RATE OF PENETRATION OF IONS THROUGH THE CAPILLARY WALL 



433 



Permeability of Muscle and Brain Capillaries 



The figures stated in the j)receding section give information on llic 

 rate at which ions and molecules leave the capillary system. Should 

 a minor part of the capillary wall be shghtly permeable or ev(>n imper- 

 meable to some of the substances investigated, this would nol have 

 ])een revealed by the figures given above, since these figures indicate 

 the permeability of the very inhomogeneous capillary system in toto. 

 If we want to know the average permeability of the muscle capillaries, 

 for example, to 24Na, we have to compare the ^^Na content of plasma 

 and muscle samples of known weight. 



The results of such measurements are seen in Table 6, in which the 

 percentage ratio of the ^^Na content of 1 gm fresh gastrocnemius tissue 

 to 1 gm plasma is given. The table contains also data on the ^^P content 

 of muscles and the ^^Na and ^^P content of the brain tissue. After the 

 lapse of 11 min, a proportif)nal partition of ^^Na between plasma and 



T.\BLE 6. — Ratio of the -^Na and ^ap Content, Respectively, of 1 gm Tissue 



A.xD 1 OM Plasma 



Tissue 



Time in min 



Ratio of tlio content of 1 gni 

 tissue and 1 gm plasma x 100 



"X:l 



I 



3!p 



gastrocnemius is nearly reached, since the size of the extracellular space 

 of the gastrocnemius of the rabbit is about 11 per cent of the weight of 

 the muscles. The muscle capillaries are seen to be more permeable to 

 sodium than to phosphate : in the course of the first minute about four 

 times more 24Na left the plasma for the muscle tissue than ^^p. 



The permeability of the brain capillaries to -^Na and also to ^^P is 

 lower than that of the muscle capillaries, those of the white brain sub- 

 stance being apparently less permeable than those of the grey brain 

 substance to 24"Xa^i). After the lapse of 62 hours, we found (Hahx et a7_ 



^1^ This is possibly an expression of the fact that the vascularity of the grey 

 matter greatly exceeds that of the white. 



28 Hevesy 



