experiments the ratio labelled phosphorus to ordinary phosphorus must 

 have been appreciably higher in the intestinal mucose than in the blood. 



The only moderate increase in labelled phosphorus in the blood leci- 

 1 hin after administration of oil, an increase which nevertheless in all 

 our experiments exceeds the increase observed after the radioactive 



