KATE OF PEXETRATIOX OF lOXS THllOUGH THE CAPILLAKV WALL 



431 



Table 4. — Rate of Disappkahance of ^-K fkom the Cikcu- 

 I.ATION of Rabbits Weighing 2.5, 2.4 and 2.3 kgm, Respectively 



only, larger amounts of potassium than of sodium, chlorine, or bromine 

 are lost by the plasma, requires possibly another explanation. After such 

 a short time the volume of the diluting fluid is much smaller than the 

 extracellular space of the rabbit and the additional outlet can possibly not 

 play a decisive role. The very rapid disappearance of potassium from the 

 circulation suggests the assumption that potassium, when passing the 

 endothelium, encounters appreciably less resistance than does sodium 

 or chlorine. The diffusion constant of potassium in water is larger than 

 that of sodium ; taking the former to be 1, the diffusion constant of 

 sodium makes out 0.65. The diffusion constants of potassium and chlorine 

 are practically identical. The rates of penetration of potassium and 

 chlorine through the endothelium, however, differ greatly. The diffusion 

 rate for water in water was found, using heavy water as an indicator, 

 to be only 1.6 times larger, than that of chlorine or potassium, while 

 the rate of passage of water through the endothelium is very much 

 faster than that of any other substance investigated by us. In the course 

 of 21 sec the labelled water introduced into the circulation of the rabbit 

 is found to be distributed in 506 cc. body water, corresponding to 34 

 percent of the rabbit's weight. 



