512 SCIENCE PROGRESS. 



Two pupils of Hermann, Bach and Oehler, continued 

 the work, and made the important observation that the 

 direction of the action current could be varied at will by- 

 certain methods of treatment, viz., heating to 50 c, pencilling 

 the skin with saturated mercuric or sodic chloride solutions, 

 and by repeated excitation. By such procedure, an action 

 current previously outgoing in direction could be made in- 

 going, though naturally by such treatment a fall in the 

 electromotive force of the "current of rest" was to be 

 expected, and, indeed, was observed. 



Bach and Oehler also found that atropine abolished the 

 excitatory variation, making it all the more probable that 

 such variation is of glandular origin. 



By the treatment with mercuric chloride, it was found 

 that while the "current of rest" could often be completely 

 annihilated, a "current of action" could still be elicited, 

 and this fact, together with his observation, that the skin of 

 the fish (which he considered "non-glandular") gave an 

 ingoing "current of rest," led Hermann in a second paper 

 to formulate a distinct theory of the electromotive action of 

 the frog's skin. 



The electromotive force of the "current of rest" (since 

 he found such a current in the so-called " non-glandular " fish 

 skin) Hermann considered as epidermic in origin, and on 

 the Alteration theory to be produced by the keratinisation 

 of the surface of the epidermis acting as a demarcation 

 surface in protoplasmic continuity. No component of the 

 current of the spheroidal skin glands with closed ducts is 

 considered as derivable at the surface touched by the elec- 

 trodes, so long as the glands are in the resting state. 



On excitation, however, the contraction of the gland 

 puts the interior into direct communication with the surface 

 by the extruded thread of slime. Should the electromotive 

 force of the gland cells be less than that of the epidermic 

 cells at the moment that the "lead off" is established, a 

 " negative variation " of the skin current must occur. When, 

 however, the gland cells become active (and in the case just 

 mentioned one is supposed to be within the latency of the 

 secreting cells, though, of course, not within that of the 



