450 THE SPINAL CORD. 



nearly absent. It is evident that the sensibility of the posterior columns 

 is largely due to the presence of fibres of the posterior nerve roots, 

 which may be included in the irritation, and many of which traverse the 

 outer portion of the posterior columns horizontally in their passage 

 toward the gray matter. The only discrepancy on this subject is in 

 regard to the question whether the fibres of the nerve roots are the only 

 sources of sensibility for the posterior columns, or whether the longitu- 

 dinal fibres of the columns themselves are also sensitive. According to 

 some authors (Yan Deen, Brown-Sequard, Poincare'), the posterior 

 columns have no sensibility of their own, but only what is due to that 

 of the posterior nerve roots; since if these roots be torn out, irritation 

 of the posterior columns no longer produces any perceptible sensation. 

 In the experiments of Schiff and Vulpian, on the other hand, the poste- 

 rior columns, after being divided by a transverse section, and then 

 separated from the adjacent parts for a distance of several centimetres 

 in front of the point of section, still indicate the existence of sensi- 

 bility when subjected to irritation. Irritation of the posterior columns, 

 like that of sensitive tracts generally, produces also movements in va- 

 rious parts ; but these movements are reflex in character, and are simply 

 the signs of an irritation communicated to the nervous centres. 



Sensibility also exists, according to Yulpian, in that portion of the 

 lateral columns which is contiguous to the outer edge of the posterior 

 columns, and to the line of attachment of the posterior nerve roots. 

 But as the irritation is applied to points farther forward, the signs of 

 sensibility in the lateral columns rapidly diminish, and soon disappear 

 altogether. In all these parts, of both posterior and lateral columns, the 

 sensibility, as found by all observers, is most marked, or even exclu- 

 sively situated, in their superficial portions; and experimenters are also 

 generally agreed that the gray substance of the cord, throughout, is 

 destitute of sensibility to the application of any ordinary artificial 

 stimulus. 



Whatever minor points, therefore, may remain in doubt, the principal 

 fact is unquestioned, namely, that the posterior parts of the spinal cord, 

 consisting of the posterior columns and the adjacent parts of the lateral 

 columns, are sensitive to external irritation, especially at their surface; 

 and accordingly inflammation of the meninges, or other diseased action 

 in this locality, may be accompanied by painful irritation of the spinal 

 cord. The irritation thus produced is still more liable to cause pain, on 

 account of the attachment at the surface of the cord of the posterior 

 nerve roots, which are themselves acutely sensitive. 



The properties shown by the anterior columns on the application of 

 artificial stimulus are, on the whole, quite different from those of the 

 posterior columns. There is some difference in the results obtained in 

 this respect by different experimenters. This difference mainly con- 

 sists in the fact that, according to the large majority (Magendie, Longet. 

 Bernard, Brown-Se'quard, Yulpian, Flint), irritation of the anterior 

 columns produces convulsive movement in the parts below ; while 



