GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 



93 



tion is maintained. To this current the term decremential is given. 

 When a muscle is excited to action by the nerve impulse which en- 

 ters 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. 



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

 during a single contraction was demonstrated by Hermann in the mus- 

 cles of the forearm. The arrangement of the experiment was, briefly, 

 as follows : The forearm was surrounded by two twine electrodes sat- 

 urated with zinc solution, one being placed at the physiologic middle 

 the nervous equator the other at the wrist. Both electrodes were 

 then connected with the galvanometer. When the brachial plexus was 

 stimulated in the axillary space, the deflections of the galvanometer 



FIG 37. THE CONDITION LEADING TO THE DEVELOPMENT OF THE SECOND ACTION 



CURRENT. 



needle, when analyzed with the repeating rheotome, indicated phasic 

 currents with a single contraction. In the first phase atterminal 

 the wrist became positive and the current passed in the muscle toward 

 its termination; and in the second abterminal it became negative 

 and the current now passed in the reverse direction. The action 

 currents which are observed in the frog's muscle were thus shown 

 to be present in the living human muscle, with this difference, how- 

 ever: that the second phase, abterminal, instead of being weaker 

 in man, is equally strong with the atterminal. This experiment also 

 revealed the fact that the rapidity of propagation of the excitation 

 wave was much greater in man, amounting to about twelve meters 

 per second. Hermann therefore denies the preexistence of electric 

 currents and regards them as due to localized temporary disintegra- 



