ON THE MAMMALIAN NERVOUS SYSTEM. 



503 



CAT (268). Influence of Section of Anterior Roots on the Excitatory Effect in the 

 Nerve, when one Posterior Root is excited in continuity. 



On summing up these experiments it is evident that the division of the anterior 

 roots does raise the value of the effect in the sciatic nerve evoked by excitation of a 

 posterior root in continuity. In the last three experiments thab rise is not so greatly 

 marked as to be more than the supplementary discharge of the spinal centres might 

 account for, but this, of course, does not explain the high readings in the first case. 



SECTION 5. THE SPKEAD OF REFLEX DISCHARGES UP AND DOWN THE COED 



(INTERNUNCIAL FlBREs). 



We have frequently spoken of the existence of internuncial fibres connecting the 

 various centres. It must, however, be confessed that the evidence of their existence is 

 founded almost entirely upon our knowledge of the laws of reflex spread as stated by 

 PFLUGER. (See Section 1, p. 484.) 



We endeavoured to ascertain what light the present galvanometric method would 

 throw upon this spread, and thus upon the localisation and characteristics of these 

 paths. To elucidate this we made a series of experiments in which the cord was 

 excited and the electrical changes noted at the same time that the muscular 

 movements were either recorded or carefully observed. 



(1.) Ascending Discharges (Reflex). 



In the case of reflex discharges it is possible, after division of the cord, to observe 

 the electrical changes in the upper end of the lower fragment of cord, and at the same 

 time to note the contractions of a muscle of the lower (hind) limb. 



