194 STUDIES IN ELECTRO-PHYSIOLOGY: 



may mean. Let us take two nerves, a motor and a 

 sensory, and see what would happen if they were both 

 severed in life. 



In the case of the motor nerve the battery is in the 

 brain with one pole to earth (air), while the nerve the 

 wire, as it were is also to earth through tissue and skin. 

 The effect of the cut is to remove 

 the conductor, qua conductor, below 

 the node immediately above the cut 

 and to an imaginary line a, b (Fig. 104). 

 The whole of the apparatus above 

 the line a, b would be structurally and 

 electrically intact, and the line a, b, 

 if of high resistance, would be equiva- 

 lent, in hydrostatic parlance, to a 

 ligature applied to an artery or a vein. 

 Precedent to repair or regeneration 

 of the lower portion, no muscle below 

 the cut could receive an impulse. 

 If, however, the axis-cylinder were 

 continuous through the node there would be a path of 

 low resistance at the node an escape of current into wet 

 tissue and the muscles above the cut could only receive 

 stimuli at a greatly lowered pressure. 



In a sensory path the need of a synaptic node is even 

 greater, for the sensory nerves are closed circuits, and they 

 have many ramifications in motor as well as other sensory 

 paths over which they transmit impulses in various 

 directions. To take a simple sensory path, however, from, 

 say, skin to post -spinal ganglion. 



Here we have a charged wire, a unipolar guard-cell or 

 cells to maintain normal potential in that wire, and a 

 receiving instrument in the cord. If the nerve were severed 

 no impulse could be conveyed, but, given the line of 

 resistance a, b, the upper part of the nerve from the first 



