TWO SUCCESSIVE SHOCKS. 



185 



(a.) Charge four Daniell cells, and connect two with one 

 induction machine and two with another, introducing one 

 trigger-key in the primary circuit of one induction machine, 

 and the other trigger-key in the primary circuit of the other 

 one. If the pendulum myograph be used, let the trigger- 

 keys be about 5-8 centimetres apart. Connect the two 

 secondary coils by a wire stretching between the two adjacent 

 terminals. The other two terminals are connected with 

 a short-circuiting du Bois key, from which the electrodes 

 proceed. 



(b.) Arrange a muscle or nerve-muscle preparation either 

 in a moist chamber or on a crank myograph; place the 

 electrodes under the nerve or stimulate the muscle directly. 



(c.) Take a tracing in the ordinary way, after unshort- 

 circuiting the secondary coils, and seeing that both primary 

 circuits are closed. On discharging the instrument, first the 

 one key and then the other is opened. It is necessary to 

 ascertain beforehand that both break shocks are nearly of 

 the same intensity. Take a series of tracings, gradually 

 diminishing the distance between the two trigger-keys. In 

 each case record the movement of stimulation with each 

 trigger-key. 



Fig. 77 Wild's apparatus for studying the action of poisons on muscle. 

 D, Drum ; P, platform j S, stand ; al, after-load ; L, lever ; B, bottle 

 with muscle ; K', key. 



2. Wild's Apparatus consists of a glass cylinder made by 

 inverting the neck end of a two-ounce phial. The neck is fitted 



