398 



COMPARATIVE ELECTRO-PHYSIOLOGY 



from the photographic record (fig. 234) that this gave rise 

 electrically to an increasing positive effect at the diametrically 

 opposite point. This clearly shows that the latter under- 

 went a positive turgidity variation, in consequence of the 

 forcing-in of water expelled by excitatory contraction from the 

 upper side. It is at this stage the indirect and not the true 

 excitatory effect of stimulus that is being transmitted to B. 



By this experiment it is 

 also demonstrated that the 

 positive curvature induced 

 by the unilateral applica- 

 tion of any stimulus is the 

 joint effect of the direct 

 excitatory contraction of 

 the proximal side and the 

 indirect or hydro-positive 

 expansion of the distal. 1 

 Another interesting 



FIG. 234. Record of Response to Moderate , , , 



Unilateral Stimulation under the Experi- Phenomenon to be Ob- 



mental Arrangement described served in this curve is that, 



Response of distal point by increased ft ^ maximum effect 



galvanometric positivity due to hydro- aiier 



positive effect. Note initiation of multi- has been reached, there 



pie response. . . r .,, , 



is a series of oscillatory 



multiple responses. In this result there may possibly be two 

 factors in operation : first, after the maximum hydro-positive 

 tension has been set up there may be a gradual percolation 

 of the true excitatory effect, with its opposite reaction, the 

 unstable balance thus produced manifesting itself in oscilla- 

 tions ; and, secondly, we know that increased hydrostatic 

 tension has the effect of initiating multiple responses, as seen 



1 In records of such a response as I have just described, when exhibited by 

 highly excitable tissues, a preliminary negative twitch, of momentary duration, 

 may sometimes be observed. This is not due to the conduction of true excitation, 

 but to pseudo-conduction. The sudden blow delivered by the hydrostatic wave 

 on its arrival at the distal point is, in a highly excitable structure, sufficient of 

 itself to induce a short-lived excitatory effect. Thus this does not represent the 

 true transmission of excitation, but its initiation de novo by a secondary mecha- 

 nical cause (p. 446). 



