1 66 



PRACTICAL PHYSIOLOGY. 



[XXVII. 



14. Thomson's Reverser (fig. 93) may be used to reverse the direction of a 

 constant current. The wires from the battery are connected to the two lower, 

 and those from the electrodes to the upper binding screws. The binding 

 screws are four in number, and placed behind the circular disc seen in the 

 figure. When the handle is horizontal the current is shut off from the 

 electrodes, while the direction of the current is reversed by raising or 

 lowering the handle. This instrument is used solely for reversing the 

 direction of a current. 



LESSON XXVII. 



INDUCTION MACHINE ELECTRODES. 



1. Induced or Faradic Electricity is most frequently employed 

 for physiological purposes. Induction shocks are of short dura- 

 tion, while they are physiologically very active, and they may be 

 employed as single shocks, or a succession of shocks may be applied. 

 Indeed, the fact that the application of successive induction shocks 



FlG. 94 Induction Apparatus of Du Bois Raymond. R'. Primary, R". Secondary spiral ; 

 B. Board on which R" moves ; /. Scale ; + - . Wires from battery ; P, P". Pillars ; 

 H. Neef's hammer; B'. Electro-magnet ; &. Binding screw touching the steel spring 

 (0; S", and S"'. Binding screws to which are attached wires when Neef's hammer 

 is not required. 



but slightly impairs the physiological activity of the tissues, and 

 that the intensity of these shocks can be accurately graduated, make 

 induced electricity so valuable as a stimulus in physiological 

 experiments. 



2. Induction Apparatus of Du Bois-Keymond. In fig. 94 the 

 primary coil (R') consists of about 150 coils of thick insulated 

 copper wire, the wire being thick to offer slight resistance to the 



