ON THE MAMMALIAN NERVOUS SYSTEM. 



469 



In this case the previous heinisection had rendered excitation of the columns on the 

 side of the lesion quite ineffectual, as far as the generation and propagation of nerve 

 impulses into either nerve were concerned. The excitation of the posterior column on 

 the opposite side to the lesion, however, evoked effects in both nerves. It would, 

 therefore, appear that the crossing through grey matter from the one posterior column 

 to the other, and so to the nerves, was in this case below the level of the hemisection , 

 viz., 12th dorsal vertebra. This experiment apparently is contradictory in its results, 

 as regards the crossing from the opposite posterior column, to. that just given ; but 

 putting aside the presence and absence of immediate shock in the two cases respec- 

 tively, it must be remembered that the lesion in this case was two vertebrae higher 

 up. The localisation to the particular column excited of the generated impulses at 

 the area of stimulation is very clearly brought out by this experiment, as well as the 

 failure of production of any crossed effect from the sound (right) lateral column into 

 the left nerve. 



B. Influence on the Nerve Effect of Section of the Posterior Column at} the Same 



Side as the Nerve Observed. 



The influence of the section of one of the posterior columns will be here considered 

 before that due to section of both, for although its effects are more complicated, the 

 experimental procedure by which the changes were produced involved the section first 

 of one and then of the other column. It will be found that the result is extremely 

 definite as regards the particular column operated upon, as the following experi- 

 ments upon two animals, Cat and Monkey, show. It will be noticed that a con- 

 siderable intensity of stimulus was necessary to produce effects in the Monkey. 



