332 PRESENT STATE OF ORGANIC ELECTRICITY. 



of the longitudinal and transverse sections cannot be detected 

 before the nervous cord has been cut across. If a transverse 

 section is in contact with one electrode, and the outer surface 

 of the nerve with the other, the current passes through the 

 galvanometer wire from the latter to the former. The current 

 has the same relative direction whether the transverse section 

 belong to the peripheral or central extremity of the nerve ; 

 and, consequently, when a segment of nerve is doubled in the 

 middle, the current passes from the loop to both sections. 

 The currents derived from the natural longitudinal section 

 that is, the outer surface of the segment of a nerve are simi- 

 lar to those derived from the outer aspect of a muscle ; and 

 there is reason for believing that if the small size of the 

 transverse section did not present an obstacle, it also would 

 be found to be in the same condition of electric tension as a 

 corresponding surface in a muscle. 



It is a remarkable and important fact that no difference 

 exists in the laws of the electric current in the two classes of 

 cerebro-spinal nerves. The motor and sensory nerves, the 

 dorsal and ventral roots of the spinal nerves, and the nerves 

 of special sense, all present the same electric conditions. It 

 is also remarkable that the spinal marrow and brain afford 

 the same results as the nervous cords. The former has its 

 natural and artificial longitudinal surfaces in a positive electric 

 condition, and its transverse in a negative. In a brain the 

 entire surface covered by the pia mater, whatever complication 

 of form or direction it may assume, being morphologically a 

 longitudinal surface, is electrically positive in relation to 

 artificial sections of the organ. 



Du Bois Eeymond has discovered a very remarkable con- 

 dition of a nerve produced by the passage of a continuous 

 electric current through a portion of it. If a continuous 

 current be passed along a portion of a separated segment of 

 nerve, it alters the ordinary electromotor condition of the 



