MEASURING ELECTEICAL CONDUCTIVITY 25 



(arranged in a circle as shown in the figure) each of 

 which receives the end of a glass rod about 9 inches long, 

 the other end of each rod being fastened in a similar 

 support. The circle (dotted line) just inside the seven 

 small circles represents a disk of tissue inserted between 

 the glass rods with its surface at right angles to them. 

 The smaller circle, E, in the centre 

 represents an opening in the electrode 

 holder through which the current 

 passes from the platinum electrode to 

 the disks of Laminaria. The arrange- 

 ment is shown in Pig. 3, where H 

 represents the opening and L repre- 

 sents the disks. Before reaching the 

 disks the current passes through K, 

 (Fig. 3), a hard rubber disk (with an 

 opening in the centre) which provides 

 mechanical support for the tissue. 



The disks are cut from the fronds 

 by means of a cork borer and have ^.■'seenT^mlh^eXre?-' 

 about the diameter and thickness of a w£ch^°are*Bet"3a9s^rods 



• 1 . rni 1 -I 1 (eeen in section, as a series 



silver quarter. They are packed to- of circles) which hoid 

 gether like a roll of coins (about 100 tissue (seen in'wioni as a 



° ^ dotted hne). 



in all). They are firmly held m 

 place by the glass rods which surround them and by 

 the electrodie holders which press against them at either 

 end. At the same time the spaces between the glass 

 rods allow free circulation of liquid. 



Each disk is placed in sea water as soon as it is cut' ; 



•It was at first thought that cutting might injure the tisaues at the 

 edge of the disk sufficiently to interfere with the results, but experiments 

 proved that this is not the case. Not only do the cells adjoining the cut 

 surface live as long as those in the centre of the disk, but it is found that 

 experiments (made by another method) on intact fronds give the same 

 results as experiments on tjie cut djsks, 



