434 ADVENTURES IN RADIOISOTOPE RESEARCH 



1939) the 24Na content of 1 gm brain to make out 32 percent of that 

 of 1 gm plasma, a figure which corresponds to that stated (Manery 

 and Hastings, 1939) for the sodium space of the brain. 



Manery and Bale (1939) carried out experiments with labelled 

 sodium and phosphorus. They state that, in the course of an hour, 

 the 24Na uptake by the brain and the sciatic nerve is much smaller than 

 to be expected in the case of a proportional partition of ^^Na between 

 plasma and interspaces of these organs while, in the case of the other 

 organs, such a partition was reached after the lapse of 20 min. Wallace 

 and Brodie (1937,1939) investigated the distribution of iodide, thio- 

 cyanate and chloride in various tissues of the body and found that the 

 relative concentration in terms of blood tissue ration was alike for the 

 three substances in the organs examined, with the exception of the 

 brain in which the chloride was in much larger amounts that the other 

 two. In a later investigation (1939) these authors found that these anions 

 distribute in the central nervous system in the same ratio to chloride 

 as in spinal fluid, whereas in other body tissue they distribute in the 

 same ratio to chloride as in serum. That sulphate passes more slowly 

 than bromide or nitrate through the brain capillaries can be concluded 

 from experiments in which the chloride content of the plasma was 

 replaced by sulphate (Amberson et at. 1938), bromide (Weir 1936), 

 and nitrate (Hialt 1939), respectively. 



We compared, furthermore, the activity of 1 gm of the grey brain 

 substance with that of 1 gm plasma 59 min after the administration 

 of radiobromide. The ratio found was 9.3 per cent. As the chlorine space 

 of the brain tissue of the rabbit is 35 per cent, we have to follow that in 

 the course ofan hour, less than 1/3 of the proportional partition of bromine 

 between plasma and the extracellular volume of the brain is obtained. 



Permeability to Water 



We investigated previously the rate at which heavy water introduced 

 into the circulation leaves the plasma (Hevesy and Jacobsen, 1940). 

 These measurements were extended by determining the distribution of 

 labelled water between plasma and gastrocnemius of equal weight. The 

 figures obtained are seen in Table 7. The water content of the samples 

 was driven off and was collected in vacuo as described previously. We 

 are much indebted to Miss Hilde Levi for kindly determining the 

 density of the water samples obtained by making use of Linderstrom- 

 Lang's floating drop method. 



The density excess of these water samples over the density of normal 

 body water is a measure of their labelled water content. The ratio of 

 the density excess of plasma water and muscle water is stated in Table 7 

 and Figure 3. 



