150 PHYSIOLOGY OF MUSCLES AND NERVES. 



with great speed,' the nerve is excited and the muscle 

 pulsates. When, therefore, the current being closed 

 or opened bj means of the key, the nerve is excited, 

 this is due to the fact that the strength of the current 

 increases with great rapidity from zero to its full 

 strength, or sinks from the latter to zero. 



The facts thus observed explain why inductive 

 shocks, which are of but very short duration, and in 

 which closing and opening follow each other in such 

 rapid succession, are so especially capable of exciting 

 the nerve. All inductive shocks are not, however, 

 equally adapted for this purpose. When, making use 

 of the inductive apparatus already described, the current 

 in the primary coil is closed and then interrupted, the 

 result is the creation of two currents differing in their 

 direction in the secondary coil, these being the closing 

 inductive current and the opening inductive current. 

 If these are made to pass through a nerve, the exciting 

 influence of the latter is always much greater than that 

 of the former. This can be very plainly shown by 

 placing the secondary coil at a distance from the pri- 

 mary. By this means, a distance may always be found 

 at which the opening inductive current is active, while 

 the closing inductive current as yet exercises no in- 

 fluence ; if the coils are then brought nearer to each 

 other, the latter also becomes active. If, however, 

 when the coils of the inductive apparatus are in any 

 position, the secondary coil is connected with a multi- 

 plier, then the deflections of the magnetic needle are 

 always of equal strength in the case of both inductive 

 currents. The nerve, therefore, exhibits a difference 

 which the multiplier is incapable of indicating. It has, 

 however, been shown that the two inductive currents 



