MUSCLE-STIMULI. 



451 



The current of a battery may be used to stimulate a muscle, but 

 an induced current is more commonly employed on account of the 

 greater efficacy of its action. The instrument in ordinary use in 

 physiological laboratories is Du Bois-Reymond's inductorium, in 

 which the strength of the stimulus can be reduced by removal 



FIG. 183. 



I 



Du Bois-Reymond's Inductormm with Magnetic Interrupter. c. Primary 

 coil through which the primary, inducing, current passes, on its way through 

 the electro-magnet (6). t. Secondary coil, which can be moved nearer to 

 or further from the primary coil (c), thereby allowing a stronger or weaker 

 current to be induced in it. This induced current is the stimulating one. 

 6. Electro-magnet, which, on receiving the current, breaks the contact in 

 the circuit of the primary coil by pulling doAvn the iron hammer (h), and 

 separating the spring from the screw of e. When it brings the spring in 

 contact with the point of the pillar (a), it also demagnetizes itself by " short- 

 circuiting " the battery. When tetanus is to be produced, the wires from 

 the battery are to be connected with g and d. When a single contraction 

 is required, the magnetic interrupter is cut out by shifting the wire from a 

 to the binding screw to the right of/. 



of the secondary coil, and which is supplied with a magnetic in- 

 terrupter, by means of which repeated stimuli may be given. 

 (See Fig. 183.) 



