ELECTROTACTILE DETECTION OE EXCITATORY PULSE 257 



different effects are possible. For example, in the case of 

 muscle with parallel fibres, the wave of excitation will travel 

 onwards from the excited point, the contraction produced 

 giving rise to expansion of the muscle in a direction at right 

 angles to that of propagation. In the intestinal muscle, 

 however, owing to a different distribution of the fibres, the 

 propagated wave is one of constriction. Now, it is clear that 

 these two kinds of muscle, placed within enclosing contacts, 

 will give rise, during the passage of excitatory waves, in the 

 one case to an increase of pressure, and in the other to its 

 diminution. 



We are thus prepared to see that if similar contractile 

 waves pass through a vegetable tissue, they may be detected 

 by means of a concomitant variation of pressure — a variation 

 which may prove to be either an increase, or a diminution, 

 according to the particular disposition of the contractile 

 elements in the tissue. If the tissue, again, should happen to 

 be anisotropic, the same wave of contraction may appear to 

 give rise to a diminution of pressure in one direction, and an 

 increase in that at right angles. In any case the excitatory 

 wave, in the course of its transmission through any given area, 

 might be expected to produce variation of pressure, as between 

 two diametrically opposite leading-points. 



I am now about to describe the electrical device which 

 I have used for the detection of such transient pressure- 

 variations, concomitant to the passage of excitation through 

 vegetable tissues. It is known that the electrical resistance 

 of contact varies with pressure, and on this principle depends 

 the construction of the microphone. But a loose contact, 

 such as would be favourable for microphonic use, is unsuitable 

 for our present purpose, by reason of the disturbance to which 

 it is subject from atmospheric vibration. The necessity to 

 be met, therefore, is that of the adjustment of an electric 

 contact, which shall not be subject to resistance-variation 

 from atmospheric disturbance, and which shall, at the same 

 time, be sensitive to the pressure-variation effected by the 

 excited tissue. 



S 



