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TEXT-BOOK OF PHYSIOLOGY 



observed, which, however, endures so long as the tetanic contraction is 

 maintained. To this current the term decremential is given. When a 

 muscle is excited to action by the nerve impulse which enters at its center, 

 two contraction waves are developed, one in each half of the muscle, and 

 hence there are two sets of diphasic action currents. 



FIG. 37. THE CONDITION LEADING TO THE DEVELOPMENT or THE FIRST ACTION 



CURRENT. 



The presence of action currents in the muscle of the living body during a 

 single contraction was demonstrated by Hermann in the muscles of the 

 forearm. The arrangement of the experiment was, briefly, as follows: 

 The forearm was surrounded by two twine electrodes saturated with zinc 



FIG. 38. THE CONDITION LEADING TO THE DEVELOPMENT OF THE SECOND ACTION 



CURRENT. 



solution, one being placed at the physiologic middle the nervous equator- 

 the other at the wrist. Both electrodes were then connected with the galvan- 

 ometer. When the brachial plexus was stimulated in the axillary space, the 

 deflections of the galvanometer needle, when analyzed with the repeating 

 rheotome, indicated phasic currents with a single contraction. In the first 



