THE PERMEABILITY OF PROTOPLASM 113 



For each experiment from 100 to 200 discs were cut 

 from the fronds and packed together, like a pile of coins, 

 to form a cylinder 5 to 10 centimetres long and about 

 1-3 centimetres in diameter. These were clamped by a 

 ring of glass rods attached to a block of hard rubber at 

 each end. Each rubber disc carried a platinum electrode, 

 covered with platinum black, against which the algal 

 tissue was pressed by means of a screw. The area of the 

 discs of living cells amounted to from 265 to 530 square 

 centimetres. The measurements of resistance were carried 

 out in the usual manner by means of a Wheatstone bridge, 

 and the figures recorded refer to readings taken between 

 18-0 and 18-2. 



The procedure adopted was to immerse the cylinder in 

 a solution for some time, and then to measure the resis- 

 tance after the apparatus had been removed from the bath 

 and superfluous liquid had been allowed to drain away. 



Repeated determinations upon the same roll of discs 

 immersed in sea-water showed by their consistency that 

 even prolonged treatment did not damage the cells, for 

 further work demonstrated that injury is accompanied by 

 a fall in resistance. 



The resistance of such a cylinder was found in one case 

 to be 1,100 ohms, whereas that of a cylinder of sea-water of 

 equal dimensions was 320 ohms. Thus the additional resis- 

 tance was due to the living protoplasm and walls of the 

 cells, for the salts within the tissue are here closely similar 

 to those of the sea. That the difference was occasioned 

 almost entirely by the living cells is made clear by the 

 fact that when these are killed by a 2 per cent, solution of 

 formalin in sea-water, or by drying carefully, the resistance 

 fell to about 320 ohms. This observation further shows that 

 there is no doubt that the ions, which carry the current, pene- 

 trate more rapidly into dead than into living protoplasm. 



8 



