428 Pruf. Burdon-Sanderson and Mr. F. J. M. Page [Dec. 14, 



We next proceed to compare the effects of single shocks mth that of 

 faradization. The difference is striking. If the same experimental 

 method is emplo3''ed as before, with the exception that each excitation 

 consists of the passage through the tissue not of a single induction-shock, 

 but of a rapid succession of such shocks in alternatel}" opposite directions, 

 it is found that an effect is obtained vdth currents of relatively small 

 intensity, so that if the experiment is begun with the coil at 20 centims. 

 distance, and pushed np a centimeter at a time, the leaf begins to respond 

 after one or two approximations. 



This obseryation appeared to us to indicate plainly that, with relation 

 to stimuli, the excitability of the leaf resembles that of the terminal 

 organs of the higher animals, with reference to which it has been lately 

 ascertained that they can be so excited as to awaken reflexes by relatively 

 feeble electrical stimuli, if applied at very short intervals and repeatedly. 

 We therefore proceeded to make experiments in which each excitation 

 consisted of a definite number of induction- shocks in rapid succession. 

 The results were in accordance with, our expectations. It having been 

 ascertained that with the electrodes in a certain position a single instan- 

 taneous contact had no effect when the secondary coil was at 7 centims., 

 but was followed by an excursion when it was pushed into 6-5 centims., 

 it was set once more at 7 centims. Again a single contact was 

 without result ; two such contacts at ^-second intervals were also 

 futile ; but after 3 contacts there was an excursion. This experiment 

 ha-\dng been several times repeated, the coil was pushed back to 8 centims., 

 and successive experiments were made with, series of 2, 3, and 4 con- 

 tacts at -I- intervals, which were in each case without effect. After 

 5 contacts, however, there was an excursion. On now interposing the 

 vibrator of the induction-apparatus, of which the rate of vibration was 

 30 per second, it was found that an excursion was readily produced at a 

 distance of 11 centims., thus showing that the feebler the excitation 

 the more frequently must it be repeated in order that a result may 

 follow. 



These facts afford the key to the understanding of the phenomena 

 when the leaf is excited at short intervals by faradization, the excitation 

 being continued each time until an excursion is produced. "When this 

 plan is adopted we have the opportunity of observing the combined 

 influence of summation and of gradually increasing exhaustion. At first 

 the leaf responds after eight or ten excitations, and a series of results 

 present themselves quite analogous to those related in the preceding 

 paragraph ; but as the tissue immediately surrounding the electrodes loses 

 its excitability, the number of excitations required to awaken it to action 

 rapidly increases, the effect being postponed for longer and longer 

 periods until it finally fails to occur. 



Thus, in eleven successive series of excitations at oiie-niinute intervals, 



