ON THE MAMMALIAN NERVOUS SYSTEM. 467 



of any one particular column, pass to reach the nerve roots. It cannot be assumed 

 that the result of the excitation of any particular column is to evoke nerve impulses 

 which, in their passage to the issuing nerve roots, are limited to fibres in this 

 particular column, or that any particular excitation, however strictly localised, may 

 not excite by commissure! fibres a neighbouring column. Indeed, as far as the cord 

 itself is concerned, the evidence afforded by the experiments (Chapter VIII.) shows 

 there is no absolute limitation of descending impulses to one column. 



It is, therefore, a matter of great importance in connection with the present 

 investigation to ascertain to what extent in the foregoing experiments the path of 

 such impulses as issue by the nerve roots is limited in the cord to the particular 

 column stimulated. We endeavoured to obtain information as to this in the 

 following manner : we first made experiments with the mixed nerve precisely 

 similar to those already described (Section 3), that is, we connected the nerve 

 with the galvanometer circuit, and excited the cut ends of the various columns 

 of the cord, as displayed in a transverse section. We then made a section of one 

 column between the seat of excitation and the lumbar roots of the sciatic nerve, and 

 repeated the first experiment under these conditions. We were thus enabled to 

 ascertain how far the nerve effect due to the excitation of any particular column was 

 reduced when the fibres of that column were all cut through. Any remaining effect 

 might be due to 



(a.) The presence of fibres which passed from the stimulated into other columns; 



(?&amp;gt;.) The presence of fibres connected with the corpuscular portion of the cord, and 

 the awakening of the same by their means, the nervous impulses thus reflexly 

 discharged proceeding either along fibres in other columns or along fibres in the same 

 column below the interruption. 



To what extent these various factors come into play will be made evident by a 

 careful analysis of all the results. These are best grouped in accordance with the 

 particular part of the cord which was the seat of the intervening section. 



A. Influence on the Effect in the Nerve of Hemisection of the Cord. 



The first group of results show that an intervening hemisection of the cord 

 completely abolishes the nerve effect produced by excitation of the columns on the 

 side of section, as well as that evoked by excitation of the posterior column of the 

 opposite side. 



Thus the spinal cord was exposed and divided in a Cat (329) at the level of the 

 9th dorsal vertebra ; both sciatic nerves were now prepared for galvanometric observa 

 tion, and the electrical effects obtained by exciting the cut section of the various 

 columns at the 9th dorsal vertebra observed, the results being given as under. 



3 o 2 



