3l6 COMPARATIVE ELECTRO-PHYSIOLOGY 



out by Dr. Waller, 1 on the isolated paw of a cat. The 

 current of rest was found by him to flow from the surface 

 of the pad to the section. From this he was led to the 

 conclusion that this current could not have been due to 

 injury, since in that case it would have flowed from the 

 sectioned to the uninjured surface, and not in the opposite 

 direction, as was found to be the case. 



This misconception arises from a failure to realise that 

 the so-called ' current of injury ' is, in fact, an after-effect of 

 excitation. In the case under consideration, the section, 

 acting as an intense stimulus, simply induces greater excita- 

 tory reaction of the more excitable, which in this case 

 happens, as we should have expected, to be the glandular 

 surface. The injury-current here, then, is necessarily from 

 the more excited glandular to the less excited non-glandular. 



A precisely similar result was obtained in the case of 

 anisotropic plant-organs, where excitation caused by injury 

 of the less excitable side, becoming internally diffused, 

 induced greater galvanometric negativity of the more ex- 

 citable distal point (p. 162). For a typical experiment on 

 a glandular preparation, showing the principal effects, and 

 the complications that may arise owing to injury, we may 

 take the detached foot of the pond-snail, the lower surface of 

 which, as is well known, secretes a slimy fluid. On allowing 

 for the necessary period of rest, and then making electrical 

 connections, we observe a current of rest, so-called, which 

 flows from the glandular to the sectioned end. This is not 

 to be mistaken for the true natural current of rest, being in 

 fact the after-effect of a greater galvanometric negativity at 

 the more excited glandular surface, consequent on section. 

 An independent experiment, in support of this induction, 

 will be described presently. On now simultaneously ex- 

 citing the two surfaces, by equi-alternating shocks, the 

 responsive current is found to flow from the gland inwards, 

 the more excitable gland becoming thus galvanometrically 

 negative. The responsive current is in this case in the same 

 1 Waller, Signs of Life, p. 101. 



