THE SPIRAL, CORD. 391 



general nervous function, performed by the cord as a whole, is there- 

 fore completely demonstrated, and is not subject to any doubtful inter- 

 pretation. 



But the precise path followed by motor and sensitive impulses in the 

 spinal cord is much less easy of determination than in the nerve roots. 

 The methods of investigation are the same in both instances; and are 

 intended to ascertain, first ; What parts of the spinal cord are sensitive 

 or excitable under the -application of artificial stimulus? and secondly; 

 "What parts are the natural channels of transmission for sensation and 

 motion ? The latter question is the more important in a purely physi- 

 ological point of view ; but the former is also of consequence as a 

 guide in experimental research, and also for the explanation of patho- 

 logical phenomena. 



I. What parts of the Spinal Cord are sensitive or excitable under 

 the influence of artificial stimulus? 



The first portions of the cord which present themselves after opening 

 the spinal canal are the posterior columns. The irritation of these 

 columns by artificial stimulus, according to all observers, produces 

 signs of sensibility. This sensibility is most marked in the immediate 

 neighborhood of the posterior nerve roots ; while at the greatest dis- 

 tance from this point, next the median line, it may be nearly absent. 

 It is evident that the sensibility of the posterior columns is largely 

 due to fibres of the posterior nerve roots, many of which traverse the 

 outer portion of these columns in their pas.sa.ire toward the posterior 

 horns of gray substance. The only discrepancy on this subject is in 

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

 sensibility for the posterior columns, or whether the longitudinal fibres 

 of the columns have also a sensibility of their own. Irritation of the 

 posterior columns, like that of sensitive tracts generally, sometimes pro- 

 duces movements in various parts ; but these movements are reflex in 

 character, and are the signs of an irritation communicated to the ner- 

 vous centres. 



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

 lateral columns contiguous to the posterior nerve roots. But as the 

 irritation is applied to points farther forward, the signs of sensibility 

 rapidly diminish, and soon disappear altogether. In all these parts, of 

 both posterior and lateral columns, the sensibility is most marked, 

 or even exclusively situated, in their superficial portions ; and experi- 

 menters are generally agreed that the gray substance of the cord, 

 throughout, is destitute of sensibility under the application of 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 half of the 

 lateral columns, are sensitive to 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 



