GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 95 



the current, and the longer it is closed. The loss of conduction power is asso- 

 ciated with changes at the place where the current enters and where it leaves 

 the nerve rather than with alterations within the intrapolar region. Engelmann, 

 in his experiments on the smooth muscle-fibres of the ureter, saw a decline of 

 power of conduction at the anode by weak currents, which when the strength 

 of the current was increased appeared also at the kathode ; the conductivity 

 was wholly lost at both poles when the current was very strong. In the case 

 of a striated muscle, such as the sartorius of the frog, the kathode has been 

 found to become impassable after strong currents have flowed through a muscle 

 for a considerable time. The same is true of nerves. 



It is not surprising that a current which can greatly decrease the irritability 

 at the anode, and even inhibit a contraction which may be present when it is 

 applied, should be found to decrease the conductivity as well, but that the con- 

 ductivity should be decreased at the kathode, where the irritability is greatly 

 increased, was not to be expected. Eutherford l found that with weak currents 

 the rate of the conduction power at the kathode was increased rather than 

 diminished, and that it was only when strong currents acted a considerable 

 time that the conduction power lessened at the kathode. Biedermann explains 

 this on the ground that the increased excitability at the kathode leads in the 

 muscle to a condition of latent contraction and therefore to fatigue, and that 

 it is this which lessens the conductivity. The lessened power to conduct con- 

 tinues at the kathode after the removal of the current. There is little doubt 

 that fatigue interferes with the conduction power of muscle, but this explana- 

 tion would hardly apply to nerves which are not known to fatigue at the point 

 of stimulation, i. e. if we limit the term fatigue to changes resulting from 

 physiological activity. Undoubtedly chemical and physical alterations may 

 occur in nerves as a result of the passage of an electric current through them, 

 and it would seem as if the loss of conductivity which they show when sub- 

 jected to strong currents is to be accounted for by such changes. 



The changes produced in the conductivity of nerves by strong currents 

 explain the failure of the closing of the ascending current and opening of the 

 descending current to irritate the muscle (see Pfliiger's law, p. 60). In the 

 former case the anode region of decreased conductivity intervenes between the 

 kathode, where the closing stimulus is developed, and the muscle. In the 

 latter case the irritation developed at the anode, on the opening of the current, 

 is unable to pass the region of decreased conductivity which is formed at the 

 kathode, and which persists after the current is opened. 



Practical Application of Alterations produced by Battery Currents. The 

 alterations produced by strong battery currents in the irritability and conduc- 

 tivity of nerves and muscles may be made use of by the physician. If the 

 effect of only one pole is desired, it may be applied as a small electrode im- 

 mediately over the region to be influenced, while the other pole may be a large 

 electrode placed over some distant part of the body where there are no import- 

 ant organs. The size of the electrodes used determines the density of the 

 1 Journal of Anatomy and Physiologic, 1867, vol. 2, p. 87. 



