CURRENT OF INJURY AND NEGATIVE VARIATION 153 



We shall now, however, take an instance in which excitation 

 is transmitted and observe the persistent negative after-effect, 

 due to strong stimulation. We know that a cut (mechanical 

 section) or the application of a hot wire (thermal section) 

 acts as a strong stimulus, and the effective intensity of such 

 stimulation will obviously decrease with increasing distance 

 from the point of stimulation. Hence, if we observe the 

 persistent excitatory change of galvanometric negativity, 

 which is induced as between an indifferent point say, the 

 surface of a leaf and points increasingly near to the zone 

 of section, we shall find that the electro-motive change 

 is greatest at the point of section, and is progressively 

 lessened as we recede from it. This induction may be 

 verified experimentally by taking readings of the persistent 

 negativity, as between an indifferent point, B, and points 

 such as the contacts a, b, c, d, A (fig. 107), which are further 

 and further removed from the point of section. For this 

 purpose we may employ a capillary electrometer, whose indica- 

 tions are independent of the varying resistance of the interposed 

 tissue. The magnifying power of the observing microscope 

 was so adjusted that 'i volt gave a reading of 100 divisions 

 of the micrometer. In carrying out an experiment on the 

 leaf of Colocasia I found the electrical distribution, as between 

 an indifferent point on the lamina and points on the 

 sectioned petiole, at increasing distances from the section, 

 to be as shown in the following table : 



TABLE SHOWING ELECTRICAL DISTRIBUTION IN SPECIMEN OF Cclocasia. 

 [The sectioned end was negative. 100 divisions = -I volt.] 



It will thus be seen that points near the sectioned end are 

 more negative than others further away. 



