64 



PHYSIOLOGY OF MUSCLE AND NERVE 



distance of the coils in centimeters in conjunction with the strength of the cells in 

 volts. 1 It need scarcely be mentioned that the induction may also be diminished 

 by placing the secondary coil at an oblique angle to the primary. When at right 

 angles to one another, the secondary current fails to develop. 



The primary current may be made and broken at different intervals, an induc- 

 tion resulting each time. When interrupted very rapidly, the inductions in the 

 secondary circuit follow one another in such quick succession that they are fre- 

 quently designated as a faradic or tetanic current. In order to avoid in the latter 

 case the opening and closing of the key with the hand, an interrupter has been 

 provided which automatically makes and breaks the primary current. The one 

 devised by Neef consists of a vibrating steel rod ( V) and a magnet (-B) . The current 



FIG. 34. THE AUTOMATIC INTERRUPTER OF THE INDUCTORIUM (NEEF'S). 

 A, entrance of current from battery into post B and vibrator V as far as D. In 

 accordance with the position of the vibrating plate, the current now flows either back to 

 the battery C through post F or into the primary coil PC through D. In the latter 

 case, the current first traversea magnet E before it can reach the battery by way of 

 post F. 



from the battery (A) is led into the pillar B as far as the platinum contact (D) 

 upon the vibrator. If the latter is in contact with the end of the wire of the pri- 

 mary coil (PC) at D, the current traverses this spiral and returns to pillar F and 

 the battery (C) by way of a double spiral (E) . But as the current passes through 

 spirals E, their iron cores are magnetized and attract the iron plate H of the 

 vibrator, thus breaking the contact of the vibrator at D. The current then 

 flows directly into F and back to the battery (C) by way of contact K. When 

 the primary current is broken in this way, the spirals (E) are again demagnetized. 

 The iron plate (H) being released, the vibrating rod moves upward and again makes 

 contact at D. At the very moment when the primary current is thus made and 

 broken, an induced current is developed in the secondary coil which, however, is 

 not shown in figure 34. 



1 Martin, Am. Jour, of Physiol., xxviii, 1911, 49. 



