436 ADVEXTURES IX RADIOISOTOPE RESEARCH 



located in the interspaces and the rest in the cells. If the extracellular 

 water should alone take part in the exchange process, we should expect 

 in the case of a proportional partition of the heavy water between plasma 

 and extracellular water the ratio of the density excess to be about 7. 

 From the fact that this ratio is found after lapse of 5 min. to be but 

 1.62 we have to conclude that during that time not only a proportional 

 partition of the labelled water between plasma and the extracellular 

 fluid of the muscles took place, but a large part of the cell water was 

 replaced by plasma water as well. 



Summary 



Solutions of labelled chloride, bromide, sodium, potassium, phosphate and 

 deuterium oxyde were injected into the circulation of rabbits and the speed of 

 the escape of the labelled ions from the plasma was determined. Labelled 

 potassium was found to leave the circulation at a faster rate than any other ion 

 investigated. 



Information on the permoabiUty of the muscle and brain capillaries were 

 obtained by comparing the labelled sodium, phosphate and heavy water content 

 of muscle and plasma, respectively brain and plasma. The muscle endothelium 

 w^as found to be more permeable to sodium and to phosphate than the endothelium 

 of the brain. The partition ratio of labelled sodium between plasma and the chlo- 

 ride space of the brain amounts after the lapse of 11 min only to 1/30 of the equi- 

 librium value; during that time ^/^q of a proportional partition of labelled sodium 

 between plasma and the chloride space of the muscle was obtained. 



In the course of an hour, somewhat less than 1/3 of the proportional partition 

 of bromine between plasma and the grey brain substance was reached. Proportional 

 partition of labelled water between plasma and the muscle water was observed 

 after about half an hour. 



References 



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 I. H. E. Griffiths and B. G. Margraith (1939) Nature, 143, 179. 

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 E. P. HiALT (1939) Amer. J. Physiol. 126, 553 

 A. Keys (1937) Proc. Faraday Soc 932. 



A. Krogh (1929) Anatomy and Physiology of the Capillaries, New Haven. 

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