4 I2 



COMPARATIVE ELECTRO-PHYSIOLOGY 



Type I., we may expect to obtain the unmasking of the nega- 

 tive element in the response, as the after-effect, on the with- 

 drawal of stimulus. Here there should be cessation of stimulus 

 at the end of the second phase, in this case, maximum minus. 

 The negative element, thus freed from its opposing positive, 

 will demonstrate its presence by over-shooting in the 



negative direction (fig. 245). This 



is seen in the next two figures 

 (246 and 247). The specimen 

 taken was the petiole of cauli- 

 flower, in that particular condition 

 which gives the positive as its 

 immediate response. The alter- 

 nation of plus-minus-plus-minus, 

 under continuous stimulation, is 

 seen in the first part of fig. 246. 

 Stimulus was now stopped at a 

 point short of the maximum nega- 

 tivity, and we see the consequent 

 overshooting in the negative 

 direction. In the next figure 

 (fig. 247), is seen a single alter- 

 nation of plus-minus during stimu- 

 lus, in a different specimen, with 

 its after-effect and recovery from 

 that effect. The impinging stimu- 



FlG. 245. Diagrammatic Repre- 

 sentation of Phasic Alter- 

 nations and After Effect in 

 Type III. 



During action of light the phasic 

 alternations are a b, b a', 

 a' b', b' a" (+- + -); b is 

 here the maximum positive, 

 and a' the maximum nega- 

 tive. Withdrawal of stimulus 



element, which is exhibited 

 by the overshooting of the 

 curve in the negative direc- 

 tion, a' c. 



at point of reversal a' 



causes unmasking of negative lus was in this second case stopped 



at the exact point of maximum 

 negativity, and the overshooting 

 curve shows, by its abrupt steep- 

 ness, its sudden freedom from the restraint imposed by the 

 opposite element of positivity. Thus, in this instance of 

 Type III., we arrive at the typical formula of ( + - ...). 

 It may then be said that under this head, of alternation of 

 phase, we have examined representative cases of the two ex- 

 treme Types I. and III., between which lie many variations, 

 classified as intermediate, or Type II. 



