LABORATORY MANUAL OF PHYSIOLOGY. 



ligature about the nerve as high up as possible. Cut the nerve 

 above the ligature. Place the cut nerve on shielded electrodes, 

 connected with the secondary coil of an inductorium. Place the 

 primary of the inductorium in circuit with a strong constant cur- 

 rent interrupted by the tuning-fork interrupter, vibrating one 

 hundred times per second. Place a short-circuiting key in the 

 secondary circuit. Place the small bell of a stethoscope over the 

 muscle. Open the short-circuiting key. The muscle will be 

 thrown into tetanus and the sound of the vibrating tuning-fork 

 will be heard with the stethoscope. That this reproduction of the 

 tuning-fork tone is really due to the vibration of the muscle fibres 

 to each individual stimulus from the inductorium is shown by 

 the next experiment. 



10. Action Currents. Detection of, with the Telephone. 

 With the same preparation as in the previous experiment, insert 

 needle electrodes into the body and tendinous portion of the gas- 

 trocnemius muscle. Connect these with a telephone receiver and 

 again stimulate the sciatic with one hundred shocks per second. 

 You will now hear the sound of the tuning-fork reproduced in 

 the telephone. This is due to the development of action currents 

 in the muscle corresponding, in frequency, to the number of im- 

 pulses coming to the muscle. 



This sound is known as the artificial muscle tone, to distinguish 

 it from the muscle sound which occurs when the muscle is con- 

 tracted under the influence of volition and which is called the nat- 

 ural muscle tone. 



This may be heard by placing the stethoscope on the biceps 

 muscle and strongly flexing the forearm on the arm. 



XXI. IRRITABILITY AND CONDUCTIVITY OF NERVE AND MUSCLE 

 DURING AND AFTER THE PASSAGE OF A CONSTANT CUR- 

 RENT. ELECTROTONUS. 



During the passage of a constant current through a nerve, the 

 irritability and conductivity are increased at the kathode, where 

 the current leaves the nerve, and diminished at the anode, where 



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