142 



THE PHYSIOLOGY OF NERVE 



very largely to the low intensity of the metabolism of this tissue as 

 well as to its remarkable affinity for oxygen. Nerve-tissue is capable 

 of assimilating this gas in the briefest possible time from almost any 

 source. In this regard nerve differs materially from the cell-bodies 

 of the neurons, because the latter display a very intense metabolism 

 and may therefore be more easily fatigued. 



CHAPTER XIII 



THE REACTION OF NORMAL AND ABNORMAL NERVE AND 



MUSCLE TO THE CONSTANT AND INTERRUPTED 



ELECTRICAL CURRENTS 



Electrotonus. — The subsequent discussion should prove of par- 

 ticular value, because the facts now to be dealt with are absolutely 

 essential for a thorough understanding of the behavior of human nerve 

 and muscle when affected by degenerative changes. If we confine our- 

 selves for the present to the constant or galvanic current, it is to be 

 noted that the nerve must first be connected with the battery by means 

 of two non-polarizable electrodes which are placed at a moderate dis- 



FiG. 84. 



-Schema^ to Show the Arrangement Used for the Stimulation With 

 THE Descending or Ascending Current. 

 D, descending; A, ascending. 



tance from one another. The electrode joined with the positive pole 

 of the generator then serves as the point of entrance of the current 

 into the nerve, and the one united with the negative pole, as its point 

 of exit. The former constitutes the anode (+) and the latter the 

 cathode ( — ). Provision must also be made to be able to change the 

 potential of these electrodes at will. This end is attained by means 

 of a pole changer. In this way, the anode may be placed either near 

 to or far away from the central end of the nerve (Fig. 84). If the 

 former, the current must sweep over the nerve in a direction from cen- 

 ter to periphery. It is then known as a descending current. If the 



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