694 COMPARATIVE ELECTRO-PHYSIOLOGY 



three distinct methods. I found that torsional to-and-fro 

 vibration constituted an effective form of stimulus, the 

 amplitude of which could be increased by increasing the 

 angle of vibration. The intensity of stimulus was found 

 to remain constant so long as the period and amplitude 

 vibration were kept constant. The tissue, moreover, was 

 not subject to injury by the use, within limits, of this method 

 (p. 31). My second method was that of Rotary Mechanical 

 Stimulation, in which friction of the terminal area of a pumice- 

 stone electrode constituted the stimulus, whose intensity was 

 determined by the number of rotations (p. 291). The third 

 non-electrical mode of stimulation employed was that of 

 thermal shocks. The area to be stimulated was, in this case, 

 enclosed within a thermal loop of platinum or german-silver 

 wire, the requisite thermal variation being produced by the 

 passage of a heating electrical current round the loop. The 

 intensity of the stimulus could in this case be varied by 

 increasing the intensity or duration of the heating current 

 (p. 38). And finally I have shown that the drawbacks inci- 

 dental to the electrical mode of stimulation might be over- 

 come by the use of equi-alternating shocks, the indefinite 

 polarisation factor being thus neutralised (p. 251). 



As the intensity of stimulus is gradually increased, it 

 is found that the amplitude of response reaches a limit. 

 Beyond this, increase of stimulus evokes no increase of 

 response. On the application of a very strong stimulus, 

 hen, there is an amount of energy which is unable to 

 ind expression in the single response given by the tissue. 

 Under such circumstances, the excess of energy is held 

 atent, and often finds responsive expression later in a 

 series of multiple responses. This phenomenon of multiple 

 response to a single strong stimulus I find to be of very 

 extensive occurrence. As examples of the different kinds of 

 tissues in which this may be observed, may be mentioned 

 the stems and petioles of various plants (fig. 138), the 

 digesting leaves of Drosera (fig. 209), the pitcher of Nepenthe 



