ELEMENTARY EXPERIMENTAL PHYSIOLOGY 35 



Lesson VII. To be provided for each pair of Students. 



1. Frog killed, one thigh ligatured with exclusion of sciatic nerve, and 

 curare injected. 2. Induction coil, cell, wires, electrodes and keys. 3. Three 

 Daniell cells in series or electric supply from accumulator with resistance or 

 rheocord to vary the strength of the current, keys and wires. 



Secondary 

 Circuit 



FIG. 25. The lower line shows the current as it develops in the primary 

 circuit (shaded part) on closing and on opening ; the upper line shows 

 the instantaneous appearance and disappearance of the current in the 

 secondary circuit and the greater strength of the current induced on 

 opening. In the induced current there is no separation of the make 

 and break. 



(From Noel Paton's Essentials.) 



For the Class. 



1. Microscope with piece of frog's muscle teased in 0'75 per cent. NaCl. 

 2. Microscope with preparation to show the endings of nerve in muscle. 



LESSON VIII 



Stimulation of Nerve and Muscle through the Skin in Man by the 

 Galvanic Current 



Connect wires to the terminals on the switch board G (galvanic 

 current] or lead-off from three Daniell cells in series introducing a 

 rheocord into the circuit (p. 78). Introduce a commutator to change 

 the direction of the current when desired (Figs. 92 and 93). Put 

 some saturated salt solution in a basin and fix the end of one wire to a 

 flat zinc electrode placed in the solution. To the end of the other 

 wire attach a second flat zinc electrode, placing a bit of chamois 

 leather saturated with the salt solution between the electrode and 

 the skin. Dip the fingers of the left hand into the salt solution and 

 apply the second electrode over the back of the thenar muscles. 



First use the cathode. Beginning with a strong current, record 

 the results which follow making and breaking the current. Then, 

 by moving the handle on the switch-board from S to W or by means 

 of the rheocord, reduce the strength of the current, and again 

 record the results which follow making and breaking the current. 



Now reverse the direction of the current by means of the com- 



