RESPONSE OF EPITHELIUM AND GLANDS 317 



direction as the so-called current of rest, constituting a 

 positive variation of it. 



From these experiments it is clear that the responsive 

 current is due to the greater intensity of the induced gal- 

 vanometric negativity at the more excitable glandular 

 surface. It must, however, be noted here that this definite 

 understanding of the phenomenon has been arrived at by 

 fixing our attention on the relative excitatory reactions at 

 the two contacts. If, instead of this, we had regarded it from 

 the usual point of view, of variations of the resting-current 

 only, we must have interpreted it as apparently an abnormal 

 positive variation ; l for the so-called resting-current, in such 

 a case, on account of the excitatory after-effect of injury, 

 must also, as we have seen, flow from the more excited gland 

 to the less excited muscle. Great confusion, and resultant 

 misinterpretation of observations, have arisen from not 

 sufficiently recognising these facts, that the resting-current 

 may be originated in either of two distinct ways, and that 

 the excitatory effect may consequently be summated with 

 it in different manners. The resting-current in the primary 

 condition is, as I have demonstrated elsewhere, the natural 

 current. This originates in the natural differences of ex- 

 citability between different points, and is, in the intact 

 specimen, through the tissue from the less to the more ex- 

 citable. External stimulus now gives rise to a responsive 

 current, which is in the opposite direction, and therefore 

 constitutes a negative variation of this. This takes place 

 because the more excitable point, which was naturally 

 positive, has now become negative. But we may have a 

 current of rest which is due to previous excitation, or 

 injury, such as may be caused by the shock of the pre- 

 paration. This current, though usually regarded as the 

 resting-current, is not the true natural current of rest. It 

 is really, as it were, the responsive current become persis- 

 tent. Succeeding stimuli, inducing responsive galvanometric 



1 We shall find in Chapter XXVII. that similar misinterpretations have arisen 

 with regard to the responsive current in the retina, p. 417. 



