ON THE MAMMALIAN NERVOUS SYSTEM. 315 



TABLE of Results after Previous Operations. 



012 after section of posterior roots. 



017 ,, hemisection. 



018 



'022 section of both posterior columns. 



025 :J one 



Total -094 



Average.. '019 Darnell approx. 



2. Alterations in Resting Difference. 



The electrical difference between the surface and cross section of the spinal cord 

 alters during observation in the manner already described in treating of the sciatic 

 nerve and root, but the alterations are much more marked. 



(a.) Physical Changes. The effect of drying is the same as in the case of the 

 nerve, the amount of the resting difference continuing to rise steadily after exposure 

 and isolation of the cord unless great care is taken to keep it moist. It is difficult to 

 ascertain with precision to what degree this physical change is capable of causing a 

 rise in the difference, this rise being about '0001 Daniell in five minutes ; but that it 

 is by no means the sole agent is shown by the fact that even when the exposed 

 cord is kept moist by steaming sponges with as much care as possible, the rise con- 

 tinues, though more slowly than when no such precautions are used, as also by the 

 facts to be referred to in the succeeding paragraphs. It is, however, important to 

 keep in view in the consideration of alterations supposed to be due to strictly physio- 

 logical agencies the influence of these purely physical ones. 



(6.) Physiological Changes, not obviously Excitatory. The alterations due to 

 physiological changes are associated with both a rise and a fall in the amount of 

 difference, and are much more marked in the case of the cord than in that of the 

 nerve or the root. The amount of the rise is demonstrated in the following obser- 

 vations, in all of which the cord having been exposed, ligatured, arid divided, was 

 suspended by its unattached end and connected with the electrodes in the manner 

 described before. 



It was then observed that in every case the resting difference between the surface 

 and cross section increased rapidly for the first five minutes or more after the isolation 

 had been made, provided that the cord was still in connection by its deep attachment 

 with a part which, being in situ, was in its normal physiological state of nutrition. 

 The amount of this initial rise varies considerably in different cords, but the average 

 in 19 cases amounted to '0016 Daniell, the highest rise being '003 and the lowest 

 '001. The duration of this comparatively rapid rise is, on the average, about five 



2 s 2 



