THE NATURAL CURRENT AND ITS VARIATIONS 127 



similar to the first. But after this, owing to the greater 

 fatigue with loss of excitability induced in the lower half of 

 the pulvinus, the succeeding responses are seen to be reversed, 

 the responsive current being henceforth from above to below. 



From the table given on the previous page, it will be 

 seen that hardly could any standard have been devised for 

 the study of excitatory reaction, so likely to be prolific of 

 confusion as this, of the so called variation of the resting- 

 current. For in the first 

 three cases displayed, we 

 see one identical excitatory 

 effect, appearing now as a 

 negative, again as doubtful, 

 and a third time as a positive 

 variation of the current of 

 rest. In the fourth case, 

 again, it is actually the 

 abnormal response which 

 appears as the normal nega- 

 tive variation ! But while 

 these responses appear to 

 be so various, the underlying 

 reaction is nevertheless con- 

 stant. The direction of the 

 responsive current is always 

 from the more to the less 

 excited. 



It has thus been shown 



in the course of the present chapter that under normal 

 conditions the current of rest flows in the tissue from 

 the less to the more excitable ; that increase of internal 

 energy causes a positive variation of the current of rest ; 

 while its diminution gives rise to a negative variation ; that 

 reagents which increase excitability induce a positive, and 

 those which cause excitation a negative, variation of the 

 resting-current ; and, finally, that external stimulus induces 

 a negative variation of the resting-current. While these are 



FIG. 88. Variation of the Transverse 

 Natural and Responsive Currents in 

 Pulvinus of Mimosa 



Natural current 4, which is normally 

 down, reversed in consequence of 

 strong external stimulus. The first 

 two responses are normal, i.e. current 

 being from below to above. Strong 

 stimulus is here seen to induce mul- 

 tiple responses. After the second 

 response on account of the greater 

 fatigue induced in the lower half of 

 the pulvinus, the direction of the 

 responsive current is seen to be 

 reversed. Thick dots represent 

 moment of application of stimulus. 



