ELECTROLYTIC ACTION 95 



may be moved further and further apart. This can best be shown by 

 applying the single induction shock produced on breaking the circuit. 

 Above 40 C. a stronger shock is usually required, that is the sensitivity 

 is decreased, and the latent period of recovery becomes longer. Below 

 15 C. an increased stimulus is also required, and the latent period of 

 recovery at 5 C. to 10 C. is usually much longer than at 15 C. to 25 C. 



In addition to the latent period of recovery, there is also a latent period 

 of response between the application of the stimulus and the stoppage of 

 streaming, however powerful the former may be. This latent period of 

 response varies from one-half to ten seconds or even more, and is influenced 

 by (i) the age, condition, and size of the cell ; (2) its previous treatment ; 

 (3) the temperature. It is longer in old, large, well-nourished cells, and 

 it is shortened by rises of temperature up to but not above 36 to 40 C., by 

 slight starvation, and by previous sub-maximal stimulation. 



SECTION 42. Electrolytic Action. 



After strong induction currents have been passed for a short time 

 through a cell of Nitella or Chara laid across platinum electrodes, a 

 browning of the cell-wall is often observable, especially near to the positive 

 electrode. This may appear before or after the cell has been killed and 

 streaming has ceased. It is an electrolytic effect due to the algebraic 

 sum of the stronger 'break' shocks ( + ), and the weaker 'make' ones (), 

 being a positive quantity. If, however, the induced currents at ' make ' and 

 ' break ' are nearly equalized by using the Helmholtz side-wire arrange- 

 ment, no such effect is produced, even when the primary current is increased 

 so as to give approximately the same strength to the secondary currents. 



The electrolytic effects of constant currents have been frequently 

 described (cf. Kiihne, 1. c.), and they form a very disturbing factor in 

 prolonged experiments upon excitability. The fatal action of weak but 

 prolonged currents is almost entirely due to their disorganizing electrolytic 

 action upon the protoplasm, and Klemm (1. c., pp. 56-62) has shown that 

 various solid constituents both of the nucleus and of the cytoplasm are 

 rendered soluble. This causes both these structures to swell and become 

 highly vacuolated. For such action a certain voltage is essential, but 

 a current small in quantity needs only to act for a longer time to produce 

 the same total effect as a stronger one of limited duration. The injurious 

 action is less pronounced when the effect of external electrolysis is 

 eliminated by separating the cell from each electrode either by an inter- 

 vening cell or by a few millimetres of water. The internal electrolytic 

 effect can, however, only be suppressed by the use of alternating currents 

 of equal strength, for the cell is composed of substances having dissimilar 

 electro-motive and electrolytic properties. 



