ON THK MAMMALIAN NKIIVOUS 8YHTKM. 



Tho root, therefore, in thiH respect behaves, as far UH these two experiments enable 

 us to judge, like the nervo. 



(c.) Changes following Excitation. In consequence of oithor direct excitation of 

 the root or its indirect excitation through the cord, the amount of tho difference is 

 decreased, an after-effect following the pasting away of the true excitatory change 

 similar in character to that seen in the nerve. 



Tho rising and falling in the amount of the difference when the anesthesia of the 

 animal is not sufficiently profound is rather more marked in tho case of tho posterior 

 root than in that of tho mixed nerve. 



C. ANTKUIOK HOOT. 



With regard to the anterior roots, wo have only performed one experiment. There 

 are considerable difficulties in the way of connecting tho anterior root satisfactorily 

 with the electrodes, so as to exclude all possibility of obtaining results which are 

 derived from electrical changes in the cord. These difficulties are mainly the shortness 

 of the root and the characters of its anatomical relations with tho cord, it heing 

 difficult to obtain a suflicient length. Moreover, our purpose being rather to obtain 

 the evidence of excitatory than of resting electrical changes, tho shortness of tho root, 

 when combined with tho movements of tho animal, caused serious errors in observa 

 tion, due to the displacement of tho electrodes and their being thus brought near to or 

 in contact with surrounding structures. In the single case in which the Cth left 

 lumbar anterior root was divided and its central end connected with tho galvanometer 

 electrodes, the difference (Cat) was found to l&amp;gt;e only OO-if) Danicll, whereas the Oth 

 lumbar posterior root of the same side, when examined, showed a difference of 

 012 Daniel I. 



1). SPINAL CORD. 



The fact that the cord exhibits, like tho nerve, both a persistent difference between 

 its longitudinal surface and its cross section and a true excitatory effect, was dis 

 covered by DU BoiS-RKYMOND, and has been since confirmed by other observers, notably 

 SKTCCHKNOW. The general features of tho same were described by us in our preliminary 

 communication made to the Iloyal Society, but a systematic analysis of a number of 

 observations has never, that we are aware, been made, nor has tho amount of tho 

 persistent difference been determined. In the course of our investigations we have 

 noted the amount and characteristics of the resting difference in the spinal cords of 

 sixty-three Cats and fourteen Monkeys, and tho results arranged in groups are given 

 in Appendix H. 



Tho most striking characteristics of the resting difference in the cord and the 

 contrast between this difference and that of the nerve may be roughly seen after tho 

 death of the animal (Cat, Rabbit, &c.) by rapidly exposing a length of cord and of 



