GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 95 



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 electrolytic changes. 



The changes produced in the conductivity of nerves by Btrong currents 

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

 descending current t<> irritate the muscle (see Pfluger's law, p. 50). In the 



former case the anode regit I" 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 <>J 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 lie 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 

 current leaving or entering the body and consequently the intensity of its 

 action. The application of the anode to a region of increased excitability, by 

 decreasing the irritability, may for the time lessen irritation; on the other 

 hand the kathode may heighten the irritability of a region of decreased 

 excitability. The sending of a strong polarizing current through a motor 

 nerve, by lessening the conductivity, may prevent abnormal motor impulses 

 from reaching muscles, and so stop harmful "cramps;" or the sending of 

 such a current through a sensory nerve may, during the (low of the cur- 

 rent, keep painful impulses from reaching the central nervous system. In 

 applying a strong battery current to lessen irritability or conductivity it 

 must be remembered that the after-effect of such a current is increased 

 irritability. 



(/) Efect of Conduction and Fatigue of Nerves. — Many experiments have 

 been made in the hope of detecting sonic form of chemical change as a result 

 of conduction. The nerve has been stimulated for many hours in succession 

 with an electric current, and then been examined with the utmost care to 

 find whether there had been an accumulation of some waste product, as 

 carbon dioxide, or some other acid body. The gray matter of the spinal 

 cord, which is largely composed of nerve-cells, is found to become acid a- a 

 result of activity, 1 but this cannot be found to be the case with the white 

 matter of the cord, which is chiefly made up of nerve-fibres, nor has an acid 

 reaction been obtained with certainty in nerve-trunks. - 



1 Funke: Archivfur AruUomieund l'liiisi'>l<><)i<\ 1 s ">'.>, S. 835. Ranker Cnitnilblutt fur medicin- 

 ische Wixseiisrlmfl, ISfiS and lNfif). 



2 Heidenliain : Studien aus dem phyaiologuchen Tnalitui ra Bresiau, ix. S. 248 ; Centralblatt fur 



Medicin, 1868, S. 833. Ti.ijersiedt : "Studien iilier iiieclianiselie Nervenreizuni;," Ada Societatia 

 Scientiamm Fennicce, 1880, torn. xi. 



