THE PERMEABILITY OF PROTOPLASM 115 



1,750 within fifteen minutes, remaining stationary at this 

 for some hours. It then slowly sinks, finally reaching the 

 value of about 320 ohms as in sodium chloride. If replaced 

 in sea-water, soon after the maximum has been reached, 

 the original resistance is regained and maintained un- 

 changed. 



When the two chlorides are combined in the same pro- 

 portions as those in which they are present in sea-water, 

 their antagonistic action is clearly shown. For when 

 placed in such a mixture, diluted till its conductivity was 

 the same as that of sea-water, the Laminaria discs neither 

 gained nor lost in resistance within twenty -four hours. 



Thus it is evident that the presence of a relatively small 

 number of calcium ions greatly delays the penetration of 

 sodium ions. 



Further experiments proved that the chlorides of 

 potassium, magnesium, caesium, rubidium, lithium, and 

 ammonium, also the bromide, iodide, nitrate, sulphate, and 

 acetate of sodium, act in general like the sodium chloride, 

 though with different degrees of rapidity, whereas the 

 chlorides of barium and strontium act like that of calcium. 

 Apparently only the positive ions are effective in these 

 changes. 



With regard to the increase of resistance occasioned by 

 transfer of tissue into calcium solutions two hypotheses 

 have been formed. One regards the plasmatic membrane 

 as unchanged, and explains the increased resistance as due 

 to the protoplasm being normally less permeable to calcium 

 than to sodium ions. 



Certain facts, however, favour the other hypothesis, 

 that the plasmatic membrane itself undergoes an altera- 

 tion as the result of the transfer. Thus Osterhout calls 

 attention to certain changes in the appearance of the 

 protoplasm brought about by calcium solutions. Alum, 



