26 INJURY, RECOVERY, AND DEATH 



from this the disks are transferred to the support G, 

 which is submerged in sea water. They are arranged 

 inside the glass rods by means of forceps, and care is 

 taken to see that no bubbles of air are caught in the 

 space around the electrode or in the opening at H. 



When the effect of a number of different solutions is 

 to be compared the following procedure is adopted. 

 If there are seven solutions seven disks are cut from 

 the same part of a frond: each disk is placed in a 

 separate tumbler of sea water. A second lot of seven 

 disks is cut, as close to each other as possible, and 

 placed in the tumblers, so that each tumbler contains 

 two disks. This is continued until each tumbler con- 

 tains one hundred disks. By this means the material 

 in the different tumblers is made as similar as possible. 

 The disks in each tumbler are then packed together 

 (like a roll of coins) to form a cylinder whose resistance 

 is measured. Throughout the experiments the differ- 

 ent lots are kept side by side and treated as nearly 

 alike as possible, except that they are placed in dif- 

 ferent solutions. 



The electrode holders are now pressed against the 

 ends of the roll of disks, the block, M, is firmly fastened 

 by means of the set screw, N, and the screw, F, is turned 

 until the electrode holders are tightly clamped against 

 the roll of disks. The pressure used in this operation 

 should be fairly uniform.* 



The apparatus is now lifted out of the sea water'' 



' It was at first thought necessary to use a dynamometer, but it was 

 found that the operator soon becomes so proficient as to make it un- 

 necessary. The resistance is very little affected by variations in pressure. 



' In the earlier experiments the resistance was taken with the cylinder 

 submerged in sea water, and this may be preferable in special cases. 



