1018 



ADVENTUKES IX RADIOISOTOPE RESEARCH 



Figure 17 demonstrates the result of the first investigations carried out 

 on the permeabiUty of the capillary wall^^^\ It brought out the very 

 great speed at which ions of the plasma interchange with those of the 

 extra vascular space. In the course of 1 minute half of the sodium atoms 

 originally located in the circulation leave the plasma of the rabbit. In the 

 human organism after the lapse of 18 minutes 80 per cent equipartition 

 of the sodium ions . originally present in the plasma is reached^^"^. 



Min 



YiG. 17. — Rate of extrusion of intravenously injected labelled ions 

 from the circulation of the rabbit, expressed in dilution volume 



of body water. 



In the early experiments which lead to the results seen in Fig. 17, 

 blood samples were taken at intervals and their radioactivity compared. 

 The great progress made in the construction of measuring devices makes 

 it possible today to follow the disappearance of radioactive sodium from 

 the circulation by placing a scintillation counter in the precordial region 

 and to measure activity changes within extremely short time intervals. 

 Our knowledge on the pattern of disappearance has also been much 

 increased since the first investigations were carried out in this field. 

 We know now that the curve representing the distribution and disappear- 

 ance of injected radioactive sodium from the plasma is composed of at 

 least 6 components. The first, very rapid component is followed by a 

 second one which was measured by Strajman and his associates^^^^ 

 in men and women of different ages. Their very instructive results 

 are seen in Fig. 18. With increasing age, presumably due to an increasing 

 arterial sclerose, the distribution of the injected sodium ions in the circula- 

 tion takes place at a decreasing rate. 



