GRAPHIC REGISTRATION OF MUSCULAR CONTRACTION 



63 



space between them. A similar induction is developed when the primary current 

 is broken. During the interim, however, there is no induction in spite of the fact 

 that the current in the primary coil continues without interruption. 



If the direction of the induced current is now determined by means of a gal- 

 vanometer, it is found that the making induction shock is opposed to the primary 

 current, while the breaking induction shock possesses the same direction as the 

 primary current. It should also be emphasized that the make induction develops 

 more slowly than the break induction. This difference is due to the fact that the 



Fig. 32. — The Inductorium (DuBois-Reymond). 

 A, primary coil; B, secondary coil; P', binding posts for wires from battery; j/' 

 binding posts for wires leading to stimulating electrodes. {Howell.) 



entering primary current must first of all overcome the self-induction of the primary 

 coil before it can produce its characteristic effect in the secondary coil. While it 

 passes from segment to segment of the primary wire, an induced current is momen- 

 tarily set up in the more distant stretch of wire which pursues a direction opposite 

 to it and tends therefore to lessen its strength. Until this resistance has been over- 

 come, it cannot possibly exert its full energy upon the secondary circuit. On ibhe 

 break, however, this hindrance is not present, so that the induction in the secondary 

 coil can reach its maximum with much greater rapidity. For this reason, the break 



Fig. 33. — The Inductorium. 

 I, primary circuit and coil; 11, secondary coil and circuit; K, key; J, automatic 

 interrupter; N, nerve. 



shock always stimulates living substance more intensely than the make shock. 

 The constant current, on the other hand, stimulates more on the make, i.e., at 

 the time when it first enters the living substance with its initial amplitude. 



The strength of the induction shocks depends first of all upon the strength of 

 the primary current and therefore also upon the strength of the battery. In the 

 second place, it is proportional to the distance between the two coils, i.e., it be- 

 comes the weaker, the farther the secondary coil is removed from the primary. 

 Thus, we generally estimate the strength of an induction shock by determining the 



