344 COMPARATIVE ELECTRO-PHYSIOLOGY 



muscular coats of the stomach. From this it was supposed, 

 as we have seen, that the mucous coat of the stomach of the 

 frog had the same electro-motive reaction as its outer skin. 

 We shall find, however, that there is in reality no such 

 similarity between the two, inasmuch as, while the excitatory 

 reaction makes the outer skin galvanometrically positive, its 

 effect on the mucous surface under normal conditions is to 

 induce galvanometric negativity. In the case of Nepenthe, 

 further, we have seen that the natural current of rest is from 

 the non-glandular outer to the glandular inner surface, and 

 that this is liable to reversal, as an excitatory after-effect of 

 preparation. The ingoing current, therefore, observed in the 

 preparation of frog's stomach, is to be regarded, not as the 

 natural current of rest, but as the excitatory after-effect due 

 to isolation. 



With regard, next, to the current of action, Biedermann 

 states that direct electrical excitation, by rapidly alternating 

 shocks, induces a negative variation usually preceded by a 

 positive swing. Since the so-called current of rest is ingoing, 

 a ' negative variation ' of it evidently means an outgoing 

 current that is to say, galvanometric positivity of the 

 mucous coat. Hence the responsive action of the mucous 

 coat, as described by Biedermann, is a transient negativity 

 followed by positivity. 



In dealing with this question of the electrical response 

 of the digestive organ, we must be prepared, as the result of 

 previous experiments on plants, to meet with variations of 

 the excitatory effect, due to the phasic condition of the tissue. 

 And first, for the clear demonstration of the effect of ex- 

 citation on the mucous surface, uncomplicated by changes 

 induced at the second contact, I employed the Rotary 

 Method of Mechanical Stimulation of the given area. The 

 rotating electrodes were applied to the inside of a properly 

 mounted frog's stomach, and experiment commenced some 

 time after the cessation of the multiple response due to 

 preparation. The following record (fig. 210) exhibits the 

 first four of these responses to individual mechanical stimuli, 



