28 INJUEY, RECOVERY, AND DEATH 



in the new solution, the whole apparatus being moved 

 about in the dish to secure thorough mixing. By means 

 of a medicine dropper the sea water around the platinum 

 electrodes is thoroughly washed out. In some cases 

 it is desirable to transfer to a second dish to ensure 

 against contamination by sea water. 



By this means a very rapid change is effected and, 

 as the disks are thin, diffusion is soon completed (this is 

 often the case in 5 minutes and should not in any event 

 require more than 10 minutes). Since the outward diffu- 

 sion of salts may take place at a different rate from the 

 inward diffusion there may be an apparent rise or fall 

 of resistance in consequence. This effect lasts but a 

 short time and is found in dead as well as in living tissue. 

 It is therefore easy to guard against error due to 

 such causes.^^ 



The resistance of the disks at the ends is much 

 greater than that of those in the middle since the current 

 spreads out after issuing from the small opening,^^ H, 

 in the rubber disk (Fig. 1). For this reason the best 

 disks of tissue should be placed at the ends and their 

 positions should not be changed. Care should be taken 

 that they are not cut or injured by contact with the 

 edges of the opening in the rubber disk.^^ The inequal- 

 ity between the disks at the end and in the center may 

 be minimized by introducing at intervals rubber disks 



"Cf. Osterhout (1918, D) . 



"It results from this that the resistance does not increase in direct 

 proportion to the number of disks. If we plot the resistance aa ordinates 

 and the number of disks as abscissse, we obtain a curve which is concave 

 toward the base line. The curve is approximately logarithmic. 



"These edges may be rounded by filing. A soft rubber disk may be 

 placed between the hard rubber disk and the tissue. 



