404 



MESSRS. P. GOTCH AND V. HORSLEY 



region, the section of the posterior roots has withdrawn from active service a pro- 

 portion equivalent to about one-third, and rendered them incapable of conducting 1 

 impulses. 



It is conceivable that the cells in the posterior horn, which, in some animals,* are 

 in relation with the posterior root fibres, may have their functional activity impaired 

 by the section and consequent degenerative changes, and that a small part of the 

 diminution may be due to the withdrawal of impulses possibly generated in them. 

 (See Chapter XI.) 



C. Influence of Section of both Posterior Columns and one Lateral. 



In order to ascertain to what extent ascending impulses started by lumbar excita- 

 tion of the lateral column are interrupted by its section, a similar experiment to that 

 described with descending impulses was carried out. An intervening hemisection on 

 the left side and a further division of the posterior column on the right side were 

 made ; there remained only the lateral of one side, the contiguous grey matter, and 

 the anterior columns to bridge across the interruption (MIESCHER). 



The cord was prepared and excited as in all the previous experiments, two strengths 

 of stimulus being used, both more than "minimal." 



It is evident from this experiment that (I) the excitation of the uninterrupted 

 lateral column of the right side alone produces a marked effect ; (2) that the excita- 

 tion of the posterior columns can evoke effects in spite of the interruption in the lateral ; 



(3) that effects can be obtained from the posterior column of the same side with an 

 intensity of stimulus which is not effectual in the case of that of the opposite side ; 



(4) that even with the strongest intensity of stimulus used, excitation of the inter- 

 rupted left lateral column evokes no result. We may, therefore, infer that afferent 

 tracts in the cord lying in one lateral column are brought into relation with the 

 posterior but not lateral column of the other side. The importance of this result will 

 be realised if it be remembered that .it has been concluded from the result of physiolo- 

 gical experiments ( WOROSCHILOFF, &c.), to be detailed in the next chapter (p. 419), that 

 the majority of sensory fibres entering the cord pass into the lateral column of the 

 opposite side, the remainder continuing in the lateral column of the side on which 



* See FREUD'S paper on the cells in Petromyzon. 



