340 ELECTRO- PHYSIOLOGY CHAP. 



affords a simple explanation of the vigorous, normal current of 

 the apparently uninjured gastrocnemius, as also of the irregular 

 effects which may be produced on leading off from tendon and 

 natural longitudinal section of the different thigh muscles. But 

 it is evident that, under the given conditions, the state of no 

 current must be regarded as normal. If it could be proved 

 that all muscles in the perfectly uninjured state are invariably, 

 and under all conditions, currentless, the hypothesis of a special 

 layer working in a contrary direction at the natural section would 

 obviously be superfluous. The entire controversy as to the pre- 

 existence of the muscle current turns, therefore, as Hermann said, 

 upon whether it can be demonstrated before the animal is skinned, 

 on the muscle in situ, with normal circulation. This might seem 

 comparatively easy on the frog, since its moist, thin skin lies 

 loosely on the muscles, and forms a relatively effective sheath. 

 And it is in fact the most favourable object for the experiment. 

 Du Bois-Beyrnond devoted much time and trouble to the in- 

 vestigation of the muscle current in the living, uninjured frog 

 with intact skin, and concluded, finally, that normal differences 

 of potential did exist in the sense indicated. Nevertheless, this 

 also appeared later to lie an interpretation against which serious 

 objections can be urged. In leading off from frogs, and frogs' 

 limbs, with intact skin, du Bois-Keymond again employed 

 trough electrodes, filled with concentrated Nad, and covered 

 with an " albumen membrane." It was soon found that the 

 contact first applied was always positive to the second contact, so 

 that after some time a current of low E.M.F. appeared, in the 

 direction of the longitudinal current in a skinned frog. The first 

 effect depends, as du Bois found, upon an electromotive force in 

 the skin of the frog itself. It is here sufficient to state that the 

 E.M.F. of the skin is vertical to its surface, current being 

 directed from without inwards (of course reversed in the galvano- 

 meter circuit). Now since these strong natural effects are easily 

 disturbed by moistening the outer surface of the skin with 

 corrosive fluids, there must always be a current in the above 

 sense when the skin is brought into unequal contact with the 

 leading-off electrodes, since these are not perfectly indifferent, i.e. 

 the less effective, or ineffective, point becomes positive to the 

 other. 



It might be expected that the normal current from the 



