462 MESSES. F. GOTCH AND V. HORSLEY 



7th lumbar posterior root. Effects of 35 and 20 were obtained from excitation of the 

 posterior column on the same side, and an effect of 1 with excitation of the posterior 

 column of the opposite side ; no effect followed the excitation of the laterals. This 

 experiment is very difficult in execution, owing to the depressing effect which the 

 severe character of the operation produces in the cord, both directly and indirectly, 

 through shock to the animal. We have tried the experiment several times without 

 success. As far as they go, the results of the second experiment would seem to 

 indicate that the lateral column effect is not present when only one channel of 

 influence, that of the 7th lumbar posterior root, is present, and this result is in 

 accordance with the observations made upon the posterior root itself. It is not 

 impossible that the results of the first experiments with the sciatic nerve given in 

 Section 3, in which an effect was always obtained from the lateral column of the same 

 side, are due to the fact that the nerve investigated was left in connection with the 

 cord by fibres emerging from at least three posterior roots, beside the 7th lumbar, 

 but as we have not been able to carry the investigation of this point further at 

 present, we would merely emphasize the fact that the anatomical connections with 

 the cord were different in the two cases. 



(3.) Summary of the Facts in (1) and (2). 



If now we sum up the results of all these experiments when the nerve investigated 

 is connected with the cord by afferent tracts only, we find that the average effect 

 evoked by excitation of the posterior column of the same side 



147 + 156 + 108 + 28 _ 439 _ 



4 4 



the posterior column of the opposite side 



_ 4 + 39 + 50 + 10 103 



4 ~T 



the lateral column of the same side 



10 + 20 30 



~T~ = = 15 



the lateral column of the opposite side = 0. 



That is to say, as far as these readings go, of the sum of all the effects obtained, 

 the posterior column of the same side was concerned with 110/151 72 per cent, of 

 the effect in the nerve ; 



The posterior column of the opposite side was concerned with 26/151 = 17 per 

 cent, of such effect ; 



The lateral column of the same side with 15/151 = 10 per cent, of the effect ; 



