THE EFFECTS OF BATTERY CURRENTS ON NERVE-FIBER 471 



ceptibility to conditions which influence metabolism in other forms of proto- 

 plasm. Perhaps the nerve fiber is capable of repairing its wastes as rapidly 

 as they occur. 



The Effects of Battery Currents on Nerve Fiber. Galvanic currents 

 influence nerves in ways that call for special discussion. A constant cur- 

 rent, say from a Daniell battery, can be introduced into the nerve of a 

 muscle-nerve preparation by means of a pair of non-polarizable electrodes, 

 figure 3 2 3, and a convenient key arranged for turning the current on or off the 

 nerve. It will be found that with a current of moderate strength there will be a 

 contraction of the muscle, both at the closing and the opening of the key (called 

 respectively making and breaking contractions), but that during the interval 

 between these two events the muscle remains flaccid, provided the battery cur- 

 rent continues of constant intensity. If the current be a very weak or a very 

 strong one, the effect is not quite the same; one or the other of the contractions 

 may be absent. Which of these contractions is absent depends upon another 

 circumstance, viz., the direction of the current. The direction of the current 

 may be ascending or descending: If ascending, the anode or positive pole is 

 nearer the muscle than the cathode or negative pole, and the current to return 

 to the battery has to pass up the nerve; if descending, the position of the elec- 

 trodes is reversed. It will be necessary before considering this question 

 further to return to the apparent want of effect of the constant current during 

 the interval between the make and the break contraction. To all appear- 

 ances no change is produced, but in reality a very important alteration of 

 the irritability and conductivity is brought about in the nerve by the passage 

 of this constant or polarizing current. 



A second way of showing the effect of the polarizing current is by stimu- 

 lating the nerve by a pair of electrodes from an induction coil, while the polar- 

 izing current from the battery is flowing through the nerve. If the strength of 

 stimulus required in order that a minimum contraction be obtained by the 

 induction shock before the polarizing current is applied, and the secondary 

 coil be removed slightly further from the primary, the induction current 

 cannot now produce a contraction. If now the polarizing current be sent in a 

 descending direction, that is to say, with the cathode nearest the muscle, and 

 the induction current which was before insufficient be applied between the 

 cathode and the muscle, it will now prove sufficient to cause a contraction. 

 This indicates that with a descending current the irritability of the nerve is 

 increased at the cathode. If instead of applying the induction electrodes 

 below the polarizing electrodes, they are applied above them, the irritability of 

 the nerve is found to be decreased. If the polarizing current is reversed, i.e., 

 made ascending, then the condition of irritability of the nerve is reversed. 

 Both methods show that the polarization consists in an increase in irritability 

 at the cathode, called catelectrotonus, and a decrease at the anode called 

 anelectrotonus. The total change is called by the term electrotonus. As there 



