LABORATORY MANUAL OF PHYSIOLOGY. 



With a strong current, tetanus sometimes occurs both at the 

 make and the break. 



1. Experiment. Set up 8 or 10 dry cells in series. Place a 

 commutator and simple key in circuit with the brass electrodes to 

 be used for the stimulation of the human nerve. Place the anode 

 electrode on the back of the neck and the kathode over the ulnar 

 nerve at the elbow. 



(a) Make and break the circuit with the simple key. If there 

 is no accompanying muscular contraction, add more cells to the 

 circuit until a contraction is obtained. Record results and com- 

 pare with the table given above. 



(b) Change the direction of the current by means of the com- 

 mutator key so as to make the electrode, over the nerve, the anode. 



Again make and break the circuit, starting with weak currents 

 and increasing the strength of current as before. Keep a careful 

 record of the various strengths of current and the appearance of 

 the different contraction responses. 



2. Reaction of Degeneration. In a muscle whose nerve has 

 been cut off from its controlling cell, after a time certain definite 

 changes in irritability to the constant and induced currents occur. 

 There is a gradual diminution in excitability to the induced cur- 

 rent and at first an increased excitability to the constant current. 

 Later, this diminishes also. The muscle contraction may also be- 

 come greatly prolonged and a condition called galvanotonus (tonic 

 contraction) may be easily produced. The normal contraction 

 formula is departed from, the most characteristic change being a 

 reversal of the usual appearance of KCC and ACC. Normally, 



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