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MUSCLE-NERVE PHYSIOLOGY 



15. DuBois-Reymond's Law of Galvanic Stimulation. Connect a single 

 dry cell, a key switch, and a meter-rheocord in circuit. To the zero end 

 of the rheocord attach a lead-off through a pole-changer to one of the 

 non-polarizable boot electrodes of a Harvard moist chamber. Attach 

 the free wire of the lead-off to the other boot electrode. Make a muscle- 

 nerve preparation with a long nerve. Mount in a moist chamber so that 

 the nerve will lie across the two boot electrodes, one quite close to the 

 muscle but not allowed to touch it, and the other as far from the muscle 

 as the length of the nerve will permit. Record on a drum but move the 

 drum by hand. 



The galvanic current (when of moderate intensity) stimulates only at 

 the time of changing intensity, i.e., on making and on breaking the current. 

 Connect the free wire of the lead-off with the rheocord between the 70 

 and zoo cm. points. The exact point will vary, the stronger the battery 

 the nearer to point of attachment to the 70 cm. mark. Note the responses 

 of the muscle, (a) on closing the circuit, (b) during the flow of the current, 

 and (c) at the breaking of the circuit. Make records covering these facts 

 known as DuBois-Reymond's Law of Stimulation. 



1 6. Pfluger's Law of Irritability. Both strength of current and direc- 

 tion of flow of current are factors in the determination of the physiological 

 effects of the galvanic current on irritability. This law is tabulated as 

 follows : 



Determine the direction of flow of galvanic current in your apparatus 

 and demonstrate the several parts of Pfluger's Law as given in the table. 

 Begin with the very weak ascending currents, use one battery with the 

 lead-off attached between 20 and 40 cm. for very weak currents. Reverse 

 the direction of the current by the pole-changer. Use two batteries with 

 lead-off between 50 and 80 cm. for medium currents; and two batteries 

 with lead-off at 90 cm. for very strong current, or four batteries with lead- 

 off at 80 cm. Make records of each contraction and label as to its type 

 and direction. 



17. Electrotonus. The change in irritability at the physiological poles 

 of a nerve through which a galvanic current is passing is called electro- 

 tonus. Mount a fresh muscle nerve preparation in a Harvard moist 



