ON THE MAMMALIAN NERVOUS SYSTEM. 



435 



B. Section of the Posterior Column of tlie same side as the Nerve Excited. 



The marked diminution in the effect obtained by hemisection on the same side as 

 the nerve in the one case, and by section of both posterior columns in the other' 

 would seem to imply that the posterior column on the same side, which is common to 

 both these lesions, is the fundamental structure concerned. We shall see that there 

 is every reason to suppose that it is concerned with 60 per cent, of the total effect, 

 that is, with that proportion of the number of nerve impulses, the remainder being 

 pretty equally divided between the lateral column of the same side and the posterior 

 of the opposite side. It will be seen that the direct evidence of the result of section 

 of one posterior column is somewhat complicated by changes in excitability which 

 appear to affect the remaining columns. 



The results were observed in two Monkeys and five Cats, as shown in the following 

 Tables : 



SECTION of Posterior Column on Same Side as Nerve. 



In these Monkeys section of the posterior column on the same side reduced the 

 cord effect by 69 per cent., a very notable amount. Such a large reduction was not 

 often obtained in the Cat ; and occasionally in this animal comparatively insignificant 

 reductions were seen. In such instances, however, the nerve stimulation was 

 observed to evoke violent reflex movements, and, as will be seen in considering the 

 result of section of the opposite posterior column, the opposite uninjured side of the 

 cord became evidently hyperexcitable. 



3 K 2 



